CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 CASE SCHOOL OF APPLIED SCIENCE. — XLIV. 



A METHOD FOR DETERMINING THE INDEX OF RE- 

 FRACTION OF SOLID HYDROCARBONS WITH THE 

 PULFRICH REFRACTOMETER. 



INDEX OF REFRACTION OF THE SOLID HYDROCARBONS IN 



PETROLEUM* 



By Charles F. Mabery and Lee Shepuerd. 



Accepted June 6, 1902. 



One of the most important physical constants of liquids is the index 

 of refraction from which the molecular refraction may be calculated. 

 Of the two forms of apparatus in use for these determinations, the 

 Abbe and Pulfrich refractometers, the latter is in all respects the most 

 convenient. But neither refractometer as constructed permits of the 

 determination of the index of solid bodies, which requires a rise in 

 temperature sufficient to liquify the solid. So far as we are aware no 

 method has been proposed for determining the index of solids. The 

 only method suggested for ascertaining the index of liquids at increased 

 temperatures is that of Briihl (Ber. d. deutsch. Chem. Gesellsch. 24, 

 286, 1891), which depends on raising the temperature to the desired 

 point by means of a copper bar of peculiar shape, extending to a suf- 

 ficient distance from the prism to be heated by a lamp. Sufficient heat 

 is applied to the bar to reach the desired temperature over the prism by 

 conduction. A stirer is also attached to insure equal heating of the 

 li(juid. 



But this method is not satisfactory, especially for solids, since they 

 require temperatures for melting that are difficult to maintain constant 

 by external application without breaking the joint between the prism 

 and the glass cup which holds the liquid. It occurred to us that a more 

 convenient source of heat for melting solids miglit be supplied by means 



* The soUd hydrocarbons used in the preparation of tliis paper were prepared 

 in tlie work carried on with aid granted by the Academy from tlie C. M. Warren 

 Fund for Chemical Research. 



