286 ©N THE OPTICAL PROPERTIES 



It is highly desirable, therefore, that the Chemical Philoso^ 

 pher would avail himself more frequently of the agencies of 

 light ill the prosecution of his inquiries. The various products 

 to which his attention is constantly directed, cannot always be 

 preserved for subsequent examination, and can seldom be pro- 

 cured by the Experimental Philosopher. An opportunity is 

 thus lost of confirming his own results, and of contributing 

 most essentially to the progress of optical knowledge. It is by- 

 the alliance, indeed, of Chemistry with Optics, that great revo- 

 lutions are yet to be effected in Physics ; and the time is pro- 

 bably not very distant, when, by their united efforts, we shall 

 be able to develope those mysterious relations among the ele^ 

 mentary principles of matter which hypothesis has scarcely 

 ventured to anticipate. 



In the following paper, I propose to describe the opticaT 

 properties of Sulphuret of Carbon, Carbonate of Barytes, and 

 Nitrate of Potash, and to illustrate the conclusions to which, 

 some of these properties lead, respecting the structure of dou- 

 bly refracting Crystals. 



I. Sulphuret op Carbon; 



This remarkable fluid was lately discovered by Lampadius. 

 It is pure and colourless like water ; has a specific gravity of 

 1.272; is remarkable for its extreme volatility ; and is compo- 

 sed of 85 parts of sulphur, and 15 of carbon. 



Owing to the great length of spectrum which this substance 

 produces, I found considerable difficulty in measuring the 

 mean index of refraction. By taking the bisecting ray beyond 

 the green rays, and very considerably advanced upon the blue- 

 space, I obtained the following results : 

 ,/ O -i- -l^^ Angle- 



