amples with much insoluble matter ten or twelve or more) washings, but as
the extraction proceeds, the period of rotation may be somewhat reduced.
After extraction is completed, the insoluble matter is transferred to a
Gooch crucible with the usual asbestos pad, dried at 100 deg. C., and weighed.
The residue may, if wished, be dried and weighed in the aluminium cup, but
then it cannot be ignited. The whole time for an analysis exclusive of
that required for drying, is from one to two hours--average time, 1-1/4
hour. The results are satisfactory both as to accuracy and rapidity.
Acetone-soluble nitro-cellulose may be determined by the same method.

~The Unconverted or Non-nitrated Cotton.~--However well the cotton has
been nitrated, it is almost certain to contain a small quantity of non-
nitrated or unconverted cotton. This can be determined thus:--Five grms.
of the sample are boiled with a saturated solution of sodium sulphide, and
then allowed to stand for forty-eight hours, and afterwards filtered or
decanted, and again boiled with fresh solutions of sulphide, and again
filtered, washed first with dilute HCl and then with water, dried, and
weighed. The residue is the cellulose that was not nitrated, plus ash, &c.
It should be ignited, and the weight of the ash deducted from the previous
weight.

Acetone, and acetic-ether (ethyl-acetate) may also be used as solvents for
the nitro-cellulose. Another process is to boil the gun-cotton, &c., in a
solution of sodium stannate made by adding caustic soda to a solution of
stannous chloride, until the precipitate first formed is just
re-dissolved. This solution dissolves the cellulose nitrates, but does not
affect the cellulose. Dr Lunge found the following process more
satisfactory in the case of the more highly nitrated products:--The
reagent is an alcoholic solution of sodium-ethylate prepared by dissolving
2 to 3 grms. of sodium in 100 c.c. of 95 per cent. alcohol, and mixing the
filtered solution with 100 c.c. of acetone. It has no effect upon
cellulose, but decomposes nitro-cellulose with the formation of a reddish
brown compound, which is soluble in water. In the determination, 5 grms.
of gun-cotton are heated to 40 deg. or 50 deg. C. on the water bath with 150 c.c.
of the reagent, the liquid being shaken at intervals for twenty to thirty
minutes; or the mixture may be allowed to stand for a few hours at the
ordinary temperature. The brown-red solution is decanted from t