Manurial Properties of Clay from Gas- Works. 301 



as great as the former,* the circumstances under which it promotes 

 growth are precisely similar to those in the other case. Yet if 

 the substances contained in farmyard manure and those contained 

 in guano be placed side by side in parallel columns, none but 

 chemists would recognise the same fertilizing elements in the 

 srrand total of such dissimilar substances. 



Coal is commonly regarded as the remains of an extmct vege- 

 tation, whicli has been subjected to slow oxidation under enor- 

 mous pressure. It contains about 175 per cent, of nitrogen, 

 equal to 2' 125 of ammonia, while farmyard dung, in its ordinary 

 condition, contains about "64 per cent, of nitrogen, equal to am- 

 monia -78.1 The latter is equal to 14-3 lbs. of nitrogen per ton, 

 or 17*4 lbs. of ammonia, while the former equals 392 lbs. of nitro- 

 gen, or 47*6 lbs. of ammonia. If coal would decompose readily, 

 we need only lay it upon our fields to give them all the elements 

 of the highest fertility. But inasmuch as it will lie almost unde- 

 composed for scores of years, its treasures are locked up, and some 

 process of disintegration must be resorted to before they are avail- 

 able. Burning is a process of this kind, but so enormously wasteful 

 as to be intolerable were it not that the formation of manure is a 

 subordinate, and the production of heat the principal object sought 

 by the combustion. The soot deposited in our chimneys is a 

 valuable fertilizer, containing variable quantities of different ingre- 

 dients, of which the most important to agriculture is sulphate of 

 ammonia. Johnston found 35 per cent, of this substance ; but I 

 have never met with so large a quantity, and suspect that 12 per 

 cent, is far nearer the average. 



Distillation, as practised at our gas-works, is also a means of 

 disintegration, in which case so much nitrogen is volatilized, that 

 nearly all the salts of ammonia in commerce are derived from 

 this source. The ammonia produced is carried down with the 

 condensed tar and water produced in the distillation, and no 

 advantage to agriculture appeared likely to result from attempts 

 at improvement here. No attempt, therefore, was made to touch 

 what was known and available, but it was from the gas after 

 deposition of tar and ammonia that a valuable addition to our 

 known fertilizers was sought and discovered. Distillation does 

 not volatilize the whole, or nearly the whole, of the nitrogen ot 

 coal and ammimia, but converts a large part of it into other com- 

 pounds, which have long been the pests of gas- consumers, and 

 which have a high value to the farmer. Moreover, much of the 

 ammonia produced was not removed by the ordinary means of 

 purification, but passed on with the gas to the destruction of 



* Guano = 14/. per ton ; farmyard dung = 5s. per ton ; 5s. X 56s. = 14Z. 

 t R. A. Society's Journal, vol. xvii., p. 194. ^ 



