Proceedings of Phihsophkal Societies, [May, 



a memoir of which we have given an account, having subjected 

 different gases to the same operation, obtained similar effects. 

 Hence it was concluded, apparently with reason, that the same 

 effects ought to appear with all the aeriform fluids. But M. de 

 Saissy, a physician in Lyons, having repeated the experiments 

 of M. Dessaignes, could only produce light with oxygen gas, 

 muriatic acid gas, and common air. Oxygen gas gives the 

 most light, muriatic acid gas comes next' in order, and common 

 air gives the least of the three. The other gases do not become 

 lominous, except when some oxygen is mixed with them. M, 

 de Saissy concludes from this that the aeriform fluids have not 

 the property of giving out light by compression, except when 

 they contain oxygen free, or feebly combined. He thinks that 

 this fact, when once well established, will give additional pro- 

 bability to the opinion that heat and light are different sub- 

 stances. 



The doctrine of M. le Comte Berthollet on the different 

 actions which influence the definite results of chemical pheno- 

 mena, depends in a great measure upon this almost general fact, 

 that an aikali which decomposes a saline compound only de- 

 prives it of that portion of its acid to which it owed its solubility, 

 and as soon as it becomes insoluble it precipitates, preserving 

 the re^t of its acid, and frequently taking with it even a portion 

 of the alkali which acted on it ; so that the precipitate is almost 

 always a compound. Yet M. Taboalda had announced that the 

 pure alkalies throw down from corrosive sublimate an oxide of 

 mercury free from all acid. M. Berthollet repeated this experi- 

 ment, and found that the precipitate is not pure unless more 

 alkali be added to the solution of corrosive sublimate than is 

 necessary to saturate all the muriatic acid present. When this 

 is not added the precipitate always retains a portion of acid, 

 v./bieli varies according to circumstances. The kind of alkali is 

 indifferent. But when the potash, for example, is completely 

 saturated vv'ith carbonic acid, it does not decompose the corrosive 

 sublimate If we employ a subcarbonate, it acts till it has lost 

 its redundant potash 3 but the precipitate contains both muriatic 

 ^cid and potash. 



The alkalies produce the same effects on the nitrate of the 

 peroxide of mercury, and experiments made on the sulphate of 

 alumioa gave analogous results; that is to say, they confirm the 

 iaw established by M. Berthollet. 



The same philosoplier had made experiments long ago to 

 determine the proportion of oxygen and muriatic acid which 

 constitute oxymuriatie acid 5 but Mr. Chenevix having obtained 

 dliierent results, M. Berthollet returned again to the same sub^ 

 je€t, He found that the light which he had at first ejnployed as 



