L. F. Wood—Arsenic as Pyroarseniate of Magnesia. 369 
d 
solution of MgCl, was now added as long as the formation of a 
precipitate continued, and then an additional quantity of about 
1} c.c. was added, and the mixture allowed to stand over night. 
A quantity of aleohol (85 per cent) equal in bulk to one-half 
the liquid was then added, and the precipitate was filtered upon 
a weighed filter and washed with a mixture composed of about 
2 parts alcohol, 1 part strong ammonia water and 3 parts water. 
n each case, when taking the weight of the filter, it was 
nearly balanced on the opposite scale-pan by another filter of 
Was to avoid spattering and to keep away reducing gases. 
also served to protect the wearing of the crucible, as at the end 
of seven analyses the small crucible did not differ in weight 
rom its first time weighing. 
The crucibles were finally heated over the blast ~— vi 
in 
the products of decomposition of nitrate of ammonium are 
oxidizing agents, there is little reason to fear a reduction of 
from the weicht: i ia in the crucible 
ghts of pyroarseniate of magnesia ’ 
and from the weigh of hydrated arseniate left upon the filter. 
I. Filtrate = 137 c.e. Washwater = 54 ¢.¢. 
Weight of Mg,As,O = 0°4637 grams. 
. MgNH,'AsO,+Aq = 0076 “ 
* “ 
As,O, equiv. in weight = 0°30005 
“M Jour, en Vor. VI, No. 35.—Nov., 1873. 
