B 
IV.—CHEMISTRY. 
Arr, LXXXIII.—On a modification of the Mercuro-iodide test for the detection 
of Alkaloidal or Albumenous matters. By Wiuutam Srey, Analyst to 
the Geological Survey of New Zealand. 
[Read before the Wellington Philosophical Society, 24th February, 1877.j 
Waite engaged in making an exhaustive research into the causes which 
prevent the proper action of the mereuro-iodide test when applied to weak 
solution of certain alkaloids, I found that a number of salts are able to dis- 
solve certain of the mercuro-iodides of these alkaloids, and thus prevent the 
formation of those precipitates, which are the indications (unto this test) of 
their presence. Among the salts which have notable effects of this kind are 
potassie iodide and mercuric chloride, and it was therefore found to be a 
matter of great importance that in the preparation of the mercuro-iodide of 
potassium an excess of either be avoided. This is readily accomplished by 
adding the solution of the alkaline iodide to the biehloride of mercury 
until a small quantity of the red precipitate which forms is seen to be per- 
manent, even when well shaken about through the liquid. 
The test liquid prepared in this manner generally has two or three times 
the delicacy of that prepared in the usual way, that is by mixing the neces- 
sary salts in the supposed ratio of their equivalents, this ratio being in 
practise not easy to observe. 
Proseeuting this subject further I found that several of the alkaloids 
and two or three of the albuminoids do not respond to this test, even as 
thus prepared, except they are present in quantity comparatively large, and 
I then ascertained that by the applieation of this test in a still more 
modified form, even such alkaloids and albuminoids can be indicated, 
though present only in minute quantity. This modification is a very simple 
one, and consists in just following up the addition of the mercuric iodide to 
the suspected liquid with one of mercuric chloride in successively minute 
quantities until the liquid is permanently turbid, when in case either of 
these substances is present the precipitate which ultimately forms is of a 
pale yellow colour, instead of a brilliant red, as when alkaloidal or albu- 
minous matters are absent. 
A good way to apply the mercuric chloride is to take a little of its weak 
solution (aqueous) up by a thin glass rod, and dip the rod, with attached 
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