1919.] Interaction of phosphorus halides. 265 
Both the brownish black and reddish brown arsenic ob- 
preparation of pure colloidal arsenic by this method is in view 
and may be of physiological importance 
he reaction seems to take pate eb to the following 
ane :—As,0, + 3PCl,+9H,O = 2As+3H,PO, + 9HCI. 
osphoric acid has been Paet in ‘the’ filtrate. It 
appears that the reaction proceeds to completion if excess of 
phosphorus tri-chloride be maintained in the system an 
actual experiment 59°1% of the arsenic content of the solution 
was precipitated by a single addition of phosphorus tri-chloride 
and the filtrate on treatment with more phosphorus tri-chloride 
gave a further precipitation of metallic arsenic. With phos- 
of the iodide, is responsible for the reaction. The nature of 
this intermediate compound cannot be established without 
phosphorus acid reduces the arsenic compound: or in other 
words phosphorus acid at the moment of its formation is in a 
more reactive state. If this view proves to be true, this behavi- 
our of a ae molecule may be likened to the nascent 
state of an elem 
In poedacerrr herewith reference may be made to a paper 
by R. G. Durrant on the interaction of stannous chloride and 
arsenious chloride (Trans. Chem. Soc., 1919, 115 & 116, 134) 
which was first noticed by A. Bettendorf (Sitzungsber. Neider- 
rhein. ar Bonn, 1869, 128). The arsenic arg ed by the 
authors by reduction with stannous chloride is buff — 
and soluble in carbon disulphide and never ies from tin. 
This evidently differs from the arsenic as precipitated above 
with phosphorous halides. 
My peat thanks are due to Prof. Sir. P. C. Ray for his 
kind ~staine ay eamial and advice. 
ee Se ee 
