76 MOLECULAR WEIGHT AND POLYMERISM 



and 0-551 of the normal value 50 for iodine and thiophene. 

 They were found : 



In 100 gm. (p) Depression (#) MoL lowering M 



Iodine (M = 254) . . 0-914 0-129 36 \ 



. . 2-24 0-313 35 | instead of 32 



,, . . 4-27 0-601 36 \ 



Thiophene (if =84) . 0-51 0-192 31' 



. 1. 12 0-422 31 



. 2-16 0-812 3r instead of 28 



9i - 3-25 1-213 



A similar confirmation is supplied by Brunni's 1 experi- 

 ments on iodoform dissolved in bromoform. Here again 

 bromoform crystallized out with the dissolved body, and 

 the constant ratio (0-35 to 0-37) allowed of the conclusion 

 that solid iodoform consists of HCI 3 , as in liquid solution. 

 The molecular depression was found as 066 of the normal 

 amount, while 0-65 to 0-63 was to be expected. 



Isomorphous mixtures. Against this result, in all 

 respects satisfactory, has to be set the fact, observed 

 especially by Kiister l , that isomorphous mixtures sometimes 

 behave quite differently as regards melting point, which 

 may be calculated from the simple rule of mixture 



8 = 0,8! + (i -a) S 



where $ x , S 2 are the melting points of the components, and 

 a, i a the quantities (in molecules) of the two respectively. 

 Thus for hexachlor- and pentachlorbrom-ketopentane the 

 following results were found : 



Molecules Melting point Melting point 



C & Cl 6 0(a) C 5 a 6 rO(i-a) (o&s.) (caZc.) 



i o 87.5 (S x ) 



0-9471 0-0529 87.99 88-04 



0-9135 0-0865 88-3 88-38 



0.8571 0-1429 888 88-96 



0-8253 01747 89.11 89-28 



0-7468 0-2532 89-85 90-09 



1 Atti R. Accad. del Lincei (5) 7. 166. 



2 Zeitschr.f. Phys. Chem. 5. 60 1, 8. 577. 



