DERIVATIVES FROM CAI1BOLIO Aorn.—Of these, the most important is carbazotic, picric, or tri nitrophenic acid (see p. 40). From this acid, are produced several useful compounds employed as dyes, explosives, and therapeutic agents.
Picramic Aoid.—This was obtained in the first instance by Wcehler, by the action of sulphate iron on picric acid, and neutralizing with caustic barytes ; a deep brown salt was produced, from which the baryta was separated by sulphuric acid, leaving an acid which was called " nitrohas matic." But the process by which picramic acid is now manufactured is due to Aime Girard, and depends upon the action of hydrosulphate of ammonia on picric acid. Picramic acid imparts to silk a series of brown tints, similar to those obtained from catechu.
Isopurpurate Potash.—This is obtained by mixing a solution of 2 parts cyanide potassium in 4 parts water, with solution 1 part picric acid in 9 parts boiling water, with constant agitation ; on cooling, it solidifies to a red crystallioe pulp ; this is strained, pressed, triturated, filtered, washed, re dissolved in boiling water, filtered, and left to crystallize, when it forms reddish-brown scales, with a green lustre ; these dissolve in water and alcohol, yielding a purple-red colour.
Isopurpurate ammonia, Murexid, or Soluble Garnet.—This is formed by decomposing isopurpn rate potash by means of ammonium chloride.
Isopurpurate aniline.—This results from a mixture of 42 parts hydrochloride aniline, and 100 parts isopurpurate potash, and yields browns and reds.
Picrates Ammonia, Potash, anol Soda.—These are formed by neutralizing a bot solution picric acid by one of the agents named. Their chief use is owing to their explosive qualities, but the ammonia salt has been highly spoken of as a therapeutic successor to sulphate quinine.
Rosolic Acid, Aurine, or Yellow Coralline.—This may be produced by the direct oxidation of car bolic acid. The process generally adopted for its manufacture is due to Jules Persoz :—A mixture is made of about 3 parts carbolic acid, 2 parts oxalic acid, and 2 parts sulphuric acid. The oxalic
acid is added by degrees, and the whole is heated for some hours at about 160° (320° F.). The heating is best effected by Bunsen burners. During tbe reaction, more or less lively effervescence is produced, due to the disengagement of csabonic oxides, arising from the decomposition of the oxalic acid. The mass thickens and becomes reddish-brown. The operation is terminated when a sample thrown into ammoniacal water dissolves with a reddish-purple colour ; the fire is then with drawn, and the compound is run off by a leaden siphon iuto cold water, to separate the greater part of the excess of sulphuric acid and the sulphophenie acid formed. It is steamed up several times to complete the purification, and is then a pasty cantharides-green mass. This is dried in jacketed enamelled pans, by which it becomes hard and brittle. The whole process occupies about a we,ek. It is soluble in alcohol, but not in water. Dr. Calvert discovered, in 1863, that rosolic acid thus prepared could be employed directly as a dye, and introduced it to dyers under the name of " aurine," and to printers to produce upon silk and albumenized cotton magnificent orange colours, like those of basic chromate of lead, or of turmeric. The calcium lakes of aurine are largely used by paper stainers.
Peonine, or Red Coralline.—In 1860, Persoz discovered that rosolic acid, heated under pressure with ammonia, gave rise to a red substance which he called "Peonine." Gunion, Marnas, and Bossuet perfected the manufacture, and gave it the name of " Red coralline." It is prepared by introducing into a digester 1 part rosolic acid, and about 3 parts commercial ammonia, and heating the mixture with an oil bath for three hours at temperature not exceeding 150° (302° F.). The mass, withdrawn from the apparatus after cooling, forms a thick liquid of golden-crimson colour, which is precipitated on addition of bydrochlorio acid. It imparts a brilliant scarlet to silk and worsted.