180 Prof. Bunsen on Kakodylic Acid, 
trast with the dark ground of the paper. Specimens of the 
spectrum itself are subjoined for inspection, 
216. The black positive paper used in the above experiment 
(which has been often repeated with the same results) con- 
tains free nitrate of silver. If this be washed out, the dark- 
ening at the lower end of the spectrum is not produced, but 
in its place the feeble subsequent bleaching in the region 
above-mentioned commences at once. And if besides washing 
with mere water, the paper be subsequently washed with a 
neutral hyposulphite to remove all chloride of silver, it is re- 
duced to a state of perfect insensibility. It is therefore to this 
latter element that the direct action of the bleaching rays is 
to be referred. A few months’ keeping also destroys the po- 
sitive sensibility of the paper in question entirely. 
Collingwood, June 13, 1842. J. F. W. HerscHet. 
[The Postscript of August 29 will follow in continuation. ] 
XXVIII. On Kakodylic Acid, and the Sulphurets of Kakodyle. 
By Professor BunsEn*. 
i bai my former researches} on the kakodyle compounds I pro- 
ceeded upon the supposition that the base contained in 
them was a ternary radical having the formula C* H® As?; and 
I have done myself the honour of laying before the last meet- 
ing at Plymouth, the results of a very tedious and at the same 
time dangerous series of researches, by which I have proved 
that this radical can not only be separated from its compounds, 
but that it also possesses the property in common and in a 
precisely similar manner with the simple metals, of combi- 
ning directly with the other bodies. If, then, on the one hand 
we arrive at the firm conviction that the theory of organic 
radicals is no longer a hypothetical fiction, but the expres- 
sion of facts which do not allow of any other interpretation, 
the study of the kakodyle series acquires on the other hand” 
an importance with respect to the theory of the science which 
calls for the most careful examination of its compounds. 
I have therefore directed my attention to the higher com- 
pounds of the radical, and have arrived at results no less in- 
teresting, and to which I should the more wish to direct the 
attention of this meeting, as they stand in exact opposition to 
the views which the new French school of chemistry has en- 
deavoured to introduce into the science. 
* Read before the Chemical Section of the British Association at the 
Manchester Meeting and communicated by Prof. Croft. 
+ See Phil. Mag. S. 3. vol. xx. p. 382, 395.—Epir. 
