847 



obtained perfectly pure, having dissolved about one per cent, of the 

 products of decomposition, which are not removed by subsequent 

 crystallization. 



Potash and soda in the cold unite with the nitroprussides, and 

 form distinct salts, in which there is one equivalent of these alkalies 

 for every equivalent of the baryle. These alkalies when heated 

 with the nitroprussides decompose them altogether, forming peroxide 

 of iron, hyponitrites, oxalic acid and ordinary ferrocyanides. 



Sulphuretted hydrogen and soluble sulphurets also decompose the 

 nitroprussides. 



The formula of the nitroprussides is remarkably complex. Well- 

 accordant analyses of all the salts permit no simpler relation between 

 their carbon and iron than 24 equivs. of the former to 5 equivs. of 

 the latter. The simpler proportion of 25 to 5 or 5 to 1, cannot be 

 drawn legitimately from their composition. Analysis, and also a 

 study of their transformation, show that they contain nitrous oxide, 

 and have led to the complex formula 



Fe5Cyi23NO + 5R. 



This is obviously a conjugate formula, and allows itself to be divided, 

 for reasons now to be given, into the more simple expression 



SCFcsCysNO + 2R) + (FeCysNO + R). 



The relation of nitroprussides to ordinary prussides is supposed 

 to be as follows : — 



Both the ferrocyanides and the ferridcyanides are supposed to 

 contain a common radical, one being quadribasic and the other 

 tribasic, just as in the case of the modifications of phosphoric acid. 

 A bibasic modification is therefore to be looked for. The formulae 

 would be as follows : 



Ferrocyanides (Fe2Cy6) + 4R. 



Ferridcyanides (FcsCye) + 3R. 



Hypothetical compound .. (Fe2Cy6) + 2R. 



The nitroprussides are supposed to correspond to the last of the 

 series, in which one equivalent of cyanogen is replaced by one equiv. 

 of nitrous oxide. In the case of the beautiful purple compound 

 produced by the soluble sulphurets on nitroprussides, this nitrous 

 oxide is replaced by sulphuret of nitrogen. The hypothetical 

 bibasic prusside necessary to establish this view has not yet been ob- 

 tained ; but the author states that experiments made with this view 

 have already been so successful, that he shortly expects to announce 

 it to the Society. 



9. " On the Structure of the Dental Tissues of Marsupial Ani- 

 mals, and more especially of the Enamel." By John Tomes, Esq. 

 Communicated by Dr. Grant, F.R.S. 



The author of this communication, after examining microscopi- 

 cally the teeth of many marsupial animals taken from the majority of 

 the families that make up the order Marsupialia, finds that they possess 

 a structural character by which they may be distinguished from other 



