The Molecular Volume of Solids. 



463 



of the oxides, oxygen has three distinct volumes, 16, 32, and 64 (his 

 numbers are adapted to the atomic weight of oxygen = 100), which 

 are in the simple numerical proportion 1, 2, and 4, but he never 

 extends this principle to the other elements, unless it be, perhaps, to 

 chlorine and the lighter metals ; for, in the chlorides, the two values 

 which he assigns to chlorine, 196 and 245, are in the ratio of 4:5; 

 but then it is necessary to assnme new volumes for the metals, which, 

 like potassium, sodium, calcium, and magnesium, nndergo condensa- 

 tion in the act of combining ; and the volumes thus assumed for them, 

 exhibit no simple relation to the metals in an uncombined state. To the 

 acid radicle S0 4 in the sulphates two volumes are likewise assigned, 

 186 and 236, which bear no simple relation to each other, and are not 

 derived from the constituents of the radicle. To the radicles Cr0 4 , 

 C0 3 , and N0 3 , in the chromates, carbonates, and nitrates, are assigned 

 the volumes 228, 151, and 179, but then it does not appear that any 

 connexion is traced between these nnmbers and the components of the 

 respective radicles. 



Schroder propounds the following principle : — " In every solid 

 compound the volume measnre (volume-maas) or the stere, of one 

 of its elements, which, through the forces acting during crystallisation, 

 determines all the other components and respective constituents, 

 causes equal volume measures to take up equal steres. In other 

 words, one of the elements assimilates all the others." 



The number of atoms of each element in a compound is indicated 

 in the ordinary manner by a whole number placed to the right of the 

 nnder side of the symbol, and the number of its steres by a whole 

 number to the right of the upper side. The stere is distinguished by 

 an overstroke, and the observed and calculated volumes by a similar 

 understroke. The element in a compound which determines the stere 

 is also indicated by an overstroke; thus metallic silver is Agl=2x 

 5-14=10-28, observed volume= 10-28. Again, the chloride, bromide, 

 and iodide of silver are represented thus : — 



AjjOi;=5x 504= 2570 obs. vol. =2570. 

 AgBrt=6x5 T l4= 30-81 „ =30-81. 

 Agl^=8x5 T 14= 41-12 „ = 41-12 . 



From this it is seen that in all these compounds the silver stere 

 dominates. 



Mercury has a stere = 5-52. Thus : — 



Mercurous oxide =Hg|Of= 1 x 5 T 52 = 3^64 obs. vol. 38-64. 

 Mercnric oxide=HgO£=7 x 5 7 52=38-64=2 x 19-38 obs. vol. 19-32. 



