372 M. De la Provostaye on the Isomorphism 



&c. &c. Acetic acid does not decompose it. Formula Cd S, 

 or C' H'- As-, S. Specific gravity of vapour 7*72, calculated 

 8-39. 



Protoseleniuret of cacodyl, C* H'^ As'-, Se, or Cd Se : pure 

 chloride of cacodyl is distilled several times with a solu- 

 tion of seleniuret of sodium : it is a transparent yellowish 

 fluid of very unpleasant smell ; insoluble in water, soluble in 

 fether and alcohol ; absorbs oxygen and deposits colourless 

 crystals : burns in the air with a blue flame. Nitrate of silver 



gives with Cd Se, Ag Se + Cd O, N. Corrosive sublimate 

 gives first black seleniuret of mercurj', and then a white pre- 

 cipitate, viz. hydrargochloride of cacodyloxide. This com- 

 pound is soluble in hot water, and crystallizes from it on 

 cooling. 



Protocyanide of cacodyl, Cd Cy, is formed by distilling 



concentrated hydrocyanic acid with alkarsin, or better by 

 treating a strong solution of bicyanide of mercury with alkar- 

 sin. By distillation an oily fluid collects under the water, 

 and on cooling forms large beautiful prismatic crystals; these 

 crystals are then distilled over baryta, &c. &c. Melts at 32° C; 

 boils at about 140° C; burns in the air with a reddish-blue 

 flame. Soluble in asther and alcohol, but little in water. It 

 is the most poisonous of all the cacodyl compounds, and one 

 must be excessively careful in experimenting with it. A so- 

 lution of silver gives cyanide of silver with Cd Cy. The ni- 

 trate of the dioxide of mercury is reduced by it, not so the 

 nitrate of the oxide. Sublimate gives the hydrargochloride 

 of cacodyloxide, &c. &c. Formula C* H'- As-, N- C-; spe- 

 cific gravity of the vapour 4-63, calculated, 4-547. The spe- 

 cific gravity of the vapour of cacodyl, C* H'- As', must 

 therefore be 7'281. We must reserve the conclusion of this 

 paper ibr our next. 



LXI. On theIso7noi-phismofOxamethane andChloroxamethanc. 

 By M. F. DE LA Provostaye, Professor to the Faculty of 

 Hennes*. 



A MONGST the numerous and important researches to 

 ■^-^ which the theory of substitutions has already given birth, 

 those of M. Malaguti upon chloroxalic astherf are without 

 doubt some of the most remarkable. We here see two com- 

 plete series of products, all derived from each other without 

 destruction, and by simple combinations or transformations ; 



* From the Annates de Cfiimie el de Plit/sique, vol. Ixv. p. 3s22. 



f An Abstract of this paper will appear in our next Number,— Edit, 



