either that the acids were not clean, or they contained objectionable
impurities, or more frequently, the quality of the glycerine used. The
glycerine used for making nitro-glycerine should conform to the following
tests, some of which, however, are of greater importance than others. The
glycerine should--

1. Have minimum specific gravity at 15° C. of 1.261.

2. Should nitrify well.

3. Separation should be sharp within half an hour, without the separation
of flocculent matter, nor should any white flocculent matter (due to fatty
acids) be formed when the nitrated glycerine is thrown into water and
neutralised with carbonate of soda.

4. Should be free from lime and chlorine, and contain only traces of
arsenic, sulphuric acid, &c.

5. Should not leave more than 0.25 per cent. of inorganic and organic
residue together when evaporated in a platinum dish without ebullition
(about 160° C.) or partial decomposition.

6. Silver test fair.

7. The glycerine, when diluted one-half, should give no deposit or
separation of fatty acids when nitric peroxide gas is passed through it.
(Nos. 1, 2, 3, and 5 are the most essential.)

The white flocculent matter sometimes formed is a very great nuisance, and
any sample of glycerol which gives such a precipitate when tried in the