In olden times ammonia was principally obtained from animal matter, originally in Egypt by the distillation of camel dung, later on from urine, and from the distillation of bones and horn. The quantity so obtained was very small and the products very expensive. The introduction of coal gas for illumination gave us a considerable and constantly increasing supply of ammonia as a by-product of the gas manufacture, and until recently all practical efforts to increase our supply of ammonia were directed toward collecting and utilizing in the best possible manner the ammonia so obtained. The immense extension of the coal gas industry all over the world has in this way put us into possession of a very considerable amount of sulphate of ammonia, amounting in Europe now to 140,000 tons per annum. In recent years this has been augmented by the ammonia obtained by the distillation of shale, by the introduction of closed ovens for the manufacture of coke, combined with apparatus for condensing the ammonia formed in this manufacture, and also by the condensation of the ammonia contained in the gases from blast furnaces working with coal. But all these new sources have so far added only about 40,000 tons of sulphate of ammonia to our supply, making a total of 180,000 tons per annum, of which about 120,000 are produced in the United Kingdom, while we still import 650,000 tons of nitrate of soda, equivalent to 500,000 tons of sulphate of ammonia, to make up our requirements.
Many processes have from time to time been proposed to obtain ammonia from other sources. The distillation of turf, which contains upward of 3 per cent. of nitrogen, has received much attention, and a large number of inventors have endeavored to produce ammonia from the nitrogen of the air; but none of these processes has to my knowledge been successful on a manufacturing scale.
My attention was called to this subject at an early part of my career. Already, as far back as 1861, I undertook experiments to utilize, for the production of ammonia, waste leather, a waste material of animal origin at once abundant and very rich in nitrogen, containing from 12 per cent. to 15 per cent. of this element. Distillation in iron retorts yielded about half the nitrogen of this material in the form of ammonia, the carbon remaining in the retorts containing still from 6 per cent. to 8 per cent. Distillation with a moderate quantity of hydrate of lime increased the yield of ammonia only by 1 per cent. to 1½ per cent. A rather better result was obtained by distilling the ground residual carbon with hydrate of lime, but this operation proceeded very slowly, and the total yield of ammonia still remained very far below the quantity theoretically obtainable, so that I came to the conclusion that it was more rational to utilize the leather, reduced to powder by mechanical means, by mixing it directly with other manures.
A few years later I became connected with a large animal charcoal works, in which sulphate of ammonia was obtained as a by-product. Here again I was met with the fact that the yield of ammonia by no means corresponded with the nitrogen in the raw material and that the charcoal remaining in the retorts contained still about half as much nitrogen as had been present in the bones used.
From this time forward my attention was for many years given exclusively to the soda manufacture, and it was only in 1879 that I again took up the question of ammonia. I then determined to submit the various processes which had been proposed for obtaining ammonia from the nitrogen of the air to a searching investigation, and engaged Mr. Joseph Hawliczek to carry out the experimental work.
These processes may be broadly divided into three classes:
(1.) Processes which propose to combine nascent hydrogen with nitrogen at high temperatures or by electricity, with or without the presence of acid gases.
(2.) Processes in which nitrides are first formed, from which ammonia is obtained by the action of hydrogen or steam.
(3.) Processes in which cyanides are first formed and the ammonia obtained from these by the action of steam.
We began with an investigation of those processes in which a mixture of steam and nitrogen or of steam and air is made to act upon coke at a high temperature, sometimes in the presence of lime, baryta, or an alkali, sometimes in the presence of hydrochloric acid.