Mr. T. E. Thorpe on the Specific Volumes of Liquids. 555 



an element is invariable when in combination. Exceptions to the 

 law occur, however, in the cases of oxygen and sulphur, each of 

 which bodies has two specific volumes dependent upon the manner 

 in which they are held in union. When contained " within the 

 radicle," as in acetyl, C 2 H 3 0, oxygen has the value 12*2, but when 

 existing " without the radicle," as in alcohol, it has the smaller value, 

 7*8. Sulphur, when " within the radicle," has the specific volume 

 28-6 ; when " without the radicle," it has the specific volume 22-6. 



The cause of these variations may be thus stated in the language 

 of modern theoiy : — When dyad sulphur and oxygen are united to 

 an element by both their affinities, their specific volumes become 

 respectively 28*6 and 12-2 ; when they are attached by only one 

 combining unit, their specific volumes are 22-6 and 7*8. 



Phosphorus is regarded by certain chemists as invariably a triad ; 

 others maintain that it is sometimes a triad, at other times a pentad. 

 In the trichloride it is a triad, in the oxychloride and thiochloride 

 it is a pentad. According to this view, the two latter compounds 

 possess the following constitution : — 



CI CI 



C1_P=0 C1-P=S 



If, however, phosphorus is invariably trivalent, the oxychloride and 

 thiochloride must possess the formulae 



O CI 



P-O-Cl P-S-Cl 



I I 



CI CI 



It is possible to decide between the two modes of representing 

 the constitution of these compounds, if it be granted that the varia- 

 tion in the specific volume of oxygen and sulphur is due to the 

 manner in which these elements are held in union. Eor, if the 

 phosphorus in the oxychloride and thiochloride be quinquivalent, 

 the oxygen and sulphur must possess the greater of the two values, 

 since both their combining units are united to the phosphorus ; 

 if, on the other hand, phosphorus be trivalent, the oxygen and 

 sulphur must possess the smaller of the two values. 



The author has determined the specific gravity, boiling-point, and 

 rate of expansion of P Cl 3 , P O Cl 3 , and P 8 Cl 3 , in order to ascer- 

 tain the specific volume of the oxygen and sulphur in the two latter 

 compounds, and consequently the chemical value of the phos- 

 phorus ; and he finds that the specific volumes of the oxygen and 

 sulphur are almost identical with the values given by K opp for 

 these elements when " without the radicle." It would therefore 

 appear that the oxychloride and thiochloride must possess the 



