PHOSPHATE OF AMMONIA. 85 



161. Phosphate of ammonia may be formed by 

 adding a solution of ammonia, or its carbonate, to 

 phosphoric acid (194); it is very soluble in water, 

 and decomposes when heated, the ammonia passing 

 off in the gaseous state, and leaving the phosphoric 

 acid pure. A rough salt may be made by mixing 

 the impure phosphoric acid obtained by acting on 

 bone, earth, by oil of vitriol, with gas liquor, and 

 evaporating the solution ; it is then, however, apt to 

 contain lime, tarry matter, and other impurities. It 

 is sometimes employed as a manure (793). 



162. Ammonia often seems to combine with sub- 

 stances for which it really has no affinity : this is 

 merely a mechanical effect. Such substances have 

 the power of absorbing a large quantity of the gas, 

 which is condensed or packed up in the pores of the 

 substahce, but not combined with it, and is ready to 

 be given off again on the application of heat. Thus, 

 freshly burnt charcoal, and, indeed, most porous 

 substances, absorb or condense a large volume of this 

 gas. The value of charcoal as a disinfecting agent, 

 and purifier generally, chiefly depends upon this 

 power of absorbing gaseous matter. But it also 

 possesses bleaching powers. 



163. Ammonia is not the only compound contain- 

 ing nitrogen, which is formed during the decomposi- 

 tion of animal substances ; for although nitrogen and 

 oxygen appear to have no affinity for each other, as 

 they exist together in a state of mixture in the air, 

 and do not enter into combination, yet when a com- 



