Grantville Gazette 38

Hydrogen: The Gas of Levity

Hydrogen was probably made by Paracelsus in the sixteenth century, and was described by Johann Baptista van Helmont in 1625. It's not only the gas with the greatest intrinsic lifting power (once called "levity"), hence very important for airship development, it's also an extremely important industrial chemical.

Before the twentieth century, the principal uses of hydrogen were in ballooning and in the oxyhydrogen torch. Later, it was used to hydrogenate and reduce other chemicals. Hydrogenation of oils was introduced in 1897-1913, and the Haber-Bosch process for manufacture of ammonia from nitrogen and hydrogen in 1913. Water gas (a hydrogen-carbon monoxide mixture) was used to make methanol in 1922 and hydrocarbons (Fischer-Tropsch process) in 1935.

Hence, there will be many parties interested in finding ways to produce it cheaply, in acceptable purity, on a large scale.

The impurities will vary depending on the nature of the production process, but they typically include carbon monoxide and dioxide, nitrogen, oxygen, water vapor, hydrogen sulfide, carbon disulfide, arsine, phosphine, silane and methane. (Ellis 598). These impurities reduce lift (1% air reduces lift by 1%) and some of them attack the gas cell envelope (Greenwood 234).

Under a pressure of one atmosphere, at a temperature of 20^oC (68^oF), one pound of hydrogen gas will occupy 191.26 cubic feet (so 1000 cubic feet is 5.23 pounds), and one kilogram will occupy 11.94 cubic meters (one cubic meter is 35.2 cubic feet). A 10^oC increase in temperature will cause it to expand by 3.4%, and the corresponding temperature drop will contract it by the same percentage.

It's interesting to survey which methods of manufacturing hydrogen are mentioned in known or likely Grantville literature:

McGHEST: McGraw-Hill Encyclopedia of Science and Technology

CCD: Condensed Chemical Dictionary

MI: Merck Index

C amp;W: Cotton amp; Wilkinson, Advanced Inorganic Chemistry

EB11: Encyclopedia Britannica, 11th edition (19110

EBCD: Britannica 2002 Standard Edition CDROM, based on the Encyclopedia Britannica, 15th ed. (1998).

The provided information is minimal; details will need to be worked out. And Grantville literature definitely doesn't even list all of the methods that have been used since the nineteenth century; it's possible that some of the overlooked ones will be rediscovered.

Offord, "A Trans-Atlantic Airship, Hurrah" (Grantville Gazette 36) discussed three of these methods: "electrolysis of water, the action of acid on metal, and . . . forcing steam over red hot iron." He rejected electrolysis as requiring too much energy and acid-metal as not producing hydrogen as fast as steam-iron.

In canon, Kevin and Karen Evans, "No Ship for Tranquebar, Part Three" (Grantville Gazette 29) says that the Royal Anne carries a portable hydrogen production system that can be used in Tranquebar to refill the gas cells. This system involves "spraying water on red-hot iron," i.e. flash steam. The Grantville balloonist, Marlon Pridmore, mistakenly believes that this apparatus was used in the American Civil War. While John Wise attempted to use it in 1861, it "proved to be too cumbersome and expensive for practical use." (Haydon 7). Instead, the Union adopted the acid-iron reaction. (Tunis, Crouch). However, steam-iron apparatus was used briefly during the 1790s, and it proved to be a suitable technology for large-scale, stationary hydrogen plants.

While the steam-iron reaction is certainly a plausible basis for a hydrogen generator, I believe that it would be productive to consider the alternatives. I break these down into those for field use and those for large-scale production; note that the steam-iron process is considered in the second category, consistent with early-twentieth century practice.

Pay attention to the gas production rates; airships are big and it takes a long time to fill them. If an airship is 1,000,000 cubic feet (half the size of the Royal Anne in A Ship for Tranquebar), then at 1,000 cubic feet/hour, it would take 1,000 hours of nonstop operation. Just to complicate matters, that assumes no losses; Wilcox says that production must be at least 50% in excess of the airship capacity.

Field Production of Hydrogen

In the first attempt to deploy a balloon during the American Civil War, James Allen had his balloon inflated with city gas in Washington and then transported the inflated balloon by wagon. However, this was really not practical. One of Allen's balloons was, while wagon-tethered, blown by a gust of wind into a telegraph pole, and later John Wise had an inflated balloon caught by roadside trees. (Fanton).

The airships of the 1632 universe are likely to be far larger than these nineteenth century military balloons, and thus even less amenable to being transported by road in inflated form. Hence, the hydrogen must be either made at, or brought to, their launch site.

All of the methods described in this section have been used in the field. They are portable (they produce a considerable amount of hydrogen relative to the weight of the reactants other than water), but expensive to operate. In the late-nineteenth and early-twentieth century, armies used them only for operations remote from railroad support, as otherwise it was easier to use compressed hydrogen shipped from stationary plants. (AGLJ).

The following table compares them from a reactant portability standpoint:

(1) Greenwood 234 @20^oC; (2) Teel (various) (@40^oF.

The underlying logic of the above table is that water is probably available locally and hence needn't be transported. The table unfortunately doesn't include the weight of the apparatus itself. The apparatus would be conveyed by wagon, truck, rail car or ship. It also doesn't include the weight of fuel if heat must be supplied, e.g., to make steam.

Note that hydrogen produces about 72 pounds/1000 cubic feet of lift, so carrying the reactants around so you can make more hydrogen at your destination, to refill the airship, is a losing proposition unless you are using hydrolith or Maricheau-Beaupre processes.

Steam-iron is not on Greenwood's list of portable processes, despite its use in the Napoleonic Wars (see below), but by my calculations, you would need 97 pounds of iron. Of course, if there's no fuel available locally, that will have to be brought, too.

Acid (vitriol; wet) process. This was the first process used to manufacture hydrogen for ballooning. In essence, a hydrogen-containing acid is reacted with a metal. Usually, the acid is sulfuric acid and the metal is iron. The reaction was described by Turquet de Mayerne in 1650, but it may well have been known pre-RoF-supposedly Paracelsus knew of it (Rand 34).

Formally speaking, the reaction (with stoichiometric quantities indicated in parentheses) is:

H₂SO₄ (98 grams) + Fe (56 grams) -› H₂ (2 grams) + FeSO₄ (152 grams).

(Note that if you keep the ratios the same, you may change the units to kilograms or pounds or tons.)

Unfortunately, the method only produces 2 grams of hydrogen for every 154 grams of reactants. And please note that the above assumes pure reactants, and in even the mid-eighteenth century, the sulfuric acid was only 35-40% pure. (Wikipedia/Sulfuric Acid). It can only be purified by simple distillation to 78%.

The metal-acid reaction is also cumbersome and dangerous for military-expedient field production, because of the acid that must be carted around. On April 11, 1862, the single line tethering General Porter's balloon broke, having been damaged by an acid spill, resulting in an unplanned free ballooning experience (Crouch 375). In 1830, on the brig Vittoria, the balloonist's "carboys of sulfuric acid were accidentally broken by the rolling of the ship, and caused a fire that resulted in damage amounting to some 80,000 francs." (Haydon 17). During the Spanish-American War, it was reported that if the acid were kept in glass carboys, the stoppers were often knocked out or the necks of the carboys broken during transport over rough roads. Lead-lined iron cylinders proved more convenient, but then the lining had to be perfect, to avoid acid leakage. (Maxfield).

The transport safety issue could be addressed by producing the sulfuric acid at the launch site by the seventeenth-century Glauber process. That is, you use saltpeter and steam to convert sulfur to sulfuric acid. This can be done in glass or lead-lined chambers. Of course, you then have to cart sulfur, saltpeter, the reaction chamber, and fuel for the boiler.

