1S58 Dr Davy on the Comhinations of 



no cooling means employed, reaches the neck of the retort, and 

 even passes into the receiver : next, a salt which appears to be 

 a mixture of the preceding, and of the sesquicarbonate ; and 

 lastly, the same mixture with a great excess of water. 



Of these saline products, none that I have examined by the 

 methods of analysis described, have contained more ammonia 

 than the carbonate. The salt which is most volatile, and conse- 

 quently passes farthest before it condenses, contains about the 

 same proportion of ammonia as the anhydrous carbonate, and 

 appears to differ from it only in containing water, — in fact, in 

 being a hydrated carbonate. Dr Thomson, in the last edition 

 of his System of Chemistry, states, that " the carbonate may 

 be formed by mixing one volume of carbonic acid gas, two vo- 

 lumes of ammoniacal, and one volume of the vapour of water */' 

 I have thus obtained it over mercury ; and it has exhibited the 

 same properties as that which my brother first procured by dis- 

 tillation, especially the property of deliquescing on exposure to 

 the atmosphere, of which no mention is made by Dr Thomson, 

 or by any other chemical writer that I have had it in my power 

 to consult. 



Relative to the statement of my brother, contained in his re- 

 searches already referred to, that the proportion of alkali capa- 

 ble of combining with carbonic acid may vary between 20 and 

 SO per cent., according to the temperature at which the combi- 

 nation is made ; I believe he was deceived by the methods of 

 analysis which he employed, as none of the trials which I have 

 made have confirmed his conclusion. I shall mention the results 

 of one experiment only, in which the carbonate of ammonia 

 carefully made with dry gases, over dry mercury, was exposed 

 to a temperature of about 170°, gradually raised, through the me- 

 dium of a mercurial bath. As long as the temperature was below 

 140°, the salt appeared unaltered, no gas was disengaged ; 

 proving that there was no change of composition. When the 

 temperature was raised to 140°, the salt presently became ga- 

 seous, and, as well as I could judge, occupied just the same space 

 as its ingredients did before combination. When reduced below 

 140°, the gaseous salt, whether in the upper part of the jar, or 



* System of Chemistry, ii. p. 384, — 7th edition. 



