204 SECONDARY PRODUCTS. 



skimmed off. The quantities of these will constantly vary, and will depend 

 upon the care with which the liquor has been taken from the well. 



The water holding ammonia in solution is now decanted, by means of a 

 siphon, from the tarry deposit into leaden evaporating pans ; sulphuric acid 

 is then added, so as to convert the sesquicarbonate and hydrosulphate into the 

 sulphate of ammonia. 



During this operation a large quantity of sulphuretted hydrogen is given off, 

 and is conducted to the ash-pit of one of the furnaces, under the evaporating 

 pans, to be consumed, and prevented from extending an injurious influence 

 on the health of the workmen. The saturated liquor is evaporated until a 

 strong pellicle is formed on the surface ; then decanted into shallow vessels, 

 and allowed to cool and deposit its crystals. 



If it be considered necessary further to purify this salt, it may be accom- 

 plished by heating it, to drive off the remaining portion of bituminous matter ; 

 but then it is essential that the salts contained in the liquor be converted into 

 the bisulphate, otherwise one equivalent of ammonia would be lost by sub- 

 limation. 



In some manufactories the liquor is rectified previous to the addition of the 

 acid ; for this purpose it is run into a boiler (such as those used for steam- 

 engines), connected by a long iron pipe, with a closed receiver; on applying 

 heat, the ammoniacal products are evolved, and condensed in the receiver and 

 connecting-pipe. To the distilled liquor, containing a large quantity of ammo- 

 nia, the acid is now added, and the subsequent operations proceeded with. 

 This, however, is a process not generally recommended, since the sesquicar- 

 bonate of ammonia is not volatile at the temperature of boiling water, but is 

 decomposed, free ammonia escaping, while the neutral carbonate remains 

 dissolved. 



The sulphate of ammonia, prepared by the above process, is tolerably pure, 

 and may be used for the purpose of obtaining the carbonate and muriate, the 

 salts most used in the arts. If for the former, a portion of carbonate of lime 

 (common limestone or chalk) is added to the sulphate, well triturated with it, 

 and the mixed mass sublimed in earthenware vessels. If the muriate is re- 

 quired to be formed, common salt is substituted for the carbonate of lime, and 

 the mixture similarly treated. 