Alternatively, you can use the original Philips 1831 version of the contact process. This needs just sulfur, a platinum catalyst, and heat, not saltpeter, so it's more portable. For availability of platinum, see my prior chemical and mineralogical articles. Note that platinum catalysis is poisoned by arsenic impurities in the sulfur.

There are other problems with hydrogen production from the metal-sulfuric acid reaction. Iron is likely to contain sulfur, which reacts to form hydrogen sulfide. Depending on the carbon, phosphorus, sulfur, arsenic and silicon content, it may form significant amounts of methane, phosphine, hydrogen sulfide, arsine and silane. (Teed 41, Molinari 133).

Zinc (an iron substitute) is perhaps less liable to contribute significant impurities, but it and sulfuric acid may both contain arsenic, which will form arsine. (Englehardt 124; Greenwood 230; Teed 42). All of the cited impurities necessitate purification treatments; note that acids will attack the envelope. At a minimum, you will want to pass the gas through water.

While more zinc than iron is required (the weight ratio of metal to acid must be 0.66:1 rather than 0.57:1), and in the seventeenth century zinc would be the more expensive metal. In the early-twentieth century the byproduct zinc sulfate was of greater commercial value than iron sulfate. (Teel 42). Iron sulfate may be used in manufacturing other iron compounds and iron gall ink, as a mordant, and as a developer in the collodion process. Zinc sulfate may be used to remedy zinc deficiency in soil, to coagulate viscose rayon into fibers, in the manufacture of lithopone, in zinc plating, and as a mordant, preservative, and corrosion inhibitor.

Also, zinc is higher on the reactivity series, and hence hydrogen production is likely to be faster. (And still more reactive metals, such as aluminum, will react even with water, and the acid can be dispensed with-see below.)

Still, the iron-acid reaction appears to have been respectably rapid in practice. On April 5, 1862, Lowe arrived at the lines shortly after noon and ascended at 5:20 (Crouch 375). So, in five hours, he inflated a balloon, and the smallest of his balloons was 15,000 cubic feet. (358).

As the reaction progresses, the metal is covered with the sulfate, protecting it from further reaction. In the nineteenth century, mechanical and hydraulic devices were devised to scrape or wash off this coating. (Molinari 133).

The vitriol process was first used for ballooning by Jacques Charles in 1783; he reacted 1100 pounds of iron filings with 550 pounds of acid. It took three days and nights to produce enough hydrogen to fill a balloon with a capacity of less than 1400 cubic feet. (Sander). Note that Charles used too much iron and not enough acid, a mistake that someone with modern high school chemistry wouldn't make. It's possible that he had problems exposing all of the iron to the acid.

In 1785, Aime Argand produced hydrogen for the Blanchard-Jeffries crossing of the English Channel. Jeffries paid 100 guineas for materials, most of which was "spent on the most expensive item, the acid." Argand's work area was about 100 feet in diameter. He placed fifty pounds of "parings of iron plates" and one hundred pounds of "cast iron trimmings" in the bottom of each of twenty-six 54-gallon half-barrels, and added hundred pounds of sulfuric acid to each vessel. That implies use of 3,900 pounds of iron and 2,600 pounds of sulfuric acid to produce. the required 9,000 cubic feet of hydrogen. The half-barrels were capped with an upended tub with a central pipe; hydrogen rose through this pipe into a leather hose, which conveyed it to a larger barrel for "purification and cooling before transfer to the balloon." Occasionally, the half-barrel was opened and the iron stirred around with an iron rod, to expose fresh surface. (Crouch 81).

The acid process was also used by Union balloonists during the American Civil War. Thaddeus Lowe designed the army's portable gas generators. The generator was a strongly braced wooden box 11 feet long, 5 feet high, and 3 feet wide, which meant that it was able to fit in a standard wagon body. There was a manhole on top and a rear door. It was acid-proofed inside, with shelves to hold 3,300 pounds of iron filings, submerged in three feet of water. Sulfuric acid was introduced through a rooftop copper funnel, and the produced gas rose through a six-inch hose. This hose was connected to the cooler box, which was five feet long and has a smaller box inverted inside. The cooler box was partially filled with water; the gas entered the cooler box underwater and bubbled up, around cooling baffles, eventually escaping into a second hose. This conducted the gas to the purifier box, which was similarly constructed, but contained a limewater solution. (That would absorb carbon dioxide.) A third, twelve-inch hose ran from the purifier box to the balloon. (Crouch, 358; Tunis 88-89).

A British observer reported in 1862 that the iron was inexpensive since "any old iron" would do, and that the sulfuric acid "in large quantities is cheap, and with proper precautions, very easy to carry." (Templer 174).

The acid-iron process was used to fill the giant (118 feet diameter, 882,900 cubic feet) captive balloon erected by Giffard for the 1878 Paris Exhibition; 190 tons acid and 80 tons iron were consumed. (Baden-Powell 741).

In 1883, if 250 pounds of iron were used to make 1,000 cubic feet of gas, the cost of production was 1? 5s per 1,000 cubic feet. A good portable apparatus filled a 6,000 cubic foot balloon in four hours. (Powell).

In the Andree North Pole expedition of 1893, zinc was used; the costs in kroner were estimated to be 1950 for the apparatus (producing 5300 cubic feet/hour), 3,000 for the raw materials (zinc and sulfuric acid, in 20% excess), and 1600 for the technical expert's salary. However, the expert decided to use wrought iron instead of zinc. (Capelloti 149). Nonetheless, the 1896 British manual of military ballooning favored zinc. (Taylor 169). In the 1632 universe, zinc is a rather rare commodity, and so our aeronauts will almost certainly use iron.

The acid process was again used by the 1907 Wellman expedition. My source mentions a number of interesting points, including that perfume is added to the hydrogen stream (by passage through sponges filled with muronine) so leaks are readily detectable, and the gas is piped through coke (to dry it), caustic soda (to remove residual acid), potassium permanganate (to remove arsine, stibine and phosphine?) and calcium of lime (to remove carbon dioxide?). (Capelloti 152ff).

Nonetheless, even in the early-twentieth century, the acid process was considered too expensive for large-scale industrial production, unless the hydrogen was simply a byproduct of producing a salable metallic salt. (Ellis 515). For example, in 1904, figuring zinc at 9.75 cents/kg and sulfuric acid at 1.75, 1 kg zinc and 2 kg acid would theoretically produce 32 grams (about 360 liters) hydrogen for 12.25 cents. Taking into account that the metal-acid reaction is usually incomplete, the electrolytic method (see Large Scale Production below) could produce the same volume with 800 ampere-hours (2 kwh @ 2.5V), with a then cost of power of 0.5 cents (hydroelectric) or 2.5 cents (coal/steam)(Englehardt 125). Ellis (518) adds that "the operating cost of an electrolytic plant [in 1917] is one-fifth that of a zinc-acid plant and there are no acid-eaten hydrogen pipes or freeze-ups in winter."

Base-metal process. This is alluded to by EB11/Hydrogen, which recommends reacting sodium or potassium hydroxide with zinc or aluminum, or zinc with an ammonium salt other than nitrate. The zinc-sodium hydroxide reaction produces hydrogen of high purity, but it has arsine (from the zinc) and caustic soda impurities.

Teel (44) says that the reaction of zinc with magnesium hydroxide has been used for ballooning.

In the Russo-Japanese War, the Russians reacted 30% caustic soda with aluminum scrap. They transported twenty-four generators and six coolers (the reaction generated a lot of heat) with the aid of fifteen horses, and this setup was sufficient to fill a 400 cubic meter balloon in thirty minutes. (Molinari 134).

Base-Carbon. A base like caustic soda may be reacted with coal to produce hydrogen:

4NaOH + C -› Na₂CO₃ + Na₂O + 2H₂.

The coal may generate methane, arsine or hydrogen sulfide impurities. (Teel 60).

