ains nothing but
nitroprusside and nitrate of potash or soda. The nitrates being the
least soluble, are first crystallized, and the remaining liquid, on
farther evaporation, yields crystals of the nitroprusside. The sodium
salt crystallizes most easily.--(PLAYFAIR.)
As some substances, particularly in complicated compounds, are not
detected with sufficient nicety in the dry way of analysis, it will
often be necessary to resort to the wet way. It is therefore necessary
to have prepared the reagents required for such testing, as every
person, before he can become an expert blowpipe analyst, must be
acquainted with the characteristic tests as applied in the wet way.
* * * * *
Part II.
INITIATORY ANALYSIS.
Qualitative analysis refers to those examinations which relate simply
to the presence or the absence of certain substances, irrespective of
their quantities. But before we take cognizance of special
examinations, it would facilitate the progress of the student to pass
through a course of Initiatory Exercises. These at once lead into the
special analysis of all those substances susceptible of examination by
the blowpipe. The Initiatory Analysis is best studied by adopting the
following arrangement:
1. EXAMINATIONS WITH THE GLASS BULB.
The glass of which the bulb is made should be entirely free from lead,
otherwise fictitious results will ensue. If the bulb be of flint
glass, then by heating it, there is a slightly iridescent film caused
upon the surface of the glass, which may easily be mistaken for
arsenic. Besides, this kind of glass is easily fusible in the
oxidating flame of the blowpipe, while, in the reducing flame, its
ready decomposition would preclude its use entirely. The tube should
be composed of the potash or hard Bohemian glass, should be perfectly
white, and very thin, or the heat will crack it.
The tube should be perfectly clean, which can be easily attained by
wrapping a clean cotton rag around a small stick, and inserting it in
the tube. Before using the tube, see also that it is perfectly dry.
The quantity of the substance put into the tube for examination should
be small. From one to three grains is quite sufficient, as a general
rule, but circumstances vary the quantity. The sides of the tube
should not catch any of the substance as it is being placed at the
bottom of the tube, or into the bulb. If any of the powder, however,
should adhere
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