In this way Engelmann was able to determine the evolution of oxygen by
_Euglena_ and by chlorophyl granules.
* * * * *
DETERMINATION OF SMALL QUANTITIES OF ARSENIC IN SULPHUR.
By H SCHAEPPI.
Ten grms. of sulphur, pulverized as finely as possible, are covered
with hot water and a few drops of nitric acid digested for some time,
filtered, and washed till the washings have no longer an acid reaction.
Thus calcium chloride and sulphate are removed, and calcium sulphide, if
present, is destroyed. The sulphur thus prepared is covered with water
at 70 deg. to 80 deg., a few drops of ammonia are added, and the mixture is
digested for a quarter of an hour. All the arsenic present as sulphide
is dissolved, and the ammoniacal liquid is variously treated
according to the degree of accuracy required. For perfectly accurate
determinations the ammoniacal solution is mixed with silver nitrate, and
all the sulphur present in the state of arsenic sulphide is thrown down
as silver sulphide, acidified with nitric acid, filtered, and washed.
The precipitate of silver sulphide is dissolved in hot nitric acid and
determined as silver chloride.
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