1876.] Specific Volumes of Liquids. 289 



method of determining the expansion of liquids tends to give low 

 results *. 



The specific gravity of vanadyl trichloride at 127°*19 is 1-63067; 



hence its specific volume is TTaafu&f = 106*54. 



It is thus evident that the specific volumes of vanadyl and phosphoryl 

 trichlorides are not equal; the compound with the higher molecular 

 weight has the greater specific volume. 



In the communication on the chlorides of phosphorus already referred 

 to, it is shown that if we assume, as appears in the highest degree pro- 

 bable, that there is a relation between the manner in which the oxygen 

 atoms in a compound are held in union and their specific volume, it 

 follows that the oxygen atom in POCl 3 possesses the smaller of the two 

 values 12*2 and 7*8 assigned by Kopp to oxygen, and accordingly that 

 this atom is attached to the phosphorus by only one combining unit. 



Thus 



CI 



P_0— CI 



I 



CI, 



showing that the phosphorus atom in phosphoryl trichloride possesses 

 the same atomic value as in phosphorus trichloride. 



As the difference between the two values for the volume of oxygen, 

 viz. 12-2 — 7*8 = 4-4, is but little less than that between the specific 

 volumes of YOCl 3 and POCl 3 , viz. 106-54—101-58 = 4-96, it is possible 

 that the difference in the specific volumes of the two liquids may be due 

 to the different manner in which the oxygen atoms are united to the 

 vanadium and phosphorus atoms; for, if V be regarded as a pentad, 

 VOCl 3 must be written 



CI 



CI— v=o 



I 



CI, 

 the oxygen atom having the value 12-2. Assuming Kopp's value 

 for CI, viz. 22-8, this would leave for P and V nearly the same specific 

 volume, viz. 



P 25*4 



Y 25-9 



Prom the uncertainty respecting the particular volume to be assigned 

 to the oxygen atom in vanadyl trichloride, our knowledge of the specific 

 volumes of VOCl 3 and POCl 3 gives us little aid towards solving the 

 question whether the several members of a family of elements have 

 identical specific volumes. 



* Phil. Trans. 1866. t Y=5P35, Koscoe; 01=3546, Stas. 



