PHOSPHORUS, SULPHUR, AND SELENIUM. 



37 



datum with mercury alone in the jacket, was 0.079 (see table on p. 31). 

 Hence the equation becomes 



(0.696 0.079 0.2031 X 2.075)4.28 , 



ij _. O . i J- _x\ -L \J 



5428 X 19.48 

 or = 0.00000116 



The data and results concerning the substances under investigation are 

 recorded in the table below. 



Data concerning the compressibility of five non-metals. 



1 These two determinations were made by W. N. Stull; all the others by F. N. Brink. 



DISCUSSION OF RESULTS. 



The study of these results is interesting. It is to be noted in the first 

 place that, as was predicted, carbon and silicon have low compressibilities, 

 although the former of these substances gives a larger value than had 

 been anticipated. Silicon has the lowest compressibility, 0.16 X 10~ 6 , of 

 any of the substances included in this series of papers. 



In seeking for an answer to the question as to why the value for carbon 

 should not be still lower than it is, an obvious one suggests itself at once 

 in the different states of aggregation of the two substances. The silicon 

 was compact and crystalline, the carbon in a loose friable mass. That 

 carbon also is but little compressible when crystalline may be inferred 

 from the behavior of carborundum, which is but little more compressible 

 than silicon itself, although containing almost 30 per cent of carbon. 

 Assuming for the moment that compressibility is an approximately additive 

 property (an assumption which only holds true when, as in this case, no 

 great volume-change occurs in producing a compound from the two ele- 

 ments) it is easy to calculate from the compressibilities of silicon and 

 carborundum that the compressibility of crystallized carbon must be about 



