182 ON THE NEW SYSTEM OF CHEMISTRY. 



His experiments After repeating my experiment, which he found to be jufi, 

 oxides and char- Mr. Cruikihank did the fame with the calces of other metals, 

 coal, in proof, particularly thofe of zinc, copper, lead, and manganefe, and 

 then concludes, p. 4, that in all thefe cafes u the air muft 

 M come from the partial decompofition of the carbonic acid by 

 are inferred by « the calx when raifed to a high temperature." But the in- 

 that the oxides ference that I think is more naturally drawn from them is, that 

 contain water, all thefe calces contain much water, and little or nothing elfe. 

 This I have fhewn to be the cafe with refpecl to feveral of 

 them, efpecially that of zinc ; though I doubt not but that 

 fome fmall portion of oxigen may be contained in them all. 

 Indeed, we cannot abfolutely fay, that any fubftance what- 

 ever can be wholly expelled from any other, with which it 

 has been chemically combined by any procefs. 

 Jron or its oxide Before Mr. Crurkthank admitted that iron, or its calx, 

 fohrVocus in wnen raifed to a high temperature, can decompofe carbonic 

 carbonic acid is acid (i. e. fixed air) in this experiment, he mould have tried 



^rotic^no dc- whether "* would do ifc in an y other - If in a "y Cafe, I fliould 

 compofitionj think it would do it when it was heated in this air by a burn- 

 ing lens, by which a greater heat may be produced than in 

 any open fire. But this I found not to be the cafe either with 

 iron, or this calx of it. In the laft fummer I went through a 

 courfe of experiments with this view ; but I always found 

 for though part fixed air not to be decompofed by this means. Though I 



immifdWewith **° UncI that a P ortion of tnis air > and alfo of a11 tne other kinds 

 ■water by thus that are readily imbibed by water, was rendered immifcible in 

 heating either an wa t er by means of heat reflected either from a calx of any 



oxide or a piece J . ■ , . irin 



of earthen cru- metal, a piece ot earthen crucible, or any other iubltance, on 

 able in it j which I threw the focus of the lens when it was furrounded 

 yet there was no by this kind of air confined by mercury or water : This, 

 addition of oxi- however, was no decompofition of the air, as there was no 



gen, but only r 



azote. oxigen found in it after the procefs. The addition of perma- 



ment air was always phlogifticated, 



Mr. C. pro- Mr, Cruikfhank thought, that if this heavy inflammable 



duccd heavy in- a i r came from the decompofition of the carbonic acid by the 



fromfron lungs iron, he fliould fucceed better, p. 4. by employing iron filings 



and chalk heated }i n the place of finery cinder, as they would have a greater 



affinity with oxigen ; and with this view he heated them tor 



gether a quantity of common chalk, previoufly expofed to a 



low heat, for ten minutes. From this mixture he procured a 



great quantity of air, and he thought that the acid {i. e, fixed 



ajr 