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Alkali (Alkaline) Metal-Water. The most common reaction is

2Na (46 g) +H₂O (18 g)-›2NaOH (62 g) +H₂ (2g).

The reaction of water with sodium is much more vigorous than that with iron; the water need not be provided in the form of steam. In fact, the reaction had to be slowed down, for example, by supplying the water as a fine spray, or incorporating the sodium into a briquette with an inert binder. (Taylor 127).

Since water would be available in the field, only the sodium, a light metal, had to be transported. The catch was that metallic sodium was expensive-5s/pound in 1883, so 1,000 cubic feet of hydrogen would cost 22?. (Powell). Also, sodium was dangerous to transport, because of its reactivity with water.

Other alkali metals, such as lithium, could be used in placed of sodium; 22.5 pounds of lithium hydride, reacted with equivalent water, would produce 1,000 cubic feet hydrogen. (Roth 30). They are, if anything, more expensive than sodium so these are strictly laboratory methods.

The same is true of the alkaline earth metals, of which magnesium will probably be the cheapest.

Aluminum amalgam-water. If a small amount of mercury (or mercuric salt) is added to aluminum powder, to make an amalgam, the latter will react with water to form aluminum oxide, hydrogen, and pure mercury. The latter may be reused to make more amalgam. One pound of aluminum yielded 20.5 cubic feet hydrogen. (Taylor 129).

This procedure was practical in the early-twentieth century, thanks to the Hall-Heroult electrolytic process for making aluminum.

The Mauricheau Beaupre "activated aluminum" variant involves adding water to a mixture of fine aluminum filings, mercuric chloride, and mercuric cyanide. One kilogram solid mixture, so reacted, yields 1.3 cubic meters in about two hours. The apparatus required is minimal. (Ellis 525). The aluminum must not contain copper (Teel 70).

Hydrolith Process. This was another field expedient, exploiting the reaction

CaH₂ (42 grams) +2H₂O (36 g) -› Ca(OH)2 (56 g) +2H₂ (4 g).

So only 55 pounds of calcium hydride is needed to obtain 1,000 cubic feet hydrogen. The calcium hydride would be made at base, from a calcium salt (oxide, chloride) and hydrogen in presence of a reducing agent (sodium, magnesium).

The French used this system in the early-twentieth century; the calcium hydride was carried on latticed trays, immersed in water; the hydrogen rose up. This gas was contaminated with water vapor, which was removed by passing it over dry calcium hydride. (Taylor 128). You also need to remove ammonia, and heat evolution can be a problem. A typical six generator wagon produces 15,000 cubic feet/hour. (Greenwood 229).

A related, speculative process uses lithium hydride:

LiH₂ (9 grams) +4H₂O (72g) -› 4 LiOH (75g)+ 3H₂ (6g).

Note the enormous yield of hydrogen relative to the amount of lithium hydride. This would be great for the field. The ratio is good enough so it's feasible (from a weight, not necessarily a safety standpoint) to bring the lithium hydride on board for use at a destination to make more hydrogen. It has even been suggested that the reaction could be used to produce hydrogen while in flight, reacting the hydride with water ballast (warning: this can be a violent reaction!), and then dropping the lithium hydroxide. (Teel 67). But the cost of lithium hydride, which is made by reacting lithium metal with hydrogen; is prohibitive (even 1992 price was $72/kg-Kirk-Othmer).

Silicol Process. The basic reaction was

2NaOH+Si+H₂O-›NaSiO₂+2H₂.

It was first proposed in 1909, and became a popular military field expedient, especially on ships. Not only were the ingredients quite safe to transport, the produced hydrogen was of "very high purity." (Taylor 143).

Initially, commercially pure silicon was used, but this was replaced by the cheaper ferrosilicon, which was used for deoxidizing steel and introducing silicon into alloys. Ferrosilicon may be made by reducing sand (silica) with coke in the presence of iron. The ferrosilicon typically contains small amounts of phosphine, arsine, and hydrogen sulfide. (Greenwood 227), as well as air. (Teel 45). The silicon content has to be over 80% for reasonable effectiveness, and particle size affects the production rate. (Teel 50). The caustic soda must be neither too dilute nor too strong. (Teel 52).

In addition, there is an explosion hazard. The ferrosilicon dissolves only slowly in cold solution, and thus can accumulate. But the reaction produces heat, and as the solution gets hotter, the accumulated ferrosilicon is attacked, leading to rapid evolution of hydrogen. (Teel 57).

A transportable plant can produce 60-120 cubic meters/hour, whereas stationary plants of up to 300 capacity have been constructed. (Ellis 523) [The typical portable plant was mounted on a three ton truck and produced 2,500 cubic feet/hour; the largest portable apparatus produced 14,000 cubic feet/hour. The reaction has also been used for stationary production at up to 50,000 cubic feet/hour. (Greenwood 226).

For the 1929 British R100 airship, "249 tons of caustic soda and 183 tons of ferro-silicon produced 8,610,705 cu.ft of hydrogen (20.3 tons) and 929 tons of sludge [sodium silicate]." (Wilcox). The R100 had a gas capacity of about 5,000,000 cubic feet, so the gas produced was substantially in excess of the capacity. Wilcox's information about production rate is somewhat contradictory. He says that the plant could produce 60,000 cubic feet/hour, but that the highest daily production was 500,000 cubic feet. Also, that it took ten days to fill fourteen of the R100's fifteen gas bags.

An alternative reaction that can use the same apparatus exploits the reaction of aluminum with sodium hydroxide, and was used by the Russians in the Russo-Japanese War. (Taylor 145-6). It can produce 10 cubic meters/hour. (Ellis 523).

Hydrogenite process. This starts with a compressed block of a mixture ("hydrogenite") of silicon, caustic soda, and soda lime, kept in an air-tight container. To use, the container is placed in a water jacket, a match or a red hot wire is applied to a small hole in the lid. The silicon is oxidized to silica, a heat-releasing action. This heat makes possible the reaction

Si+Ca(OH)₂+2NaOH-›Na₂SiO₃+CaO+2H₂.

The heat turns the water to steam and eventually this is permitted to enter the generator, increasing yield by a reaction of the silicol type.

While it requires that 50% more material be provided than for the silicol process, much less water is needed, which would be advantage for desert use. (Taylor 168). A production rate of 150 cubic meters/hour is possible(Ellis 521ff). The portable wagon-based apparatus of the French army, featuring six generators grouped around a central washer, produced 5000 cubic feet/hour. (Greenwood 228).

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Another "dry" method (by Majert and Richter) involves heating a mixture of zinc dust and slaked lime to redness, but the Prussian army deemed it too slow (it took 2-3 hours to fill a balloon). (AGLJ).

Large-Scale Production

Some processes are best suited to production of hydrogen on a large scale and at a low cost. Unless the airship hangar happens to be near the manufacturing plant, the gas will have to be compressed and shipped in containers (which must be returned empty), which increases the cost.

Steam-Carbon. First, water gas (a mixture of carbon monoxide and hydrogen) is produced by reacting red-hot coke or coal with steam at 800 or 1000^oC (2002McGHEST):

H₂O (18 grams) + C (12 grams) -› H₂ (2 grams) + CO (28 grams).

Just making steam, by itself, consumes fuel. According to EB11/Railways, the faster you burn coal, the lower the efficiency. With Indiana block coal (13000 BTU/lb):

Those are for a 1900 locomotive boiler. and a stationary plant might have a higher efficiency. Additional coal would need to be burnt to superheat the steam to the required temperature. The increase in coal consumption to achieve 100^oC superheat is 5.5%, for 150, 8.3%, and for 200, 11%. (Stovel 1475). (Superheated steam is more efficient than ordinary steam, however, in terms of the heat content of the steam relative to that of the coal burnt to produce it. (Babcock 137ff).

