of the Cacodyl Series. 38 S 



solution, which is at first clear, becomes of a dark colour on 

 further solution of the metal. Water separates the pure chlo- 

 ride of tin, and leaves cacodyl mixed with a trace of chloride 

 of cacodyl behind : — 



KdCll _ /Kd 

 Sn J -\Sn CI. 



As zinc, however, effects the reduction of the chloride with 

 the greatest facility, and as no further decomposition takes 

 place in the chloride of zinc formed, I have in my experi- 

 ments exclusively used this metal for the isolation of the 

 radical. 



Notwithstanding that the reduction appears so easy, still, 

 as it is very difficult to prevent subsequent decomposition in 

 repeating the distillation and crystallisation of a substance 

 which is as inflammable as the vapour of phosphorus, I think 

 it necessary to enter into further details regarding the method 

 of producing it. 



Very thin sheet zinc, the surface of which has been pre- 

 viously cleaned with dilute sulphuric acid and afterwards well 

 washed, is cut into small pieces, to be employed for this pur- 

 pose. The chloride of cacodyl must be quite free from oxy- 

 gen. By digesting oxide of cacodyl three times over in con- 

 centrated hydrochloric acid, a pure substance is procured, 

 which does not give off any vapour. This chloride must be 

 allowed to remain in a close vessel with chloride of calcium 

 and caustic potash, without being distilled, in order to deprive 

 it of any water it may contain, and also of any excess of acid. 

 To prevent all access of air in this operation, a glass vessel 

 of this description is employed (fig. 1.). At 

 the opening o, a stream of carbonic acid is con- '^' ' 



ducted through the vessel with the bulb c, to 

 contain the substance to be dried. When the 

 atmospheric air is entirely displaced, both ends, 

 a and b, are sealed. When the vessel is re- 

 quired for use, the point a is broken and at- 

 tached by a caoutchouc tube connected to an 

 air-pump; the point b is then broken and put 

 under the surface of the chloride of cacodyl ; the 

 latter is sucked up into the apparatus, and then 

 immediately closed : I will call this the drying 

 apparatus. The reduction and distillation is 

 carried on, in a somewhat similar manner, in an 

 atmosphere of carbonic acid, in a closed vessel 

 (fig. 2.), the bulb a being the distillation tube, and the bulb 

 b the receiver. 



The whole apparatus being previously filled with carbonic 



