This quantity is equivalent to 1¼ ounce Troy or Apothecaries' weight;—and to 1¼ ounce Avoirdupois weight plus 54 grains. Place this in a teacup or any other convenient vessel, and pour upon it.
| Water | 1½ | fluid drachms | |
| mixed with | Oil of Vitriol | 12 | " |
Stir well with a glass rod for two or three minutes, until all effervescence has ceased, and an even, pasty mixture, free from lumps, is obtained.
During the whole process, abundance of dense fumes of Nitric Acid will be given off, which must be allowed to escape up the flue or into the open air.
A modification of the formula.—The above formula will invariably succeed with a good sample of acid and pure Nitre. When tried however with Oil of Vitriol rather weaker than ordinary, and commercial Nitre, it may fail, the cotton being gelatinized and dissolved. When such is the case, the addition of water must be omitted or the quantity reduced from one drachm and a half to half a drachm.
GENERAL DIRECTIONS FOR IMMERSING, WASHING, AND DRYING THE PYROXYLINE.
The mixture of Sulphuric Acid and Nitre requires to be used immediately after its preparation, as it solidifies into a stiff mass on cooling; but the mixed acids may be kept for any length of time in a stoppered bottle.
When Cotton is used, the fibres should be well pulled out, and small tufts added one by one to the acid mixture, stirring with a glass rod in order to keep up a constant change of particles. The Paper is cut into squares or strips, which are introduced singly.
In either case the quantity must not be too great, or some portions will be imperfectly acted upon; about 20 grains to each fluid ounce of the mixture will be sufficient.
The time of immersion required varies from ten minutes with Cotton, to twenty minutes or even half an hour with the Paper. When an unusually large proportion of Sulphuric Acid is used, as in the case of a weak sample of Nitric Acid, the Cotton should be removed at the expiration of six or seven minutes, as there is a tendency to partial solution of the Pyroxyline in the acid mixture under those circumstances.