With the Baldwin experimental locomotive 60,000 (1926), designed for high efficiency, evaporation declined from 10 to 6.5 pounds water per pound of dry coal, as firing rate increased from 30 to 150 lb/ft² grate/hr. and superheat increased from 180^oF to 257^oF. (Pennsylvania RR, Fig. 19).

If you burn carbon in air, the hydrogen will be contaminated with nitrogen from the air. This can be avoided by burning pure oxygen into carbon monoxide, but then you must provide the oxygen somehow.

The process can be operated on a mostly continuous basis; occasionally clinker must be removed. (Teel 81). Water gas has impurities, such as hydrogen sulfide and ash (84).

Water gas in turn can undergo this shift reaction, discovered by Felice Fontana in 1780:

CO (28 grams) + H₂O (18 grams) -› CO₂ (44 grams) + H₂ (2 grams)

Since exposure to CO (carbon monoxide) is dangerous, naturally there was interest in conducting the steam-carbon reaction in such a manner as to minimize its formation, i.e., to obtain the mixture of carbon dioxide and hydrogen:

2H₂O + C -› CO₂ + 2H₂.

Gillard found that this could be accomplished by use of an excess of steam. The carbon dioxide can be removed on a batch basis (see below), but unfortunately it proved "very difficult to carry this out in practice on a large scale. . . ." (Sander).

BAMAG worked at a low temperature (at which the reaction equilibrium is favorable), but with catalysts (typically nickel) to speed up the reaction. This results in what is reportedly the cheapest method of producing hydrogen (1 shilling/9 pence per 1000 cubic feet), but unfortunately the product contained 4% nitrogen, a serious disadvantage for aeronautical use. (Greenwood 162). 2002McGHEST suggests a reaction at 350^oC over an iron oxide catalyst.

Griesheim-Elektron instead disturbed the water gas equilibrium by "absorbing" the carbon dioxide with lime or other alkali. Cost of production (1912) was 2s/2s.5p-2s/9p per 1000 cubic feet for a moderate size plant. While the process can be carried out at a lower temperature than the steam-iron process below, reducing maintenance costs, "the handling of the large amounts of lime presents some difficulty." (Greenwood 167ff).

Of course, we can eschew the shift reaction, and remove the carbon monoxide with an "absorbing agent" or by liquefaction. EB11/Carbon notes that it is "rapidly absorbed by an ammoniacal or acid (hydrochloric acid) solution of cuprous chloride," but the resulting hydrogen is only 80% pure. (Sander) Later, Frank and Caro thought of employing heated calcium carbide. This conveniently "absorbed" not only carbon monoxide, but also carbon dioxide and nitrogen, and in the process produces graphite and calcium cyanamide. (Sander; Elis 597).

Liquefaction (Linde-Frank-Caro method) at -200^oC works well, but small-scale plant costs are high (Ellis 460) and concerns have been expressed about the dangers of working with compressed carbon monoxide (595). In 1912, a plant producing 3500 cubic feet hydrogen/hour cost about 13,000 pounds, and had a cost of hydrogen production of 3 to 4 shillings per 1000 cubic feet. (Greenwood 174).

A little more explanation of liquefaction may come in handy. A gas can only be liquefied if cooled below its critical temperature; at that temperature, it must be compressed to the critical pressure; at lower temperatures, lesser pressures are needed for condensation.

(Teel 114ff).

It can be seen that cooling water gas to -200^oC (usually by surrounding it with liquid nitrogen boiling under reduced pressure) permits separation at normal pressure. Or one may use a more moderate cooling and greater-than-atmospheric pressure. The liquefied carbon monoxide is used to pre-chill the incoming water gas, and then is burnt as a fuel. (Teel 119).

Steam-iron (dry) process. Lavoisier was the first to show (1783) that hydrogen could be produced in an acid-free reaction, by reacting iron with steam. And Argand recognized that the yield would be higher than with the acid process. (Clow 159).

There are really two different steam-iron processes, the single step non-regenerative one for field use, in which iron is consumed, and the two-step cyclic one, in which iron oxide is reduced with water gas to iron, and then the iron is reoxidized to iron oxide with steam, for large plants. The former has the simplified equation

Fe ( 56 grams) + H₂O (18) -› H₂ (2) + FeO (72)

Steam-iron generators were used by the world's first air force, the 1794 Compagnie d'Aerostiers, as this process was safer, cheaper, and most important, because the sulfuric acid was needed for gunpowder manufacture. (Boyne 378; Langins 536).

In autumn 1793 Coutelle placed iron scrap into a three foot long, one foot diameter cast iron reactor pipe, which in turn was placed inside a furnace. Water was introduced into the pipe, and turned to steam (Langins 537). There's gas flow rate data for six experiments: 0.32-1.114 (0.544 average) m³/hr. Water flow rates were in the 22-58 g/min range. (539). In one experiment, in the course of four days and three nights, 23.83 cubic meters hydrogen was produced. (538). That corresponds to about 40% yield.

The scale of these experiments was almost 150 times that of in the 1780s, and a scale-up problem was encountered: carbon dioxide. The wrought iron musket barrel used in the laboratory experiments was essentially free of carbon, but Coutelle's cast iron pipes were up to 4.5% carbon. The carbon dioxide would reduce the buoyancy of the gas; the density of the produced gas ranged from one-half to one-sixth that of air; pure hydrogen would be about one-fourteenth. The problem was addressed by bubbling the gas through lime water, but even then the gas was on the heavy side (possible explanations include failure to change the limewater frequently enough; use of too high a gas flow rate; or failure to first remove dissolved air. (549).

In March 1794, the technology was taken to a new level; each of seven reactor pipes, eight feet long, one foot in diameter, and one inch thick, were stuffed with 540 pounds iron. (This was essentially the system taken into the "field," see Hoffmann 24). Note that each pipe, so loaded, weighed a ton. At this new scale, a problem that had been minor before became more significant: if the reactor pipes were heated too vigorously; they cracked or melted (cast iron melts at 1050 ^oC). (543). Sometimes the heating was uneven, with some pipes softening and others not heated enough (546). It didn't help that the pyrometers in use were poorly calibrated, and the pipes were poor in quality; locally produced pipes were even permeable to water! (547). There were also problems with the cement used to seal the reactor pipe to the exterior tubing; it cracked and thus gas was lost. (546, 550).

These French steam-iron generators are best viewed as "relocatable" rather than truly portable field equipment. After the 1793 experiments, it was envisioned that a balloon could be filled five or six days after the arrival of the generator equipment at the launch site. (Langins 542). In actual practice, the furnace, with a twenty-foot tall chimney, took twelve days to build (16,000 bricks were needed, and local bricks weren't necessarily refractory enough). (546). In contrast, the American Civil War generators were up and running within a matter of minutes.

With these main generators, it reportedly took 50 hours to fill a 30 foot diameter (4500 cubic feet) balloon (Delacombe 31) and such production was considered slower than the acid-iron method. (Boyne 378).

However, the French did also have a smaller scale furnace that had a single pipe and could be assembled in an hour. It used as much fuel as the large furnace, but could produce 800 cubic feet in 48 hours using 180 pounds of iron. It was used to "top off" an inflated balloon that had leaked while transported from the main facility to the launch site. (Langins 552).

The French military ballooning company was abolished in 1799, and the steam-iron process didn't return to public notice until 1861. Then, John Wise proposed that the Union adopt a horse-drawn generator wagon with two eighteen-inch cylindrical retorts made from boiler plate, a boiler, and a firebox, the latter generating heat for both steam generation and for heating the solid reactants (a combination of charcoal and iron turnings, so this was really a blend of the steam-carbon and steam-iron methods) in the retorts. (I visualize this as a bit like a locomotive, but with retorts replacing the piston cylinders.) A tender was to carry water, iron turnings, and firewood, again much like a locomotive. He asserted that a 20,000 cubic foot balloon could be inflated in four hours.

