35.00 =
Sodium nitrate NaNO_{3} 16.47 =
Potassium nitrate KNO_{3} 13.86 =
Nitric acid HNO_{3} 22.22 =
Barium nitrate Ba(NO_{3})_{2} 10.72 =

Analysis of Celluloid.—­The finely divided celluloid is well stirred, by means of a platinum wire, with concentrated sulphuric acid in the cup of a Lunge nitrometer, and when dissolved the nitrogen determined in the solution in the usual way.  To prevent interference from camphor, the following treatment is suggested by H. Zaunschirm (Chem.  Zeit., xiv., 905).  Dissolve a weighed quantity of the celluloid in a mixture of ether-alcohol, mixed with a weighed quantity of washed and ignited asbestos, or pumice-stone, dry, and disintegrate the mass, and afterwards extract the camphor with chloroform, dry, and weigh:  then extract with absolute methyl-alcohol, evaporate, weigh, and examine the nitro-cellulose in the nitrometer.

Picric Acid and Picrates.—­Picric acid is soluble in hot water, and to the extent of 1 part in 100 in cold water, also in ether, chloroform, glycerine, 10 per cent. soda solution, alcohol, amylic alcohol, carbon bisulphide, benzene, and petroleum.  If a solution of picric acid be boiled with a strong solution of potassium cyanide, a deep red liquid is produced, owing to the formation of potassium iso-purpurate, which crystallises in small reddish-brown plates with a beetle-green lustre.  This, by reaction with ammonium chloride, gives ammonium iso-purpurate (NH_{4}C_{8}H_{4}N_{5}O_{6}), or artificial murexide, which dies silk and wool a beautiful red colour.  On adding barium chloride to either of the above salts, a vermilion-red precipitate was formed, consisting of barium iso-purpurate.  With ammonio-sulphate of copper, solutions of picric acid give a bright green precipitate.  Mr A.H.  Allen gives the following methods for the assay of commercial picric acid, in his “Commercial Organic Analysis":—­

Resinous and Tarry matters are not unfrequently present.  They are left insoluble on dissolving the sample in boiling water.  The separation is more perfect if the hot solution be exactly neutralised by caustic soda.

Sulphuric Acid, Hydrochloric Acid, and Oxalic Acid, and their salts are detected by adding to the filtered aqueous solution of the sample solutions of the picrates of barium, silver, and calcium.  These salts are readily made by boiling picric acid with the carbonates of the respective metals and filtering:  other soluble salts of these methods may be substituted for the picrates, but they are less satisfactory.

Nitric Acid may be detected by the red fumes evolved on warming the sample with copper turnings.

Inorganic Impurities and Picrates of Potash and Sodium, &c., leave residues on cautious ignition.