THE MOLECULAR VOLUMES OF LIQUIDS 197 



of organic compounds of sulphur also tends to elucidate their 

 probable structural formula, and, incidentally, the varying 

 valency of the sulphur atom. 



A large amount of work has been done upon the molecular 

 volumes of the different classes of nitrogen compounds, organic 

 and inorganic, and a number of significant regularities have 

 been detected which serve to throw light upon the structure 

 of their members. It would exceed the space at our disposal 

 to attempt to deal in detail with the mass of experimental 

 material which has been accumulated. This has been sifted 

 and discussed by Mr. Le Bas, and we must therefore refer the 

 reader who desires fuller information to his treatise. Many 

 illustrations might be given from the study of the nitrogen 

 compounds of the value of observations on molecular volume 

 in affording an insight into molecular arrangement and struc- 

 tural grouping. 



The same remark applies with equal force to the liquid 

 compounds of the other typical members of the trivalent series 

 — phosphorus, arsenic, and antimony. Phosphorus, as in the 

 case of certain other elements, would appear to have a much 

 smaller molecular volume when free than when combined, and 

 this fact is consistent with the statial arrangement of the 

 phosphorus molecule, which is known from other physical 

 considerations to be complex. The number of phosphorus 

 compounds which are available for determinations of molecular 

 volume is, of course, far less than in the case of nitrogen, as 

 many groups of nitrogenous compounds have no analogues 

 among the other members of the trivalent series. The greater 

 number of the phosphorus compounds which have been ex- 

 amined are inorganic. They are of comparatively simple 

 constitution, the results are consistent and offer little difficulty 

 in interpretation. 



As regards phosphorous oxide, Mr. Le Bas points out 

 that its molecular volume might easily be found experi- 

 mentally : apparently he is unaware that it was so found by 

 the present writer and Dr. Tutton as far back as 1890 {Journal 

 Chemical Society, 57 (1890) 559). The value thus obtained 

 agrees with that calculated on the assumption that the ring 

 grouping and consequent volume of the free phosphorus 

 molecule (P 4 ) is preserved in P 4 6 , which seems otherwise 

 probable^ and that the oxygen atoms are singly linked and 



