y pressed into small cylinders
(about 3 in. diameter and 4 in. high) whilst wet, and these are
carefully dried before the nitro-glycerin is added. The pressure applied
is only sufficient to make the gun-cotton just hold together so that it
is easily mixed with the nitro-glycerin. The mineral jelly or vaseline
is obtained at a certain stage of distillation of petroleum, and is a
mixture of hydrocarbons, paraffins, olefines and some other unsaturated
hydrocarbons, possibly aromatic, which no doubt play a very important
part as preservatives in cordite.

The stability of cordite, that is, its capability of keeping without
chemical or ballistic changes, is judged of by certain "heat tests." The
Abel heat test consists in subjecting a weighed quantity, 2 grams, of
the finely divided cordite contained in a test tube, to a temperature of
70 deg. C. maintained constant by a water bath. The test tube is about 6
X 3/4 in., and dips into the water sufficiently to immerse about 2 in.,
viz. the part containing the cordite. In the upper free portion a piece
of filter-paper impregnated with a mixture of potassium iodide and
starch paste is suspended by a platinum wire from the stopper of the
tube. A portion of the test paper is moistened with a solution of
glycerin to render it more sensitive than the dry part. A faint brown
colour appearing on the moistened portion indicates that some oxides of
nitrogen have been evolved from the cordite. This brown tint is compared
with a standard, and the time taken before the standard tint appears is
noted. The time fixed upon as a test of relative stability is an
arbitrary one determined by examination of well-known specimens. Should
the cordite or other explosive contain traces of mercury salts, such as
mercuric chloride, which is sometimes added as a preservative, this test
is rendered nugatory, and no coloration may appear (or only after a long
exposure), although the sample may be of indifferent stability. It is
now customary to examine specially for mercury, either by heating the
explosive in contact with gold leaf or silver foil, or by burning the
substance and examining the flame in the spectroscope.

The method of examination known as the vacuum silvered vessel process is
probably not interfered with by the presence of very small quantities of
mercury. It consists in heating 50 grams of the finely divided explosive
in a Dewar's silvered vacuum glass bulb to a rigidly constant
temperature