[Illustration:  FIG. 46.—­HEAT TEST APPARATUS.]

Professor C.E.  Munroe, of the U.S.  Torpedo Station, has determined the firing point of several explosives by means of this apparatus.

The Government Heat Test (Explosives Act, 1875):  Apparatus required.—­A water bath, consisting of a spherical copper vessel (a), Fig. 46, of about 8 inches diameter, and with an aperture of about 5 inches; the bath is filled with water to within a quarter of an inch of the edge.  It has a loose cover of sheet copper about 6 inches in diameter (b) and rests on a tripod stand about 14 inches high (c), which is covered with coarse wire gauze (e), and is surrounded with a screen of thin sheet copper (d).  Within the latter is placed an argand burner (f) with glass chimney.  The cover (b) has four holes arranged, as seen in Fig.  II., No. 4 to contain a Page’s[A] or Scheibler’s regulator, No. 3 the thermometer, Nos. 1 and 2 the test tubes containing the explosive to be tested.  Around the holes 1 and 2 on the under side of the cover are soldered three pieces of brass wire with points slightly converging (Fig.  III.); these act as springs, and allow the test tubes to be easily placed in position and removed.

[Footnote A:  See Chem.  Soc.  Jour., 1876, i. 24.  F.J.M.  Page.]

Test Tubes, from 5-1/4 to 5-1/2 inches long, and of such a diameter that they will hold from 20 to 22 cubic centimetres of water when filled to a height of 5 inches; rather thick glass is preferable.  Indiarubber stoppers, fitting the test tubes, and carrying an arrangement for holding the test papers, viz., a narrow glass tube passing through the centre of the stopper, and terminating in a platinum wire hook.  A glass rod drawn out and the end turned up to form a hook is better.

The Thermometer should have a range from 30 deg. to 212 deg.  F., or from 1 deg. to 100 deg.  C. A minute clock is useful.

Test Paper.—­The test paper is prepared as follows:—­45 grains (2.9 grms.) of white maize starch (corn flour), previously washed with cold water, are added to 8-1/2 oz. of water.  The mixture is stirred, heated to boiling, and kept gently boiling for ten minutes; 15 grains (1 grm.) of pure potassium iodide (previously recrystallised from alcohol, absolutely necessary) are dissolved in 8-1/2 oz. of distilled water.  The two solutions are thoroughly mixed and allowed to get cold.  Strips or sheets of white English filter paper, previously washed with water and re-dried, are dipped into the solution thus prepared, and allowed to remain in it for not less than ten seconds; they are then allowed to drain and dry in a place free from laboratory fumes and dust.  The upper and lower margins of the strips or sheets are cut off, and the paper is preserved in well-stoppered or corked bottles, and in the dark.  The dimensions of the pieces of test paper used are about 4/10 inch by 8/10 inch (10 mm. by 20 mm.).[A]