Contemporary calculations showed that for a single inflation, the wagon would need to carry 7500 pounds of iron turnings, and twenty-two cubic feet of water (1364 pounds by my calculation). The machinists declared that the generator would weigh more than five tons, and of course the tender would be additional. The estimated cost of the generator was $7,000. The government declined to fund the project. (Haydon 77).

The British experimented with the steam-iron method in 1879. Captain Templer reportedly generated hydrogen at a rate of 1,000 cubic feet/hour (BLE 109). The apparatus weighed 3.5 tons, was carried in three general service wagons, and could generate enough gas for two balloons in twenty-four hours. "But the apparatus did not prove satisfactory." (Baden-Powell 742). Possibly, the British expectations were too high; Templer said that he wanted a production rate of 5,000 cubic feet/hour. By 1885 the British had switched to shipment of compressed hydrogen to the field. (Moedebeck 226).

Insofar as field use in the 1632 universe is concerned, we clearly aren't going to want to go with an installation like that used in the French Revolution. The question is whether a viable system could use a firebox and boiler similar in size and design to that of a nineteenth-century steam locomotive, and then route the steam through reactor tubes to oxidize the iron. (Coutelle in fact considered use of steam engine cylinders as reactor tubes-the steam engine existed in 1794, even though the steam locomotive didn't.) Such a system could at least be transported by rail.

From the equation quoted earlier, it takes nine pounds of water to make one pound of hydrogen, and 5.23 pounds hydrogen occupies 1000 cubic feet (20^oC). A pound of coal should evaporate five to ten pounds water (although more coal would be needed to heat the iron and to superheat the steam to the most effective reaction temperature). But it seems to me that the steam-iron process on the locomotive scale should work (although not necessarily better than the acid-iron process).

One thousand cubic feet hydrogen provides about seventy-two pounds of lift. And to produce it, you need one hundred ten pounds of iron. So carrying iron on board an airship for hydrogen production at destination is a losing proposition.

The purity achievable with the early-twentieth century embodiment of the steam-iron process is 98.5-99% (Taylor 172) . The forward reactions are:

2H₂O + 2Fe -› 2FeO + 2H₂

3H₂O + 2Fe -› Fe₂O₃ + 3H₂

4H₂O (72 grams) + 3Fe (168) -› Fe₃O₄ (232) + 4H₂ (8)

The reaction products of the simple process do have possible utility; FeO as a black pigment, Fe₂O₃ as a red pigment and as jeweler's rouge, Fe₃O₄ as a black pigment and a catalyst in the water gas shift and other reactions. And, of course, all can be smelted to regenerate iron. Which, of course, is one stage of the regenerative process.

Getting the regenerative steam-iron process working properly isn't trivial. The iron-producing reduction with water gas is endothermic and the hydrogen-producing oxidation is exothermic.

It may be possible in a large plant to use waste heat from retorts that are in the steaming step stage to warm retorts that are in the water gas stage. However, that heat isn't enough, by itself. (Taylor 55). Both the carbon monoxide and the hydrogen of water gas are reducing agents, but there are fuel economies in working at lower temperatures, which favor carbon monoxide activity. The catch is that this results in higher levels of carbon and carbon monoxide in the next step. (Greenwood 178)

Temperature has several different effects. Higher temperatures shift the equilibrium point in favor of the reverse reaction, but the reaction is forced forward by continuously removing hydrogen and supplying fresh steam (Greenwood 275). The permeability of the iron to steam and hydrogen is reduced by fritting above 900^oC. However, the reaction is very slow below 650^oC. (Teel 88).

In the Lane multi-retort system, dry steam is used at a pressure of 60-80 psi without any superheat; the exothermicity of the reaction raises the reaction temperature adequately. In a single retort system, the same pressure is used with partial superheat. (Taylor 51).

Ideally, the "contact mass" of iron is porous (to maximize reactive surface area) yet robust (so it doesn't crumble into dust and create a back-pressure). Also, it is resistant to local overheating, which results in sintering. The choice of iron (spathic ore is best) makes a difference; "before 1917, American producers . . . imported their contact material, mainly from England." (29). Spongy iron-manganese ores will prove to work better than ordinary iron ore. (Ellis 495, 502). It may be possible to catalyze the reaction with copper, lead, vanadium or aluminum. (Ellis 502).

As iron oxide is formed, it shields the remaining iron from the steam. (Teel 87). Hence, for large-scale economical operation, the iron (which was oxidized to iron oxide) is regenerated. (Ellis 485). That means that you may start with iron ore (Fe₂O₃) instead of iron. About six tons iron ore are needed to produce 3500 cubic feet/hour. (Teel 88). The iron oxide is reduced (probably with water gas), and then you introduce the steam to react with the iron and produce the hydrogen. Then you repeat the cycle. Typically, consumption of water gas is 2.5 cubic feet per cubic feet hydrogen in a multi-retort plant and 3.5 in a single retort one. (Teed 97).

The water gas, in turn, is produced by the steam-coal process discussed earlier. Soft coke consumption is at a rate of about one ton for every 6500-7000 cubic feet hydrogen. (98).

However, the water gas must be purified or the impurities will result in formation of adverse deposits on the contact material or gaseous contaminants (hydrogen sulfide, carbon dioxide, etc.) in the hydrogen. (Ellis 487ff; Roth 25). There is also sulfur in the iron ore (Teel 93), and sulfur compounds are especially problematic. (Greenwood 181). Measures taken to cope with these problems increase the volume of water gas required and also reduce the production rate. (Ellis 487). Even then, the iron eventually loses its activity. (Ellis 499). "An unsuccessful attempt at commercial production . . . was made by Giffard in 1878. The iron rapidly became inactive due to sintering of the material and to chemical reaction with impurities in the reducing gases used." (Taylor 27).

Even in modern embodiments, the initial product contains a large fraction (61%) of steam; that can be condensed out. There will also be carbon monoxide (from the water gas) and nitrogen (presumably from dissolved air in the water used to make the steam). (Brewer 232). These are purified out.

The most common factory implementation of the regenerative steam-iron process is the Lane process; it's relatively economical of fuel but there's more deposition of carbon and (thanks to side-reaction with steam) higher carbon monoxide content. A plant producing 3500 cubic feet/hour might have 36 vertical retorts, each 9 inches diameter and 10 feet high. (Greenwood 178). Despite the recommendations of 2002McGHEST, the typical retort temperature was 650^oC, prolonging the useful life of the retorts. They last 12-18 months, and the ore is good for 6. Water gas is consumed at rate of 2-3 volumes per volume hydrogen, and the cost of hydrogen is 3/- to 4/- per 1000 cubic feet, excluding overhead. (182).

High Pressure Water ("Bergius"). The temperatures are lower (200-300^oC) but high pressure is used (150 atmospheres) to keep the water liquid as it reacts with iron (Ellis 513) or carbon (Ellis 527ff). Common salt, iron chloride or hydrochloric acid accelerate the former and thallium salts catalyze the latter. Bergius built a prototype that produced high (99.95%) purity hydrogen. Since the hydrogen is already pressurized it can be put into bottles without the need for a separate compressor. (Teel 64). While initial cost and floor space requirements were expected to be low (Greenwood 188ff)-a 10 gallon capacity generator supposedly can produce 1000 cubic feet/hour (Teel 65)-I don't think these reactions were ever practiced commercially. Bergius (1913) claimed that hydrogen could be produced for just 2 cents/cubic meter (Greenwood says 1s/4.5p to 1s/11p per 1000 cubic feet.)

Electrolysis of Water. Water was first electrolyzed into hydrogen and oxygen in 1800. (Cleveland 128). Hydrogen is produced at the cathode and oxygen at the anode:

Cathode (reduction): 2 H₂O + 2e^- -› H₂ + 2OH^-

Anode (oxidation): 2 H₂O -›O₂ + 4 H+ + 4e^-

The net reaction is

2H₂O (36 grams) + electricity -› 2H₂ (4 grams) + O₂ (32 grams) .

