Carbonic Acid and Ammonia. 249 



tilled water, and precipitating by nitrate of silver ♦. I may re- 

 mark, that I had previously ascertained, by a very careful trial, 

 that salammoniac, when exposed for several hours on a steam- 

 bath, appears to suffer no more loss than may be attributed to 

 the dissipation of a very little adhering or hygrometric water -f- ; 

 and, also, that, at the same temperature, after two or three hours' 

 exposure of the salt, all excess of acid is entirely dissipated J. 



To shew the degree of accuracy this method admits of, ap- 

 plied to minute quantities, I may mention the results of two 

 analytical trials which I made (and they were not the only ones) 

 before I gave it my confidence ; one on the proportion of car- 

 bonic acid in carbonate of lime, which may be considered as 

 pretty well determined ; the other, on the composition of salam- 

 moniac. 



A minute fragment of pure Carrara marble, equal to 1 grain 



• I had recourse to this method, from not obtaining uniform results when 

 I attempted to ascertain the exact proportion of ammonia, either by the quan- 

 tity of acid, of a given strength, required to neutralize the alkali, or from the 

 volume of gas disengaged decomposing the salt by quicklime, according to 

 Dr Ure's plan ; or, after Mr Richard Philips*, by the quantity of carbonate 

 of lime precipitated by the salt from the neutral muriate of lime. This last 

 mentioned method, in my hands, has proved the least satisfactory of any that 

 I have tried, the variations of results having been very great, according to in- 

 cidental circumstances of temperature and of strength of solution, &c. The 

 effect of temperature is most remarkable. It is necessary to employ heat, to 

 separate the whole of the carbonic acid gas, and insure the precipitation of 

 the carbonate of lime. The difficulty is to effect this without a loss of am- 

 monia ; for, if either the sesquicarbonate or bicarbonate in solution is poured 

 into a hot neutral solution of muriate of lime, at 170* and upwards, there is a 

 strong ammoniacal odour produced, at the same time that there is a violent 

 effervescence from carbonic acid gas liberated, and a rapid precipitation of car- 

 bonate of lime ; or, taking the reverse, if a mixture of carbonate of lime and 

 solution of muriate of ammonia is heated to the same degree, a mutual decom- 

 position of the two commences, as is indicated by the odour of the volatile al- 

 kali which is perceived. 



-|- 5 grains of salammoniac from a translucent mass, reduced to powder, afler 

 exposure on the steam-bath for five hours, were reduced to 4.98 grains. When 

 first placed on the bath, a faint peculiar odour was perceptible on very near 

 approach, as if an extremely minute quantity of the salt was raised with the 

 very diluted aqueous vapour. 



X 5 grains of the same salt were dissolved in very dilute muriatic acid, 

 slowly evaporated to dryness, and then kept on the steam-bath for about two 

 hours afler acid fumes had ceased to be perceived. The loss in this instance 

 was precisely the same as in the first, namely .02 grains. 



