GAY-LUSSAC 183 



celebrated Madame de Genlis, and her teaching was 

 planned on the principles of Rousseau. 



In addition to his discoveries and researches in 

 chemistry, Gay-Lussac was a brilliant physicist. The 

 law of the expansion of gases was discovered by him 

 and Charles : a gas expands -g^-g^d f its volume for each 

 degree of temperature (Centigrade) above C ; or, in other 

 words, the law of Gay-Lussac states that all gases in 

 all conditions present one coefficient of expansion 

 Q'00367 ; that is, when heated from to 100 they 

 expand like air, namely, a thousand volumes of a gas 

 measured at will occupy 1367 volumes at 100. 

 Eegnault, in the year that Gay-Lussac died (1850), 

 showed that Gay-Lussac's law is not entirely correct. 



Gay-Lussac invented an alcoholmeter. It is used to 

 determine the strength of spirituous liquors ; that is, 

 the proportion of pure alcohol which they contain. He 

 also invented the syphon barometer. In this barometer 

 both the longer and shorter limbs are closed, but the 

 shorter one contains a capillary aperture through which 

 the atmospheric pressure is transmitted. 



Gay-Lussac invented an apparatus for ascertaining 

 vapour densities. It involved the determination of the 

 volume of a given weight of vapour ; but this method 

 and those of Dumas, Bunsen, and Hofmann have been 

 superseded by that of Victor Meyer, or the air-displace- 

 ment method. 