The reaction requires an electrolyte, so either base (such as potassium or sodium hydroxide) or acid (such as sulfuric acid) is added to the water.

We will want an electrode material that is resistant to attack by the electrolyte, and minimizes the internal resistance. (Ellis 536; Greenwood 195). Acid electrolytes caused continuing corrosion problems and hence alkaline electrolytes became the norm. (Taylor 106). Taylor (105) recommends the combination of a nickel-plated anode and an iron cathode to minimize overvoltage.

The level of oxygen in the hydrogen compartments shouldn't exceed 5.3%, and of hydrogen in the oxygen ones, 5.5%. (Greenwood 202). It's critically important that the cell be designed to prevent the mixing of the hydrogen produced at the cathode with the oxygen produced at the anode, which can result in an explosion. This is usually done with a diaphragm separating the two, although there are alternatives. (Ellis 561, 581; Greenwood 201). Likewise, the produced gases should be monitored to detect inadvertent mixing. (This can occur, for example, if the polarity is reversed-Ellis 585, or by injury to the diaphragm, blockage in the system, or too great current density-Greenwood 202.) . This can be done by sampling the gas and igniting the sample under controlled conditions; they should burn not detonate. (Taylor 73).

From a portability standard, decomposing water with electricity has the advantage that you don't need to transport reactants. As to the weight of the apparatus itself, a Schukert 600 amp electrolyzer holding 50 liters solution and producing 5 m³/24h weighed 220 kg (Englehardt 86). A 110V, 150 amp, 16.5 kw Schmidt system producing 66 m³/24 h weighed 14,000 kg, while a 1.65 kw plant producing one-tenth that weighed 700 kg. (33). Unfortunately, because access to electricity is required, this is not really a method suitable for launch site production. (Batteries are heavy.)

I have gotten mixed signals on the issue of the space requirements for electrolysis. Ells first says that it requires a "relatively large floor space." (570) and then that "for small plants electrolysis has much in its favor." (595; cp. Teel 132). It may depend on the design; Schuckert demands relatively more room (Greenwood 198) while Schmidt is compact (199). Still, there was a portable Schukert generator car weighing in at 2000 kg, used together with a scrubber car of 1700-2100 kg. (Ardery).

The only apparatus for which I have specifics is the Levin generator; 100 will occupy 31 feet by 4.5 feet, and produce 320 cubic feet/hour at 200 amperes. (580). With normal room height, they can be installed in two tiers.

But an electrolytic cell can be very small. With 12.2 watts of solar-based electricity, a modern homemade cell in a 3.5"x5.5"x1.5" plastic container produced 0.399 milliliters/second hydrogen. (Businelli). So the real question is, what is the required cell volume to achieve the desired production rate?

One nice thing about electrochemistry is that you can predict performance. A chemist would expect that 96,500 coulombs (ampere-seconds) of electricity would liberate 1 gram of hydrogen and 8 grams of oxygen, those being the "equivalent weights" (ionic weight/ionic charge). So one ampere-hour produces 0.03731 gram-equivalents, which works out as 0.01482 cubic feet of hydrogen at STP (0^oC, 760 mm Hg), 0.00741 cubic feet oxygen. At 20^oC we do better; 0.01585 of hydrogen and 0.00792 of oxygen. (Taylor 103). The current supplied is typically 200-600 amperes. So, if the current were 400 amps, production would be 5.93 cubic feet hydrogen and 2.96 cubic feet oxygen per hour. (Ellis 536).

Teed (39) considered electrolysis to be suitable only for production of up to 1000 cubic feet hydrogen/hour.

In theory, the required voltage is 1.23, but because of secondary effects (overvoltage) it will probably be found that 1.7 volts are needed for continuous decomposition of water. (Taylor 104; Ellis 536). However, the diaphragm will tend to increase the resistance of the cell, necessitating a voltage of 2-4 volts. (106). As a result, energy efficiencies are in the 50-60% range. (Engelhardt 18, 20, 31).

The first electrolytic oxygen generator constructed for laboratory purposes was that of D'Arsonval (1885), and the first large scale apparatus was that of Latchinoff (1888). (Taylor 108). The first with significant industrial adoption was probably Schmidt's (1899), which produced 99% pure hydrogen and 97% pure oxygen. (Engelhardt 31).

2002McGHEST says that "although comparatively expensive, the process generates hydrogen of very high purity (over 99.9%). However, I think it's a mistake to count out the electrolytic process. Water, of course, is cheap, so the main expenses are those of providing electricity, and separating out the oxygen.

1890-1910 prices for electricity ran around 0.25 cents/kwh for hydroelectric and 1.25 for coal-fired steam plants. (Engelhardt 17). (Ellis 538 assumes 1 cent/kwh, and 569 quotes prices of 3-4 cents in New York City and 0.5 cents in South Chicago.)

Chances are that the recovered oxygen can be sold, thus defraying at least some of the production costs. In fact, the zeppelin hydrogen produced in 1934-38 was a byproduct of the electrolytic production of oxygen. (Dick 193). in 1904, oxygen sold for $1/m³ and hydrogen for $0.3125. (Engelhardt 40).

Bear in mind that "a normal military balloon requires, in order to be filled in twenty-four hours, a plant of about 200 kilowatts." An airship requires a lot more hydrogen than that.

Still, in 1904, the Italian, French and Swiss armies all relied on electrolytic hydrogen. (123).

In 2004, the average cost of electricity in America was 5 cents/kwh and at that price, with 80% electrolysis efficiency and 90% compression efficiency, the power cost for compressed electrolytic hydrogen was $2.70/kg. (Doty).

The higher the temperature, the less electrical energy is needed. If heat is cheaper than electricity, then higher operating temperatures are desirable. (Kirk-Othmer 13:868).

Electrolysis of Alkali. Historically, the first electrolytic hydrogen was a byproduct of the processing of brine to yield sodium hydroxide (caustic soda):

2Na⁺ + 2Cl^- + 2H₂O -› 2NaOH + H₂ + Cl₂

With 100% current efficiency, each ampere-hour would produce 1.322 grams of chlorine, 1.491 grams of sodium hydroxide and 0.0373 grams of hydrogen." (Actual current efficiencies were 90-98%.) The caustic soda may be used to make soap, and the chlorine bleach, and of course there are other uses, too. (Taylor 120). At 15^oC, each ton of salt electrolyzed produces 72320 cubic feet hydrogen. Hydrogen purity is 90-97%. (Greenwood 203). Naturally, you want to prevent intermixing of hydrogen and chlorine after production.

In 1904, this was the method used to produce hydrogen for German army balloons. (Englehardt 123).

Water Thermolysis. The thermal decomposition of water requires temperatures in excess of 2000^oK, and of course reactor materials that can tolerate the temperature. (Yurum 24).

Splitting Hydrogen Sulfide. The use of hydrogen sulfide as a source of hydrogen has been proposed, but not commercialized. One possibility is to react it with iodine, producing sulfur and hydrogen iodide, and then decompose the latter. Another is to react it with methane, forming hydrogen and carbon disulfide. (Kirk-Othmer 13: 874). These methods probably do not appear in Grantville literature.

Thermal Decomposition of Hydrocarbons. When exposed to sufficient heat (1200-1300^oC for methane, 500^oC for acetylene), hydrocarbons dissociate into their component elements. (Ellis 471).

