otton in the
5 grms. The unconverted cotton must be determined in a separate 5 grms.
and deducted.

The method of determining the soluble cotton now used in the Government
laboratories is as follows:--Fifty grains of the nitro-cotton are
dissolved in 150 c.c. of ether-alcohol, and allowed to stand, with
frequent shakings, in a 200 c.c. stoppered measure for six hours; 75 c.c.
of the clear solution are then drawn off by the aid of a pipette and
evaporated in a dish on the water bath, and finally in the water oven at
120 deg. F. (49 deg. C.), until constant in weight. The weight found equals the
quantity of soluble cotton in the 75 c.c., which, multiplied by 4, equals
the percentage, thus: Suppose that 2.30 grains was the weight found, then

(2.3 x 150)/75 = 4.6 in 50 = 9.20 per cent.

A method for the determination of soluble nitro-cellulose in gun-cotton
and smokeless powder has been published by K.B. Quinan (_Jour. Amer. Chem.
Soc._, 23 [4], 258). In this method about 1 grm. of the finely divided dry
sample to be analysed is placed in an aluminium cup 1.9 inch in diameter
and 4-1/8 inch deep. It is then covered and well stirred with 50 c.c. of
alcohol, 100 c.c. of ether are then added, and the mixture is stirred for
several minutes. After removing the stirrer, the cup is lightly covered
with an aluminium lid, and is then placed in the steel cup of a
centrifugal machine, which is gradually got up to a speed of 2,000
revolutions per minute, the total centrifugal force at the position
occupied by the cups (which become horizontal when in rapid rotation) is
about 450 lbs. They are rotated at the full speed for ten to twelve
minutes, and the machine is then gradually stopped. By this time the whole
of the insoluble matter will be at the bottom of the cup, and the
supernatant solution will be clear. It is drawn off to within a quarter of
an inch of the bottom (without disturbing the sediment), with the aid of a
pipette.

Care must be taken that the solution thus withdrawn is perfectly clear.
About 10 to 15 c.c. of colloid solution and a film of insoluble matter
remain at the bottom of the cup; these are stirred up well, the stirrer is
rinsed with ether-alcohol, about 50 c.c. of fresh ether-alcohol are added;
the mixture is again treated in the centrifugal apparatus for about eight
minutes; the whole washing process is then repeated until all soluble
matter has been removed. This may require about seven or eight (or for
s