The cotton, which is generally packed wet in zinc-lined wooden boxes, will require to be dried, as it is very essential indeed that none of the materials used in the manufacture of gelatine should contain more than the slightest trace of water.  If they do, the gelatine subsequently made from them will most certainly exude, and become dangerous and comparatively valueless.  It will also be much more difficult to make the nitro-cotton dissolve in the nitro-glycerine if either contains water.

In order to find out how long any sample of cotton requires to be dried, a sample should be taken from the centre of several boxes, well mixed, and about 1,000 grms. spread out on a paper tray, weighed, and the whole then placed in the water oven at 100 deg.  C., and dried for an hour or so, and again weighed, and the percentage of moisture calculated from the loss in weight.  This will be a guide to the time that the cotton will probably require to be in the drying house.  Samples generally contain from 20 to 30 per cent. of water.  After drying for a period of forty-eight hours, a sample should be again dried in the oven at 100 deg.  C., and the moisture determined, and so on at intervals until the bulk of the cotton is found to be dry, i.e., to contain from 0.25 to 0.5 per cent. of moisture.  It is then ready to be sifted.  During the process of removing to the sifting house and the sifting itself, the cotton should be exposed to the air as little as possible, as dry nitro-cotton absorbs as much as 2 per cent. of moisture from the air at ordinary temperatures and average dryness.

The drying house usually consists of a wooden building, the inside of which is fitted with shelves, or rather framework to contain drawers, made of wood, with brass or copper wire netting bottoms.  A current of hot air is made to pass through the shelves and over the surface of the cotton, which is spread out upon them to the depth of about 2 inches.  This current of air can be obtained in any way that may be found convenient, such as by means of a fan or Root’s blower, the air being passed over hot bricks, or hot-water pipes before entering the building.  The cotton should also be occasionally turned over by hand in order that a fresh surface may be continually exposed to the action of the hot air.  The building itself may be heated by means of hot-water pipes, but on no account should any of the pipes be exposed.  They should all be most carefully covered over with wood-work, because when the dry nitro-cotton is moved, as in turning it over, very fine particles get into the air, and gradually settling on the pipes, window ledges, &c., may become very hot, when the slightest friction might cause explosion.  It is on this account that this house should be very carefully swept out every day.  It is also very desirable that the floor of this house should be covered with oilcloth or linoleum, as being soft, it lessens the friction.