Grantville Gazette 38

[KO] Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., Vol. 13 (1995) and 20 (1996).

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Hydrogen: The Gas of Levity

Iver P. Cooper

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