The Rincker-Wolter system is of some interest because they started with oils and tars, and the demand for tar in163x is limited. The required temperature was 1200^oC for the hydrogen to be of acceptable purity. In 1912, a plant producing 3500 cubic feet/hour would cost $2575 plus "erecting expenses," and with the oil at 4 cents/gallon, the hydrogen cost would be $1.75/1000 cubic feet. (Ellis 473ff). A semiportable plant with such capacity has been successfully mounted on two railway trucks. Greenwood 193 reports a cost of 550 pounds sterling for the plant and 2s/6p to 4s/0p per 1000 cubic feet.

A variation on this is the Carbonium process; acetylene gas is compressed to two atmospheres and exploded by an electric spark, yielding carbon (deposited as lamp-black) and high purity hydrogen. You need an explosion chamber, and the lamp black is scraped off the walls. If there's a market for the lamp black (one kg per cubic meter of hydrogen), this method can be advantageous. (Ellis 473). The good news about the process is that it was used to supply hydrogen for the zeppelins at Friedrichshafen. The bad news is that the factory was destroyed by an explosion in 1910! Before this slight mishap, the cost of production was 4 shillings per 1000 cubic feet. (Greenwood 192).

Catalytic steam-hydrocarbon reforming. Per McGHEST2002, volatile hydrocarbons (from natural gas) are reacted with steam over a nickel catalyst at 700-1000^oC, forming hydrogen and carbon monoxide, the latter being converted to carbon dioxide by reaction with water at 350^oC over an iron oxide catalyst. If the hydrocarbon were methane (which has the highest hydrogen:carbon ratio), the first reaction would be

CH₄+H₂O-›CO+3H₂.

The encyclopedia notes that carbon dioxide may be removed by scrubbing with aqueous monoethylamine. However, there's a much easier method; pass the gas mixture through water under high pressure; the carbon dioxide reacts with water to form carbonic acid and dissolves; the hydrogen doesn't dissolve and bubbles to the surface.

Even with these hints, the method may take a while to get working. In the old time line, experiments began in 1912, but the first real success, with methane over a nickel catalyst, came in the 1920s. It wasn't commercialized until 1931. (Smil 113). Note that the reforming catalyst isn't necessarily the simple metal; the 1962 ICI process used nickel-potassium oxide-aluminum oxide (Weissermel 18).

In the 1632 universe, the likeliest source of the volatile hydrocarbons would be coal gas, but natural gas would also be an option. However, we do have to find the right catalyst, and the feedstock may include substances (sulfur, chloride) that poison the catalyst.

Immediately prior to the RoF this was the dominant method of producing hydrogen. the Kirk-Othmer Encyclopedia of Chemical Technology reports that it had a thermal efficiency of 78.5%, versus only 27.2% for water electrolysis, and a net hydrogen production cost of $7.19 (1985 dollars)/100 m³, versus $22.63 for electrolysis. (13:853). The theoretical energy consumption is 300 BTU/scf hydrogen, and a typical one is 320. If the natural gas price is $4/million BTU, feedstock and utility costs are 65% total operating costs. (Udengaard).

Catalytic steam-methanol reforming. This is a related process:

CH₃OH-›CO+2H₂.

Steam reacts with the carbon monoxide to form carbon dioxide and more hydrogen. The process has been proposed for modern field use, with a one ton trailer-mounted generator producing 150 cubic feet/hour with fuel consumption of just over one gallon/hour. (Philpott).

In the old time line, it had higher operating costs but lower fixed costs than the hydrocarbon-based scheme. (Blomen, 150). Other advantages are that methanol is free of sulfur and the reaction can be run at a lower temperature (300°C). (Liu 65). However, the problem is that experimentation will be needed to find appropriate catalysts (likely to be copper, zinc oxide or palladium-based).

Decomposition of Ammonia. The first problem is producing the ammonia. Nowadays it's made by the Haber process from nitrogen and hydrogen, but obviously if our goal is hydrogen, we are taking a different route. There is ammonium carbonate in New World guano deposits, and ammonium sulfate is a potential byproduct of the manufacture of boric acid in Tuscany. We also must determine the decomposition conditions. Ammonia can be decomposed by heat alone but a catalyst helps. (Lunge 580ff) Ammonia is another possible target for catalytic reforming. (Udengaard).

Fermentation. The Weiszmann process for the manufacture of acetone and butyl alcohol by fermentation of starchy foods (maize, potatoes) also produces hydrogen and carbon dioxide in equal volumes; 5.5 cubic feet of mixed gas per pound of maize fermented. (Taylor 166). Both acetone and butyl alcohol are quite important industrial chemicals, and so the sale of hydrogen needs to only cover the cost of its separation from carbon dioxide. The real problem is isolating the necessary fermentation organism.

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Disaster Scenarios. As the hydrogen is produced, it mixes with any air that is present, soon creating flammable or even explosive mixtures. Ideally, several volumes of an inert gas (carbon dioxide, nitrogen) or liquid (water) are run through the production chamber first, to drive out the air. Also watch out for leaks from the gas hoses.

If the reagents are stored close together, and their containers are ruptured, an uncontrolled reaction can occur.

Some of the reactions are exothermic, so even if the reaction is in the proper vessel, the temperature has to be monitored.

Comparative Operating Costs

I was able to find some comparative operating cost data on the different production processes. Some sources include labor and overhead (interest and depreciation on fixed costs), and others don't.

Figure that one 1900 US dollar is 4.2 contemporaneous British shillings, or 0.5 1632 shillings if deflated based on Allen's laborers' wage rates, and 1.25 if using Allen's London CPI. (Two shillings is equivalent to one Dutch guilder. ) That same 1900 dollar is $19.57 in 2000 if inflated using the Sahr CPI.

The NTL economy in 1635 is going to be very different than that of pre-RoF Europe, and also different from that of OTL early-twentieth century Europe. Hence, be cautious about putting a lot of faith on cost conversions. It's probably better to use the table to get a sense of relative rather than absolute costs, but even that's dangerous; individual inputs (e.g., electrical energy) could be cheaper or more expensive in the new universe, even different from one region to another.

It's interesting to note that, depending on who you ask, electrolytic hydrogen is cheaper (Roth), more expensive (Ellis/Sander), or the same cost (Greenwood) as hydrogen from the steam-iron plant. I suspect that it turns on what the assumed cost of power is. Bear in mind that nowadays, electrolytic hydrogen is much more expensive than hydrogen from steam reforming.

This cost data (Tables 5A, 5B) is not available in Grantville, but they can calculate the materials requirements and cost them out separately.

(1) materials only, steam and water treated as free; refrigeration power cost of 60 cents/1000cf.

(2) Ellis 595, mostly based on Sander; additional prices of 18.75 for silicol (p523) and 32-38 for hydrogenite (521ff). Cp. 462ff for fractional refrigeration, 445, 458 for Griesheim-Elektron 472 Carbonium.

(3) Greenwood 213, 234. Assumes power cost of 0.25p/kwh.

Ellis (537ff) breaks down the operating cost for electrolytic production of 632 cubic feet compressed hydrogen/hour (4,550,400 cubic feet/year of 300 workdays, 24 hours/day) and half that of compressed oxygen as follows:

Hydrogen Purification

I talked about purification of carbon monoxide in the section on "water gas." In essence, carbon monoxide may be removed by treatment with cuprous chloride, or hot soda lime, caustic soda, or calcium carbide, or by liquefaction. Carbon dioxide is eliminated by washing with slaked lime, or water under pressure. Bog iron ore will extract hydrogen sulfide. (Greenwood 211ff).

Hydrogen Transport

Generally speaking, in the early-twentieth century, hydrogen was compressed for shipment to industrial customers. In 1904, figure that a gas compressor for compressing 100 cubic meters of hydrogen every 10 hours cost $1000, and a second compressor for the associated 50 cubic meters oxygen would be $625. (Engelhardt 39). Ellis (556) estimated that compressors for a 10 cubic meter/hour hydrogen system would be $2850.

