358 Professors W. B. and R. E. Rogers 



decomposing the chloride of calcium and liberating hydrochloric 

 acid. 



It is evident therefore that the application to Rose's apparatus 

 of a heat sufficient to expel the carbonic acid from the solution, is 

 entirely inadmissible, whichever solvent we employ. It is scarce- 

 ly necessary to add that this remark is also applicable to the ap- 

 paratus of Fritche, that of Will and Fresenius, and that of Erd- 

 man and Marchand. 



As in a recent memoir of the two chemists last named, they 

 express a preference for sulphuric acid in experiments of this kind, 

 it becomes important to our enquiries to ascertain whether the 

 sulphuric solution produced in such case, would retain enough 

 carbonic acid to make the boiling process necessary. We there- 

 fore introduced into the bottle one hundred grains of carbonate 

 of lime, and poured upon it a sufficient amount of sulphuric acid, 

 diluted with an equal bulk of water, to prevent the formation of 

 a thick magma. Notwithstanding the large excess of acid, and 

 frequent agitations of the liquid, the action towards its close was 

 extremely slow, so that at the end of four hours, a slight crepi- 

 tation could be heard on stirring the mixture. When this had 

 entirely ceased, the liquid was heated in the graduated tube as 

 above described. As the temperature approached boiling, car- 

 bonic acid was evolved, and at the close of the process, the vol- 

 ume of this gas collected was upwards of four tenths of a cubic 

 inch. A similar result was obtained with several other carbo- 

 nates and sulphuric acid. 



We are therefore justified in affirming, that the solution or mix- 

 ture formed in this process, whether sulphuric or hydrochloric 

 acid be used, always contains an amount of carbonic acid too 

 great to be overlooked in accurate research ; that this carbonic 

 acid cannot be expelled by a heat below boiling, and that such a 

 temperature cannot be applied to the liquid while in the appara- 

 tus, without entirely vitiating the result. We therefore attach 

 much importance, in cases of nice research, to the separate heat- 

 ing of the liquid, and we believe that with proper care the process 

 for that purpose above described, will give the amount of residu- 

 ary carbonic acid with all needful exactness. 



The critical nature of the researches in which we proposed to 

 employ the above mentioned instruments and processes, made it 

 necessary, before entering on the main objects of investigation, to 



