AMMONIA WITH CARBONIC ACID. 101 



of the carbonate of barytes is expelled ; the strongest heat that an 

 alcohol lamp, with double current of air, is capable of producing, 

 may be applied without occasioning any loss. 



A solution of chloride of calcium cannot be employed with the 

 same advantage as one of chloride of barium for precipitating the 

 carbonic acid. The carbonate of lime, it is true, does not form so 

 bulky a precipitate as the carbonate of barytes ; but a portion of 

 the precipitate adheres so firmly to the sides of the vessel, that it 

 is impossible to separate it completely by mechanical means. 

 The heating of the carbonate of lime has also its disadvantages, 

 as it then loses a portion of the carbonic acid. 



In determining the carbonic acid in the neutral combinations, 

 it was precipitated by chloride of barium without any addition of 

 ammonia. In this case also the whole must be left to stand for 

 some time after precipitation before the carbonate of barytes is 

 filtered. When the solution of the neutral carbonate of am- 

 monia is very weak, no precipitate is produced for some time by 

 the chloride of barium, which is characteristic of the neutral salt. 

 The liquid separated from the carbonate of barytes is then satu- 

 rated with ammonia, in order to see whether any small precipi- 

 tate would follow, which in general was the case ; it was occa- 

 sioned by the impossibihty of obtaining the carbonate of ammo- 

 nia always perfectly neutral. This precipitate, although filtered 

 perfectly without exposure to the air, was nevertheless always 

 more considerable than it should have been, and the amount of 

 carbonic acid in the salt thus appeared to be greater than it really 

 was. 



The second method of determining the carbonic acid was by 

 measuring it in the state of gas. A weighed quantity of 

 the salt was decomposed in a graduated cylinder under mercury 

 by means of mvu-iatic acid, in which shortly previous to the ex- 

 periment some carbonate of ammonia had been chssolved, in 

 order to saturate it with carbonic acid. When the salt could 

 only be employed in the form of powder, it was wrapped up in 

 bibulous paper. This method, however, gave, even when all 

 circumstances had been most carefully taken into consideration, 

 less accurate results than by means of the carbonate of barytes. 

 In general I obtained somewhat less carbonic acid than I ought.. 

 As, however, it is more quickly and easily performed, I have 

 chiefly made use of it to ascertain to what known combinations 

 of ammonia and carbonic acid any salt might belong. 



