of Sulphate of Carbon. 119 



elementary principles ; and whatever confidence we may place 

 in the skill of the chemist, or in the accuracy of his methods, the 

 mind can never rest satisfied with the results of an analysis which 

 is directly opposed by optical phsenomena. 



It is highly desirable, therei'ore, that the chemical philosopher 

 would avail himself more frequently of the agencies of light in 

 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 procured by the 

 experimental philosopher. An opportunity is thus lost of con- 

 firming his own results, and of contributing most essentially to 

 tlie progress of optical knowledge. It is by the alliance, indeed, 

 of chemistry with optics, that great revolutions are yet^to be ef- 

 fected in physics ; and the time is probably not very distant, 

 \vhen, by their united efforts, we shall be able to develop those 

 mysterious relations among the elementary principles of matter 

 which hypothesis has scarcely ventured to anticipate. 



In tlie following paper, I propose to descriije the optical pro- 

 perties of sulphuret of carbon, carbonate of barytes, and nitrate 

 of potash, and to illustrate the conclusions to which some of these 

 ))roperties lead, respecting the structure of doubly refracting 

 crystals. 



I. Sulphuret of Carhon. 



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 composed 

 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 : 



Angle of the prism 8"^ 10' 



Angle of refi-action 5° 38' 



Refractive power 1'6S7 



By considering the bisecting ray, as passing through the green 

 space, and near its confines with the blue, the following mea- 

 sures were ol)tained : 



Angle of the prism 8M0' 



Angle of refi-action 5" 27' 



Refractive power 1*6632 



As the sulphuret of carbon has nearly the same action upon the 

 red and green rays, as balsam of Tolu, I have no doubt but 

 that the bisecting ray is considerably advanced upon the blue 

 space, and that the mean index of refraction is nearly 1*680. 



H 4 A prism 



