cost of manufacture depends mainly upon the yield of ammonia, as the expenses remain almost the same whether a large or a small amount of ammonia is obtained; the only other item of importance is the quantity of steam used in the process.  We found the yield of ammonia to vary with the temperature at which the producer was working, and to be highest when the producer was worked as cool as was compatible with a good combustion of the fuel.  The temperature again depended upon the amount of steam introduced into the producer, and of course decreased the more steam increased.  We obtained the best practical results by introducing about two tons of steam for every ton of fuel consumed.  We experimented upon numerous kinds of fuel, common slack and burgy of the Lancashire, Staffordshire, and Nottinghamshire districts.  We found not much difference in the amount of nitrogen contained in these fuels, which varied between 1.2 and 1.6 per cent., nor did we find much difference in the ammonia obtained from these fuels if worked under similar conditions.  Employing the quantity of steam just named we recovered about half the nitrogen in the form of ammonia, yielding on an average 0.8 per cent. of ammonia, equal to 32 kilos, of sulphate per ton of fuel.  In order to obtain regular results we found it necessary to work with a great depth of fuel in the producers, so that slight irregularities in the working would not affect results.  Open burning kinds of slack do of course work with the greater ease, but there is no difficulty in using a caking fuel, as the low temperature at which the producers work prevents clinkering and diminishes the tendency of such fuels to cake together.

The quantity of steam thus required to obtain a good yield of ammonia is rather considerable, and threatened to become a serious item of expense.  Only one-third of this steam is decomposed, in its passage through the producer, and two-thirds remain mixed with the gases which leave the producer.  My endeavors were consequently directed toward finding means to recover this steam, and to return it to the producers, and also to utilize the heat of the gases which leave the producers with a temperature of 450 deg. to 500 deg.  C., for raising steam for the same purpose.  The difficulties in the way of attaining this end and at the same time of recovering, in a simple manner, the small amount of ammonia contained in the immense volume of gas we have to deal with, were very great.  We obtain from one ton of coal 160,000 cubic feet of dry gas at 0 deg.  C. and atmospheric pressure.  The steam mixed with this gas as it leaves the producer adds another 80,000 cubic feet to this, and the large amount of latent heat in this quantity of steam makes the problem still more difficult.  The application of cooling arrangements, such as have been successfully applied to blast furnace gases, in which there is no steam present, and which depend upon the cooling through the metallic sides of the apparatus, is here practically out of the question.  After trying a number of different kinds of apparatus, I have succeeded in solving the problem in the following way: