272 
WOOD SPIRIT AND ITS DETECTION, 
tiful principle of “dialysis,” as a means of freeing its solution from all saline impurities. 
In order to put this idea to the test of experiment, some of the mercurial solution was 
placed on a dialyser, floating on a considerable bulk of distilled water. After twenty- 
four hours, the diffusate contained a large quantity of chlorine, and but a very small pro¬ 
portion of mercury. The diffusion was then allowed to continue for eight days, during 
which time the water was changed twice a day. On the ninth day a mere trace of 
chlorine could be detected in the diffusate, and but little mercury. The liquid on the 
dialyser was almost odourless and colourless, and of high specific gravity ; it was neutral 
to test-papers, and gave a copious precipitate both on boiling and the addition of acetic 
acid, thus demonstrating that the original compound was still present in the solution, 
apparently unchanged. 
In my subsequent experiments I have found this method of separation most valuable, 
since it enables me to easily purify the colloidal mercurial compound from the crystal¬ 
loids which accompany it in solution. The recapitulation of these, my earliest experi¬ 
ments, is sufficient to show the more important relations of this peculiar compound, and 
likewise enables me to point out how this particular reaction may be made available for 
the detection of “ methylated spirits.” 
Detection of Wood Spirit. —It is a well-known fact that the liquid sold under the 
name of “methylated spirits ” is a mixture of ten per cent, wood-naphtha, and ninety of 
spirit of wine. The addition of the former communicates a very disagreeable taste and 
odour to the latter, thus rendering it unpotable, and, it is said, unfit for internal use. 
This mixed spirit, though easily recognized by its odour when alone, yet, if used in the 
preparation of many strong-smelling tinctures or essences, cannot be thus detected, and 
we are then obliged to resort to chemical means to aid us in the discovery of the adultera¬ 
tion. Up to the present time, but one test has been proposed for the detection of wood- 
spirit ; this is generally known as “ Ure’s test,” having been first mentioned by the emi¬ 
nent chemist of that name. This test simply consists in adding powdered hydrate of 
potash to the suspected liquid ; if wood-spirit be present, the mixture becomes brown in 
about half an hour. That this is a simple, easy, and correct test when the spirit is un¬ 
mixed with vegetable principles, I do not deny; but there is one serious source of error, 
which, I think, prevents it from being generally applicable to the detection of wood- 
spirit in alcoholic tinctures, and this I will now endeavour to make evident. In com¬ 
mencing the examination of a sample of any tincture, it is, of course, necessary to distil 
it, and apply the test to the distillate. We all know that most tinctures contain some 
volatile principles extracted from the plants used in their preparation; when these are 
distilled, the volatile oil, though generally of a high boiling-point, is dissolved in the va¬ 
pour of the spirit, and thus contaminates even the first portions of the distillate. If to this 
we add caustic potash in powder, in many cases the liquid will assume a brown tint, 
even though wood-spirit is not present, owing to the well-know r n action of the alkali 
on many essential oils—thus indicating an adulteration which did not really exist. 
The method which I adopt in testing for w r ood spirit is as follow's:—A small quantity 
of the suspected spirit is placed in a tube retort, and distilled over into a cooled test-tube; 
two or three drops of a very dilute solution of chloride of mercury are now added to the 
distillate, and then excess of solution of caustic potash, and the whole well shaken. If 
the precipitated oxide of mercury does not redissolve even on warming the liquid, wood 
spirit is not present; should complete solution be effected, however, the mixture is 
warmed, and divided into two portions; to one acetic acid is added, which causes the 
formation of a yellowish-white bulky precipitate ; the remaining portion is boiled, and 
a similar precipitate is thrown down, thus proving with certainty that wood naphtha is 
present. In applying this test, it is necessary to be careful not to add too much of the 
mercurial solution, as in that case an insoluble compound would be formed, and, as a 
consequence, a negative result arrived at.* When practised as I have now described, 
I look upon this test as being safe and reliable; at least, so far as my experience with it 
goes, I have always found its indications to be correct, and not liable to the ambiguity 
occasionally occurring with the potash test. I make this statement not on merely theo¬ 
retical grounds, but from information gleaned in the course of a series of comparative 
experiments with pure tinctures, and those purposely adulterated with wood spirit. I 
* It must not be forgotten that oxide of mercury is soluble to a slight extent in potash; 
but such a solution would not yield a precipitate on boiling, or on the addition of an acid. 
