MISCELLANY. 
179 
"If the liquids are perfectly neutral, at the moment when they are 
mixed, a subnitrate of mercury is precipitated, which cannot be removed 
by the most careful washing, and which produces dangerous effects when 
this preparation is employed internally." — Berzelius. 
Mialhe has found — 
1. That sublimed calomel and white precipitate have no appreciable 
difference. 
2. I'he solubility of the two chlorides appears the same. 
3. The precipitate afforded only traces of chloride of sodium. 
4. In two specimens, prepared according to the French codex^ he de- 
tected subnitrate of mercury; but in two other specimens he could find 
none ; of the two latter, one had been prepared by decomposing the nitrate 
by common salt ; and the other, by hydro-chloric acid. In the present 
case, therefore, a basic nitrate was used. Journal de Pharniacie. 
On a JSeiu Test for Nitric Jcid, by J. W. Bailey, Acting Prof, of 
Chem. &c., U, S. Military Academy. Chemical reagents may be divided 
into two classes ; first, those which produce with the substance they are 
employed to detect, an action which they will produce with no other 
known body; an example is starch, as a test for free iodine : secondly, 
those which cause a certain action with a small number of bodies, which 
they will not exhibit with any others ; as, for example, sulphuretted hy- 
drogen, which causes a black precipitate with zfew metals. 
The first class are, of course, the most valuable reagents, as they require 
no subsequent operation to determine whether certain substances are pre- 
sent or not ; while with those of the second class, we only determine that 
one of a certain number of bodies must be present, but must then resort 
to other means to ascertain which particular one it may be. 
There are many cases, however, when we may know that only one of 
those bodies which are capable of giving similar results with the reagent 
added is present, and then if this result «5 produced, the evidence is as 
satisfactory as can be desired. 
The test which I would propose, must be placed among those of the 
second class, and is therefore inferior in value to morphia as a reagent for 
nitric acid ; but I think it at least as valuable as the method by means of 
gold leaf and hydrochloric acid, or by the bleaching of indigo. 
The substance I now suggest, as a new reagent for nitric acid, is the 
cyano-hydrargyrate of iodide of potassium, discovered by M. Galliot. It 
is formed by mixing together bicyanuret of mercury and iodide of potas- 
sium, (one equivalent of each,) dissolved in small quantities of warm 
water. It soon crystallizes in a very beautiful manner. This is the same 
salt which has recently been recommended as a means of detecting the 
presence of hydrochloric acid in hydrocyanic acid. (See Lond. and Ed. 
Phil. Mag. Nov. 1835,) 
lis use as a test for nitric acid depends upon the faci> that if one of the 
Sicale-like crystals be introduced jnto moH acids, it immediately becomes 
