paper read before the Society of Chemical Industry (vol. xvi., 1897), in
the place of the potassium iodide starch paper used in the Abel test. The
filter paper used is wetted with a solution of diphenylamine[A] in
sulphuric acid. The solution is prepared as follows:--Take 0.100 grm. of
diphenylamine crystals, put them in a wide-necked flask with a ground
stopper, add 50 c.c. of dilute sulphuric acid (10 c.c. of concentrated
sulphuric acid to 40 c.c. of water), and put the flask in a water bath at
between 50° and 55° C. At this temperature the diphenylamine will melt,
and at once dissolve in the sulphuric acid, when the flask should be taken
out, well shaken, and allowed to cool. After cooling, add 50 c.c. of
Price's double distilled glycerine, shake well, and keep the solution in a
dark place. The test has to be applied in the following way:--The
explosives that have to be tested are finely subdivided, gun-cotton,
nitro-glycerine, dynamite, blasting gelatine, &c., in the same way as at
present directed by the Home Office regulations. Smokeless powders are all
to be ground in a bell-shaped coffee mill as finely as possible, and
sifted as hitherto. 1.5 grm. of the explosive (from the second sieve in
the case of smokeless powder) is to be weighed off and put into a test
tube as hitherto used. Strips of well-washed filter paper, 25 mm. wide,
are to be hung on a hooked glass rod as usual. A drop of the diphenylamine
solution is taken up by means of a clean glass rod, and the upper corners
of the filter paper are touched with it, so that when the two drops run
together about a quarter of the filter paper is moist. This is then put
into the test tube, and this again into the water bath, which has been
heated to 70° C. The heat test reaction should not show in a shorter time
than fifteen minutes. It will begin by the moist part of the paper
acquiring a greenish yellow colour, and from this moment the paper should
be carefully watched. After one or two minutes a dark blue mark will
suddenly appear on the dividing line between the wet and dry part of the
filter paper, and this is the point that should be taken.