CiiA?. II.] Chemical PhilosopJnj. 121 



cularly the introduction of muriate of lime, m liicii 

 produces a very .2:reat degree of cold \\\\e\\ mixed 

 with snow. The e::periments of Lowitz have been 

 lately repe-ited and extended by Mr. Walker. By 

 means of tiie above-mentioned mixture, Mr. W. 

 H. Pep3^s, junior, of the London Philosophical So- 

 ciety, with the assistance of some friends, froze, 

 on the eighth of February, 1799, fifty-six ^:)onnds 

 avoirdupois of mercury into a solid mass. In this 

 process, the mercury in Fahrenheit's thermometer 

 sunk 6^i deg. below — a degree of cold ne\ er be- 

 fore produced in Great Britain. 



The inquiries of modern chemists into the nature 

 and properties of Ligiil have been scarcely less 

 numerous and interesting. Those discoveoes re- 

 specting this substance which fall under the science 

 of optics, have been mentioned in another place. 

 The capacity of other bodies to receive light, to 

 retain it in a fixed state, and after^vards• to part 

 with it, without alteration, was discovered by the 

 experiments of father Beccaria, Mr. Canton, Mr. 

 Wilson, and M. de Grosser. The affinity between 

 light and heat, and the similarity of their eiTects, 

 in certain cases, have been diligently investigated 

 by Dr. Franklin, Mr. Wedgewood, Messrs. Pictet, 

 Chaptal, and Dorthes, and especially by count 

 Kumford ami Di\ Herschel. The rt searches of M. 

 Berthollet and of Dr. Bancroft, in the philosophy 

 oi permanent colours, upon chemical principles^ 

 wxrc mentioned in the preceding chapter. The (ex- 

 periments of Dr. Priestley, the abbe Tcssier, Dr. 

 Ingenhouz, and others, on the effects of light upon 

 growing vegetables, and the curious inquiries of 

 TJerschel, into the ditferent heating and illuminating 



