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 deg.  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.

[Footnote A:  Dr G. Spica (Rivista, Aug. 1897) proposes to use hydrochloride of meta-phenylenediamine.]

Exudation and Liquefaction Test for Blasting Gelatine, Gelatine Dynamite, &c.—­A cylinder of blasting gelatine, &c., is to be cut from the cartridge to be tested, the length of the cylinder to be equal to its diameter, and the ends being cut flat.  The cylinder is to be placed on end on a flat surface without any wrapper, and secured by a pin passing vertically through its centre.  In this condition the cylinder is to be exposed for 144 consecutive hours (six days and nights) to a temperature ranging from 85 deg. to 90 deg.  F. (inclusive), and during such exposure the cylinder shall not diminish in height by more than one-fourth of its original height, and the upper cut surface shall retain its flatness and the sharpness of its edge.

Exudation Test.—­There shall be no separation from the general mass of the blasting gelatine or gelatine dynamite of a substance of less consistency than the bulk of the remaining portion of the material under any conditions of storage, transport, or use, or when the material is subjected three times in succession to alternate freezing and thawing, or when subjected to the liquefaction test before described.

Picric Acid.—­The material shall contain not more than 0.3 part of mineral or non-combustible matter in 100 parts by weight of the material dried at 160 deg.  F. It should not contain more than a minute trace of lead.  One hundred parts of the dry material shall not contain more than 0.3 part of total (free and combined) sulphuric acid, of which not more than 0.1 part shall be free sulphuric acid.  Its melting point should be between 248 deg. and 253 deg.  F.

Ammonite, Bellite, Roburite, and Explosives of similar Composition.—­ These are required to stand the same heat test as compressed nitro-cellulose, gun-cotton, &c.

Chlorate Mixtures.—­The material must not be too sensitive, and must show no tendency to increase in sensitiveness in keeping.  It must contain nothing liable to reduce the chlorate.  Chlorides calculated as potassium chloride must not exceed 0.25 per cent.  The material must contain no free acid, or substance liable to produce free acid.  Explosives of this class containing nitro-compounds will be subject to the heat test.