220 Composition and Value of Guano. 



monia, it may not be out of place here to state the reasons for the 

 obviously high price of the salts in question. 



We have just now stated that coal-gas, as it is discharged from 

 the mouths of the retorts in which the coal is heated, is unfit for 

 consumption, being contaminated, amongst other things, with 

 hydrosulphate and carbonate of ammonia. To get rid of these 

 compounds, which would render the gas more or less impure, the 

 manufacturer has recourse to some method of purification. For 

 the sulphuretted hydrogen he employs lime, which retains the 

 largest portion of the noxious gas. The ammonia is in great part 

 deposited in the cooling apparatus or condensers. Both of these 

 processes of purification are a source of considerable annoyance 

 and trouble in the preparation of gas, and for the separation of 

 the ammonia in particular the want of some perfect method has 

 long been felt. Many chemical substances have been proposed 

 for the purpose, but as yet no method has been found which 

 should both purify the gas without injury to its quality and at the 

 same time atford an economical supply of ammonia for agricul- 

 tural purposes. The object in view would, at first sight, appear 

 of most ready accomplishment by means of a mineral acid, so 

 arranged that it should abstract the ammonia from the gas in its 

 passage from the retorts. With this view the gas has been passed 

 through sawdust or other porous substances moistened with sul- 

 phuric acid, by which a perfect separation of the ammonia has 

 been obtained. But, unfortunately, it appears that the success of 

 this process, on the one hand, is entirely neutralized by an un- 

 looked-for objection. It is found that the illuminating power of 

 the gas is very greatly impaired by its contact with the sulphuric 

 acid, a result which has of course led to the abandonment of the 

 method. 



The sulphate and muriate of ammonia of commerce are for 

 the most part made from the ammoniacal liquids of the gas-works ; 

 and to the evaporation and other manipulations necessary to ob- 

 tain the salts in the dry state is chiefly to be ascribed their high 

 price. That such is the case will be clearly seen by examining 

 the composition of these salts. 



Sulphate of ammonia (see note in Appendix) contains, when 

 perfectly pure and dri/y 



Ammonia 22*7 per cent. 



Sulphuric Acid .... 53*3 „ 

 Water 24-0 ,, 



This water is, as the chemical reader would understand, water 

 of composition or crystallization, and its existence is perfectly 

 compatible with the salt being dry. But it is not to be expected 

 that a salt prepared on the large scale should be perfectly pure, 



