DETECTION OF METHYLIC ALCOHOL. 
535 
added. Upon boiling briskly for a few minutes, a small grey precipitate of me¬ 
tallic mercury subsides. 
If these experiments are repeated, using pure methylic alcohol in place of 
rectified spirit, very different results are obtained. The portion of the prepared 
distillate treated with nitrate of silver quickly becomes turbid and opaque when 
treated, and upon boiling a coating of silver sufficiently thick to form a mirror is 
deposited on the inner surface of the tube. If the liquor is transferred to a clean 
tube and again boiled with another grain of nitrate of silver, a part of this is 
also decomposed; and on adding water a considerable precipitate of silver sub¬ 
sides, and a thin film of the metal, which appears broivn by transmitted light, is 
found upon the glasss. Upon boiling the second half of the distillate, after 
adding acetic acici and solution of subnitrate of mercury, fresh portions of the 
latter being supplied as long as it is quickly decomposed, an abundant precipi¬ 
tate of metallic mercury separates. 
In mixtures of etliylic and methylic alcohol the detection of the latter by 
this process is easy and certain, for when it forms only from 1 to 2 per cent, of 
the whole, the distillate, upon treating with nitrate of silver, darkens to opacity, 
and distinctly browns the tube. Of course the spirit to be tested must be free 
from non-volatile organic substances; but the presence of essential oil in small 
quantity is of no moment. Consequently, in applying the method to the exa¬ 
mination of tinctures, etc., a preliminary distillation is often necessary. This, 
however, is a trifling matter ; and for the use of those who may require such 
information, I will briefly describe the simple arrangements which have enabled 
me to perform these small distillations with ease and dispatch. In Fig. 1, a; is a 
two-ounce flask, to which is fitted by means of a sound perforated cork the 
glass tube, b. This tube is about a third of an inch in the bore, and rises two 
inches above the neck of the flask. Its descending limb, c, is connected with 
another two-ounce flask, d, which is immersed to the neck in a vessel of cold 
water. The dish, e, contains water, which is drawn off by a piece of lamp-wick, 
and deposited by drops on the tube, c, round which is rolled a slip of blotting- 
paper, thus forming an effectual condenser. The most convenient lamp is an 
argand burner with iron chimney, on the top of which fits a cap having a hole 
in its centre about the size of a shilling. Fig. 2 represents an ounce flask con¬ 
nected with a test-tube receiver. It may be held by a tube-clip, and is useful 
for distilling small quantities of spirit from tinctures, etc. 
Supposing, then, it is required to test, say Tinct. Benzoin. Co. for methylic 
alcohol: introduce a drachm or two into the flask, wrap some wet blotting- 
paper round the test-tube, apply heat, and in a few minutes the first operation 
is finished. Now put into the flask, a (Fig. 2), 30 grains'of bichromate of 
potash in powder, add half an ounce of water with 25 jminims of strong sul¬ 
phuric acid, and then half a fluid drachm of the spirit. Allow the mixture to 
stand fifteen minutes, and distil half a fluid ounce. Add to the distillate a 
very slight excess of carbonate of soda, boil it down to two fluid drachms, and 
add enough acetic acid to impart a distinct though feeble acid reaction; then 
pour it into a test-tube, and after adding a grain of nitrate of silver dissolved 
in half a drachm of water, boil very gently for about two minutes. If the 
liquor merely darkens a little, but continues quite translucent, the spirit is free 
from methyl; but if it becomes muddy and opaque, and the tube after being 
rinsed and filled with water appears browned (best seen by holding it against 
white paper), the spirit is methylated. In the cases of tinctures prepared with 
proof spirit, about 50 minims of the distillate should be taken for oxidation. 
A preparatory distillation is not always needful. Spt. Ammon. Aromat. only 
requires neutralizing with sulphuric acid, and filtering from the sulphate of 
ammonia. Strong solutions of essential oil, as some of the “ spirits ” of the 
Pharmacopoeia, may be diluted with 7 parts of water, shaken with magnesia, 
