382 - M. C. Lea on Picric Acid. 
The whole of this operation may be carried on in the labora- 
tory without a perceptible escape of acid vapor. A cork in the 
neck of the wide-mouthed flask with a long-necked funnel, and 
a bent glass tube sufficiently long to reach within a few inches 
of the bars of a grate or the air-draft of a stove, will effect this 
object. By inclining the tube and placing a vessel under its end, 
a large quantity of nitric acid may be collected, which may be 
cohobated, and serve to reduce the quantity of fresh acid em- 
ployed, remembering, however, that it is very weak, having a 
specific gravity varying from 1-1 to 1-2. 
This process might doubtless be extended to other materials, 
such as aloes, indigo, the refuse of gum bezoin after sublimation 
of benzoic acid, &. It does not require more time than the 
ordina : 
The purification of the crude picric acid is best effected as 
follows: The crude acid is well stirred up with a small quantity 
pe 
sulphuric acid added in the proportion of eight or ten drops to 
each pint of solution, which is boiled for a few minutes, and 
rapidly filtered through a heated filter. It is convenient to filter 
into a POTTS dish over a lamp. The picric acid is then neu- 
tralized with carbonate of pean or preferably with solution of 
crystallized bicarbonate, as a troublesome second filtration 18 
thus saved. When the potash salt crystallizes out it is to 
thoroughly freed from the mother water and recrystallized. If 
desired to have a very pure product, it may be boiled with ant 
mal charcoal and recrystallized several times. The potash salt 
is decomposed in a boiling solution with chlorhydric acid, and 
the picric acid, when thoroughly freed from adhering chlorid of 
potassium, is pure. 
In addition to the reducing agents already known to be capa 
to pale yellow, the picramic acid having exchanged an atom of 
Nie fe one of NOs. This reaction affords an extremely deli- 
cate test for the presence of a cyanid. 
_ Picrate of Baryta.—By slow evaporation yields prismatic crys- 
tals, which are dichromatic. In the evaporating basin they pre 
the appearance of yellow prisms with red summits. ; 
AD leche of oe dissolves rea a 
) By heating on platinum foil 1 
ee 2 
um fo 
