Carbotiic Acid and Ammonia, • 247 



made, was heated twelve hours before, above the boiling point 

 of water, and the tubes were filled with it whilst still warm * ; 

 and the gases of known purity, collected in a separate mercurial 

 trough, were dried previous to their combination, — the alkaline 

 gas by means of potassa (kali purum of the shops), the acid gas 

 by chloride of calcium -f*. 



I do not consider it necessary to enter into a minute detail of 

 the experiments made with these precautions. The results ge- 

 nerally were amply confirmatory of M. Gay Lussac*s accuracy, 

 indeed even beyond my expectation, reflecting that the results 

 of the best experiments are only approximations to absolute 

 truth. Thus, in one instance in which IJ cubic inch of ammo- 

 nia was condensed by carbonic acid added in excess, the residual 

 excess of the acid gas did not differ from what might have been 

 expected according to theory, more than the g\th of a cubic inch ; 

 nor was the difference greater in another instance, in which 2 

 cubic inches of carbonic acid gas were condensed by ammonia 

 in excess. 



As a farther test of accuracy, I may mention, that the salt 

 formed was exposed to the action of muriatic acid gas, and that, 

 as might be expected, this gas, in decomposing the carbonate, 

 disengaged exactly half its own volume of carbonic acid gas ; 

 I say exactly, for when l^th cubic inch was used, the gas evolved 

 from the salt in excess was, as near as possible, one-half, after 

 making allowance for a certain impurity in the muriatic acid gas 

 employed^. 



The tubes for transference were similarlj graduated and narrower. They 

 were cleaned by washing them, first with dilute muriatic acid, and afterwards 

 with distilled water ; and they were dried by means of fine warm cambric. 



• The trough had a cylindrical cistern attached to its bottom, to receive 

 the tube in which the gases were mixed, so that no calculation was required 

 for the effect of diminished pressure. 



•f- The carbonic acid was obtained from Carrara marble, by means of dilute 

 muriatic acid. Its degree of purity was ascertained, by introducing into it a 

 fillet of paper moistened with two or three drops of a strong solution of po- 

 tash over mercury, in a tube of the capacity of J cubic inch, divided into 50 

 parts. The ammoniacal gas obtained from salammoniac by quicklime, was 

 tried in the same way, by a fillet moistened with water. 



$ The muriatic acid gas was tested in the same manner as the ammoniacal 

 gas, and just before the experiment. This, I hardly need mention, is neces- 

 sary, as it is pretty rapidly decomposed when kept over mercury. 