According to Ellis (538), an electrolytic hydrogen plant would require 4 kilowatt-hours for compression of 632 cubic feet (17.9 cubic meters) hydrogen to 300 psi (20 atmospheres), and 12 kilowatt-hours to compress 316 cubic feet oxygen to 1800 psi. Engelhardt (113) says that for compression to 100-120 atmospheres, the total power required would probably be about 4 kwh for 1 m3 hydrogen and 0.5 oxygen.

The tanks were also a significant expense. The plant had to purchase enough so that it didn't have to wait for empties to be returned in order to keep up with demand. The steel tanks weighed 10 kilograms per cubic meter gas held, and a 40 kg tank cost $11.75 in 1904. (Englehardt 118ff).

You have to be careful; don't use the same compressor alternately for hydrogen and oxygen, and don't use a former oxygen cylinder to carry hydrogen, or vice versa, without being sure that you completely removed the old gas. (Ellis 592).

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An alternative to compression is liquefaction. Hydrogen was first liquefied in 1898. Liquefaction requires bringing the hydrogen to a pressure above its critical pressure (12.8 atmospheres), and then cooled below its critical temperature (-239.95^oC). Keeping it liquid requires keeping it pressurized and cold, even in transport. And if you fail, well, remember that liquid hydrogen is a rocket fuel. I think it will be decades before liquid hydrogen appears in the new time line.

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Since military balloons had to be launched near the front line, where transportation options were likely to be limited, the tanks were moved by a variety of means. The first use of compressed hydrogen in warfare was possibly in the British expedition to the Sudan (1885); each camel carried two 66 pound cylinders, each carrying 140 cubic feet (after expansion) of gas. (AGLJ) In the Boer War, fifty horses were needed to transport cylinders (weighing 1 pound/cubic foot hydrogen) enough to fill a 14,000 cubic foot balloon. (Greenwood 223). Later, the Germans used railway wagons that weighed 30 tons and carried almost 100,000 cubic feet hydrogen. (233) The American military neglected the balloon after the Civil War, but in 1891-3, the Signal Corps decided to add a tethered balloon and fill it with hydrogen from pressurized (120 atmosphere) cylinders. (Crouch 519ff).

Airships have much greater mobility than military balloons, so we aren't limited to "front line" options, but the rail network is much less developed in the 1632 universe.

The total cost of compressing and shipping hydrogen to a remote airship facility can be high. For 12.5 cubic meters hydrogen, compressed and shipped 300 miles, and empties returned, Schmidt estimated (1900) 29.5 cents to produce the gas, 2.5 to compress it, 16.25 as interest on the purchase cost of the tanks, 2 for labor, and 62.5 for the two-way freight, for a total of $1.13-9 cents/m³. (Englehardt 129).

In 1915, Fourniols compared the cost of producing hydrogen at a cheap-to-operate hydrogen plant and shipping it in compressed form, to generating it on site using the hydrolith process. The former produced hydrogen at a cost of only 0.4 francs/cubic meter. But compression and transport of 50,000 cubic meters for an unstated distance increased the cost from 20,000 francs to 960,000. In contrast, the same amount of hydrogen could be produced by the field process for 324,000 francs, of which only 40,000 was transport-related (carriages for the apparatus and reagents). (Ellis 534).

At some point, high pressure hydrogen pipelines, like the early-twentieth century one from Griesheim to Frankfurt, might reduce transport costs. (Ellis 440).

There are two complications with storing hydrogen; its great capacity for diffusion through other materials, and its ability to embrittle metals, include steel (Kirk-Othmer 13:851). That may limit the useful life of storage cylinders.

Hydrogen Recycling

The contents of a gas cell will become corrupted as hydrogen escapes and, more slowly, air enters. The hydrogen in this "spent gas" may be recovered for re-use by an adaptation (Greenwood 233) of the Linde-Frank-Caro liquefaction method used to separate hydrogen from carbon monoxide in the water gas processes.

Hydrogen Testing

To avoid explosions and fire, and maximize lifting power, it's important to know how pure the produced hydrogen is, and what other gases it's contaminated with. Hydrogen may be measured by combustion with excess oxygen, or by measurement of the thermal conductivity of the gas. Carbon monoxide will blacken paper moistened with palladium chloride, or it can be quantified by measuring the carbon dioxide formed by its reaction with hot iodine pentoxide. Carbon dioxide, in turn, is detected by its reaction with lime water or barium hydroxide. (272). Oxygen is revealed by blueing if the gas is bubbled through a colorless cuprous salt solution.

We can measure arsenic with the "mirror test" beloved of early detective stories, and hydrogen sulfide by its reaction with a lead acetate paper. (Greenwood 235ff, 254, 272; Taylor 193ff).

I leave it up to the reader to determine the extent to which these detection methods would be known in Grantville Literature, and how soon the necessary reagents and apparatus could be produced.

Conclusion

In the 1630s, I believe that electrolysis, whether of water or alkali, should be the dominant method of hydrogen production in Grantville itself. There's ready access to electricity, which, for the reasons I set forth in Cooper, "Aluminum: Will O' the Wisp?" (Grantville Gazette 8), should be relatively cheap for several years despite its ultimate dependence on burning coal.

And we don't have to worry about compressing the gas if the airship station is in Grantville. If we electrolyze water, we have the further advantage that we are producing oxygen (which itself is valuable) and the hydrogen is going to be of extremely high purity (at least if we use distilled water).

Otherwise, the practicality of electrolytic hydrogen will depend on whether electricity is available. That in turn first requires either the proximity of a river with a suitable gradient and flow rate (for hydroelectric power), or of fuel (coal, oil, wood, etc.) to burn. And secondly, you need the turbine for converting the kinetic energy of falling water, or the boiler and steam engine (piston or turbine) for converting the chemical energy of the fuel. I considered this, in a rail electrification context, in Cooper, Locomotion: The Next Generation (Grantville Gazette 34).

Unfortunately for Copenhagen, which in canon is a leader in airship development, Denmark is not well suited for electric power generation of any sort. As we know, Marlon Pridmore chose to rely on the steam-iron process. However, generating steam requires heat, and plainly the Danes are burning some kind of fuel to do it. With no waste, you need nine grams of water to make one gram of hydrogen (0.42 cubic feet), and to make several hundred thousand cubic feet of hydrogen is going to require a heck of a lot of fuel. My guess is that the Danes will establish a big steam-iron plant that is on the Copenhagen-Venice route and near to a coal field or at least has ready river or rail access to a coal field. Hannover is a possibility, but coal would probably be cheaper near Cologne, and they could add service to Amsterdam and Hamburg. The airship would make a "pit stop" when its gas cells were getting dicey.

I think that there will also be some experimentation, by would-be airship powers, with the steam-carbon and steam-hydrocarbon processes. The former uses coal, which is abundant in western Europe, and the latter can make do with petroleum fractions that aren't useful as vehicle fuels. And of course, if you have carbon or hydrocarbon for use as a reactant, you can presumably use some of it as fuel for steam-making.

We know that there is going to be rapid scale-up of both iron and sulfuric acid production, which will provide some initial impetus to explore the potentialities of the wet method. If the Civil War buffs in Grantville have particulars of Lowe's hydrogen generator, that will also give it a boost. However, acid-iron has too many disadvantages to be attractive in the long-term.

The search for oil will inevitably result in the discovery of natural gas reservoirs, like that in the Grantville area. The pyrolysis of coal, to produce organic chemicals such as benzene, will produce coal gas as a byproduct. The accelerated development of chemical knowledge will lead to the relatively early discovery of catalysts suitable for reforming methane (and other volatile hydrocarbons) from natural gas or coal gas. This will facilitate stationary hydrogen production.

Of the classic field methods, I think silicol will be the first one to become practical in the 1632 universe. A crude silicon can be made easily enough, and there is going to be demand for ferrosilicon by the steel industry and that will help bring costs down.

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