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which thefe falts had fo entirely prevented putrefadion in the 

 flciii to which they Vv^cre united. Animal fubftances afford much 

 volatile all<ali, and now they are known to contain alfo a volatile 

 acid gas. While thefe two volatile principles continue united 

 with each other, they may prevent any material change from 

 taking place in the fubftancc; but if one of them by any means 

 efcapcs, the other will follow; the acid feems to be the mcft 

 volatile, and efcapcs firfl, though we may not be fenfible of its 

 efcape, becaufe it has no fuch ftrong fmell as the alkali has. 

 The letting loofe thefe volatile principles feems to be the begin- 

 ning of putrefaction. If this be the cafe, we may fee the 

 reafon why flefli, growing putrid, is reftored to fweetnefs by fixed 

 air, that acid replacing -what had efcaped, and retaining the volatile 

 alkali. It is probably on this account that the aerial acid is 

 found to be of ufe in flopping the progrefs of fome putrid dif- 

 cafes ; it feems to ad: as a fort of pickle. If vinegar preferves 

 flefh by keeping its volatile alkali united with this acid which 

 is not volatile, we may exped a fixed alkali will have a like 

 effed in preferving flefh, by expelling the weaker volatile alkali, 

 and uniting itfelf to the volatile acid, which will therefore be 

 retained. This I found to be really the cafe ; for, while the flcfh 

 and alkali were combining in the mortar, a very ftrong fmell 

 arofe like that of Jal volatile ; and at one time that I ufed a 

 brafs or metal mortar, I perceived its edges to be tinged with 

 blue, which fhewed the metal had been affeded by a volatile 

 alkali. 



S s 2 Thers 



