WATER IN MURIATIC A^ID GA$. 26J9 



communication with the atmosphere, and which, it will be 

 shewn, is derived from the salt, and not from the air. 



Mr. J. Davy farther contrasts the small quantity of water 

 obtained from the muriate of ammonia in his brother's experi- 

 ment with the quantity which, according to the common doc- 

 trine, it contains ; this latter quantity, he seems to imagine, ' 

 ought to be procured j and, since it is not, he concludes that 

 that doctrine cannot be maintained. 



Any discussion with regard to the quantity of water obtained This kind of 

 by heating the salt in a close vessel, is probably superfluous. cu i^tedto C *" 

 That kind of experiment I never considered as one calculated showthequag^ 

 to afford a proper indication of the real quantity which the ^ 4 

 salt yields. I repeated it merely because Messrs. Davys affirm- 

 ed, that there is no appearance of water whatever. That as- 

 sertion is now proved to be incorrect, which is all that the repe- 

 tition of the experiment was designed to establish, and the 

 original mode of conducting it I consider as the one which 

 gives the true result. 



It may be remarked, however, to obviate any difficulty from Elucidation 

 this point, even with regard to the quantity obtained in the £ ron ] vari °»** 

 more favourable mode of conducting the experiment, that the 

 combination of muriatic acid gas with ammonia, was not re- 

 garded as adapted to determine the proportion of combined 

 water in the acid gas ; for, of all the combinations of this acid, 

 it is the one in which there is the greatest difficulty in separating 

 the water. Acids, in combining with salifiable bases, retain 

 the whole, or the greater part of their combined water, espe- 

 cially when these bases have also an attraction to water. To 

 expel this from the compound salt to any extent, a heat, equal 

 or superior to ignition, is in general required j and, by the most 

 intense heat, it does not appear, that the whole quantity is 

 expelled. Berthollet has shown, that after exposure to the 

 violent heat of a forge, salts retain water, so that when again 

 exposed to heat in mixture with iron filings, they afford hydro- 

 gen gas ; and this is the case even with those which appear to 

 have little attraction to water, as sulphate of barytes. Where 

 the salt, therefore, is volatile, such as muriate of ammonia, 

 the expulsion of its water must be imperfectly attained. The 

 degree to which the heat may be raised is not great, and, in 

 raising it, it must operate nearly with as much force on the real 



•alt, 



