PRESENCE OF ARSENIC IN PHOSPHORUS. 
333 
M. Liebig, in repeating the experiments of MM. Barwald 
and Wittstock, ascertained that phosphorus purchased at 
Francfort also contained a considerable quantity of arsenic. 
He also verified the assertion of these chemists, that in the 
oxygenation of phosphorus, by diluted nitric acid, there was 
principally a formation of phosphorous acid; and also that 
when this acid solution is evaporated, to get rid of the nitric 
acid, at a certain degree of concentration, there is a formation 
of phosphuretted hydrogen, which reduces all the arsenic or 
arsenious acid present; hence there is a deposition of a heavy 
black powder; this is metallic arsenic. This able chemist, 
therefore, proposes, in the purification of phosphoric acid, to 
use phosphorous acid instead of sulphuretted hydrogen, as the 
latter sometimes requires several days before it completely 
fulfils the intention. His plan is as follows: two parts of 
phosphorus are to be oxygenized by diluted nitric acid, the so- 
lution evaporated to drive off the nitric acid, until the arsenic 
is deposited. At the same time, one part of phosphorus in 
cylinders contained in glass tubes, is to be placed in a funnel, 
in a cellar, and the phosphatic acid (a mixture of phosphorous 
and phosphoric acids,) thus obtained, is to be used to purify 
the phosphoric acid; for this purpose the latter is to be diluted 
with a little water, filtered, the phosphatic acid added, and the 
whole evaporated; if any arsenic is deposited, the process is 
to be repeated. Journ. cle Pharm. 
