sulphite of soda, citric acid. Solubility: I in 2 of water, the resulting solution measuringin 10 of alcohol; it is also
soluble in glycerine and ether.
Pyroxyline (Ger., Pyroxylin, Collodiumwolley Scheissbaum-wolle; Fr., Pyroxyle; Ital., Cotone Fulminante, Pirossilina). A substance of variable composition obtained by acting upon cellulose C6H10O5, with a mixture of nitric and sulphuric acids, and in this process one or more atoms of hydrogen are replaced by N02. The following directions for preparing it are taken from Hardwich's " Photographic Chemistry," but the author would advise anybody who requires small quantities to buy it ready made, rather than prepare it for his own use, as the operation is not very easy, and the acids are dangerous to handle : -
Pour the water into a dish, add the nitric acid, and lastly the sulphuric acid. The mixture must be well stirred, and the temperature, which is raised by the addition of the sulphuric acid, should be allowed to sink to 1500 F., at which heat the mixture must be kept by means of a water bath. The wool must be first put in a strong solution of carbonate of soda or potash to free it from its natural oil, and then washed in plain water till the washings show not the slightest trace of alkalinity or the salt used, and dried. The prepared wool should be then weighed out into balls of about thirty grains each, and immersed one by one into the mixture of acids, and well stirred up, care being taken that each little ball is thoroughly saturated with acid; they should be left for ten minutes, and then taken out and washed in running water for twenty-four hours, or till they show no acid reaction with litmus; they can be then dried in the sun, or on a water bath. The resulting production should be entirely soluble in a mixture of equal parts of alcohol and ether, and also inflammable. The nitric acid alone acts upon the cotton, the sulphuric causing this action to be much more rapid. This action of the sulphuric acid is said to be catalytic. A special kind of pyroxyline, called celloidin, has been introduced by Dr. Schering, of much greater purity than the other, and