KKFKACTIVK INDICES OF THE ELEMENTS. 



337 



TABLE VI. Refractive Index of Phosphorus. Preliminary Experiments. 



In the next series of experiments greater precautions were taken. The phosphorus 

 used was freshly prepared, and was free from discoloration. About a quarter of a 

 gramme was cut from the stick under water, rapidly dried on blotting paper in a 

 current of dry CO,,, and placed in a glass tube which ended in an open capillary. 

 Here it was further dried in a current of CO S for about a quarter of an hour, 

 when the tube was exhausted and sealed off. The phosphorus was then melted 

 in racuo and freed from impurities by being run into the capillary part of the tube, 

 where a convenient portion, isolated by judicious warming, was sealed off in a length 

 of atxmt 1 centim. The whole operation was conducted in a dark room with the 

 least possible light, and the phosphorus appeared quite clean and transparent. The 

 refractometer tube, after being dried, was filled with CO 4 , and the capillary was 

 scratched with a glass knife, weighed, and broken in a current of CO* Both halves 

 were instantly dropped into the refractometer tube, and this was immediately 

 exhausted and sealed off. After the experiment, the two halves of the capillary were 

 re-weighed, and the weight of phosphorus used calculated by subtraction. The 

 condition of the phosphorus alter each experiment afforded a trustworthy test of its 

 success. If a leak occurred, the phosphorus was found on the sides of the tube in 

 red scales. But if all had gone well, it was seen to be condensed into a colourless 

 transparent bead in one part of the tube. No experiment in which this was not 

 the case was accepted. With these precautions, remarkably constant results were 

 obtained. 



VOL. CC1V. A. 2 X 



