In his autobiography 'Slide Rule" Nevil Shute says quite a lot about the problems of filling the gas bags of the R100. He tells us that the volume of hydrogen required was a little over five million cubic feet (and cost about £800) but the only thing mentioned about its production is that there was a gas plant just outside the shed and the gas was conveyed in a gas main which ran beneath the ground to points immediately below the ship.
Barry Countryman describes the filling operation in his book "The R100 in Canada". The gas was produced by the "Silicol" process, which is described later on. The gas plant had two 30,000 cu.ft per hour generating units and the gas went directly into the airship. There was no gas holder, so any interruption in the filling process could cause difficulties and wastage. To overcome the problem of the newly generated gas going into the ship hot, a trench containing about 100yds of gas main was flooded and a continuous supply of water was run through it to keep the temperature down to about 60 F. The record day's production of hydrogen was 500,000 cubic feet. Within ten days 14 gas bags were inflated. Number 15 was inflated just before R100 was ready for her engine trials. These Nevil Shute does describe in graphic detail in Slide Rule when the "airborne" R100 had to be moored inside the huge shed with the engines running !
Thanks to some help from the Airship Trust who lent me some Hydrogen Manuals I can describe the silicol process as follows. Powdered ferrosilicon is fed in a controlled manner into a closed stirred tank containing a very hot, strong solution of caustic soda. The ferrosilicon reacts rapidly with the caustic soda, producing a mixture of steam and 99% pure hydrogen. Usually the gas is passed through cold water in a "scrubber" to condense the steam, collect the hydrogen and remove some of the (poisonous) impurities. The chemical reaction produces a lot of heat, which is used to keep the temperature of the tank at around 115 C. A residue consisting mainly of sodium silicate ("water glass") is left in the liquid in the tank. When the batch of caustic soda has become exhausted, the tank must be drained as soon as possible, otherwise the residue will solidify in the tank.
Barry Countryman finally tells us that due to valve testing, diffusion, losses from air temperature and pressure variations, an airship required at least 50% more hydrogen than her maximum capacity. Prior to the R100's first flight, water, 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*.
Rev. John B. Wilcox
*? his calculations