94 PROCEEDINGS OF THE AMERICAN ACADEMY 



It will be remembered that the mean value from five determinations 

 of the specific gravity of the hexagonal modification was 4.848. 



We made two analyses of the monoclinic iodide, each with a differ- 

 ent preparation, and the iodine was determined as described in our 

 previous paper. The small amount of impurity which would not dis- 

 solve in the tartaric acid solution was estimated in the first analysis, 

 but not in the second, and we therefore give in each case the per cent 

 of iodine in the crystals as they were weighed. 



Analyses of Monoclinic Antimonious Iodide. 



No Weight taken. ^^Sfiljarned.^' ^ % «f Io*ii"e- 



1. 1.3087 1.8332 75.73 



2. 1.8988 2.6605 75.70 



Mean value ; . . . 75.715 



Theory when Sb= 120 and 1 = 127 . . . 76.047 



The insoluble residue in the material of the first analysis weighed 

 two and one-half milligrammes ; and, were allowance made for this 

 impurity, the corresponding percentage of iodine would be raised to 

 75.87. We found, however, that this material, like the hexagonal 

 modification when crystallized from the same solvent, contained a 

 trace of oxi-iodide of antimony, which of course must also be taken 

 into the account before we can expect a close agreement with theory. 

 So far as our analyses indicate, the total amount of impurity in the 

 monoclinic crystals is not greater than that wliich we often find in the 

 hexagonal crystals when crystallized, like the first, from a solution in 

 carbonic disulphide. The difference seems to depend on the condition 

 in which the impurity is present : and the conception we have formed is, 

 that in the first case the impurity is a mere admixture like dirt en- 

 tangled by the crystalline structure, while in the last case it actually 

 adheres to the molecules. This molecular adhesion is induced by the 

 action of the light ; and our theory assumes, that, while the primitive 

 molecules thus loaded are prevented from macling, so as to produce 

 the triads of the hexagonal structure as shown in Fig. 1, so, also, 

 these loaded molecules, when united in the normal way as shown in 

 Fig. 2, form a crystal differing essentially, although still not very 

 widely, from the now familiar orthorhombic prism of sixty and one 

 hundred and twenty degrees. 



