546 
ON LIQUOU HYDRARGYRI PERCHLORIDI, B.P. 
gives a white precipitate with nitrate of silver, proving the presence of chlo¬ 
rine. It is entirely volatilized by heat without being first fused, and part is 
sublimed on the upper side of the test-tube when held aslant. This white 
sublimate is calomel, as it is blackened on the addition of liquor potass#, 
forming mercurous oxide; and the filtered fluid from this, acidulated with 
nitric acid, gives, with nitrate of silver, a white precipitate,—thus proving 
the sublimate to be mercurous chloride. These characteristic tests sufficiently 
show" that the precipitate formed in the Pharmacopoeia solution, made with 
common water, is the true hydrargyrum ammoniatum or white precipitate of 
the Pharmacopoeia. 
Its formation is due to the presence of lime in the water, which splits up 
the double salt, abstracts chlorine from it, forming chloride of calcium, which 
is retained in solution, and throws down the precipitate. Supposing the 
action to be due to carbonate of lime, which is always held in solution in 
common water, the decomposition would be represented by the following 
equation :— 
2 NH.Cl. HgCl 9 H 2 O + CaC0 3 = NIL,HgCl 4- N H 4 Cl + CaCl 2 
+ C0 2 + 2 H 2 0. 
The same reaction takes place in making a solution of the crystallized 
ammonio mercuric chloride in either common water or lime-water, showing 
tnat the precipitate is not caused by the lime setting free ammonia from the 
excess of chloride of ammonium in the Pharmacopoeia solution. 
Seeing that there is no precipitate formed in the solution made with water 
free from lime, and that perchloride of mercury is perfectly soluble in water 
holding carbonate of lime in solution* (with lime-water it, of course, throws 
down mercuric oxide, as in making lotio hydrargyri flava), from the above 
experiments it may be deduced that (1) liquor hydrargyri perchloridi, B.P., 
does contain a double salt in solution ; (2) this double salt is the ammonio- 
mercurio chloride, or sal alembroth ; and (3) lime-water is a test for its pre¬ 
sence, as it throws down a white precipitate with the double salt, and with 
the perchloride alone in solution it gives a yellow precipitate. 
The precipitate obtained from one pint of the B.P. liquor, made with New 
Biver water, weighed 2'7 grains, bearing the ratio of 27 to 100 of the per¬ 
chloride used in the first instance ; thus upwards of one-fourth was converted 
into white precipitate, and if it were diluted, as it generally is when taken, 
with more water, which would yield a further supply of lime, eventually a 
point would arrive when the whole of the perchloride would be converted 
into the insoluble white precipitate ! To corroborate this by experiment, I 
found that the filtrate from the above precipitate, diluted with more New 
Biver water, freely eliminated more of the precipitate. 
The importance of the bearing of these facts on therapeutics cannot be 
overrated. Here we have one of the most active corrosive poisons rendered 
a comparatively inert and doubtful one, and its chemical and physical cha¬ 
racters, and very probably its medicinal action, completely altered by tne 
mere substitution of common water for distilled, as is too often done in dis¬ 
pensing. This is, in fact, inevitable in hospitals, and it is in these where this 
solution is principally prescribed, it being almost impossible to obtain a suf¬ 
ficient supply to dispense all their medicines with distilled water, f • 
The writer of this was led to make these investigations through a mistake. 
* “ The carbonates of barium, strontium, and calcium precipitate mercuric oxide from the 
solutions of mercuric sulphate and nitrate, but not from mercuric chloride .” (Watts s 
‘ Dictionary of Chemistry,’ vol. iii. p. 900 .) 
f Yet such is done at the largest hospital in London. I allude to the lately much-abused 
St. Bartholomew’s. 
