[Footnote A:  Ketones are derived from the fatty acids by the substitution of the hydroxyl of the latter by a monad positive radical.  They thus resemble aldehydes in constitution.  The best-known ketone is acetone CH_{3}CO.CH_{3}.  Mixed ketones are obtained by distilling together salts of two different fatty acids.  Thus potassic butyrate and potassic acetate form propyl-methyl-ketone—­

C(C_{2}H_{5})H_{2}
|
CO.CH_{3}]

The solvents of pyroxyline can be divided into general classes—­First, those which are solvents without the aid of heat or solution in alcohol; second, those that are solvents when dissolved in alcohol.  These solvents are those which also develop a solvent action when heated to their melting point in combination with pyroxyline.

Mr W.D.  Field groups the solvents of pyroxyline into classes thus:  Two of the monohydric alcohols; compound ethers of the fatty acids with monohydric alcohols, aldehydes; simple and mixed ketones of the fatty acid series.  These four classes include the greater number of the solvents of pyroxyline.  Those not included are as follows:—­Amyl-nitrate and nitrite, methylene-di-methyl ether, ethidene-diethyl ether, amyl-chloracetate, nitro-benzene and di-nitro-benzene, coumarin, camphor, glacial acetic acid, and mono-, di-, and tri-acetin.

Richard Hale uses the following solvent:—­Amyl-acetate, 4 volumes; petroleum naphtha, 4 volumes; methyl-alcohol, 2 volumes; pyroxyline, 4 to 5 ounces to the gallon of solvent.  Hale used petroleum naphtha to hasten the drying qualities of the varnish, so that it would set on the article to be varnished before it had a chance to run off.  It is, however, the non-hygroscopic character of the solvent that makes the varnish successful.  This formula is very largely used for the production of pyroxyline varnish, which is used for varnishing pens, pencils, &c., also brass-work and silver-ware.

The body known as oxy-cellulose[A] is formed by the action of nitric acid upon cellulose when boiled with it.  The quantity formed is about 30 per cent. of cellulose acted upon.  When washed free from acid, it gelatinises.  It is then soluble in dilute alkalies, and can be reprecipitated from solution by alcohol, acids, or saline solutions.  Messrs Cross and Bevan assign to it the formula C_{18}H_{26}O_{16}.  It dissolves in concentrated sulphuric acid, and with nitric acid forms a nitro body of the formula C_{18}H_{23}O_{16}3(NO_{2}), which is prepared as follows:—­The gelatinous oxy-cellulose is washed with strong nitric acid until free from water, and is then diffused through a mixture of equal volumes of strong sulphuric and nitric acids, in which it quickly dissolves.  The solution, after standing for about an hour, is poured in a fine stream into a large volume of water, by which the “nitro” body is precipitated as a white flocculent mass.  The product, after drying at 110 deg.  C., was found upon analysis to contain 6.48 per cent. nitrogen.