Amide-an-naphthalene, N2 { 1°G1176.NH2, is produced by adding potassium nitrite to a solution of amido-naphthalene hydrochloride. It crystallizes iu orange needles, with a beetle-green lustre; its salts, which are decomposed by water, have an intense violet colour. It dyes silk a fine orange, turning purple when dipped into hydrochloric acid, and becoming again yellow when washed with w ater.
Sulpho-acide of Naphthalene.—When naphthalene is heated with concentrated sulphuric acid, three sulpho-acids are formed, viz. :—monosulpho-naphthalic acid, of which there are two modifica tions (a and 13), and bisulpho-naphthalic acid. By heating 5 parts naphthalene and 4 parts acid for some time in a salt-water bath, the mixture will contain principally the a modification of the mono-acid ; but if the heat is carried to 116°-118° (240°-245° F.), it will yield the 13 modifica tion. The acids are first freed from the unaltered naphthalene, by pouring the boiling mixture into a large quantity of water : the naphthalene separates out on cooling ; the excess of sulphuric acid is removed by boiling with a little chalk, filtered to remove the sulphate of lime ; the filtrate yields crystals of sulpho-naphthalic acid on concentration ; the acids are separated by conversion into lime salts, the latter being difficultly soluble, whilst the former rernains in the mother-liquor. The disulpho-acid is obtained by heating for several hours 1 part naphthalene and 5 acid. The removal of the sulphuric acid can be-effected by oxide of lead, the sulphate of lead being insoluble, whilst the sulpho-naphthalic salts are separated by their differences of solubility in water and alcohol. The free acids are obtained by decomposing the lead solutions by sulphuretted hydrogen.
These acids form the starting-point in the production of several compounds which have been worked upon more or less for tinctorial products. The conversion of these acids into naphthalic alcohol, or naphthol, is thus accomplished :—Sulpho-naphthalic acid is neutralized with potash, after separation of the unaltered naphthalene ; the salt thus obtained is fused with caustic potash or soda ; by the addition of dilute acids to the aqueous solutions, the naphthol is precipi tated in a crystalline form, of which there are two modifications, corresponding with the sulpho-acids.
Naphthalene Chloritles.—Naphthalene melts and absorbs chlorine when the latter is passed over it ; the dichloride, which is first formed, is a heavy pale-yellow oil ; by repeated distillation, and the action of alcoholic potash, it is resolved into hydrochloric acid and mono-chloro-naphthalene.
The continued action of chlorine converts the dichloride into tetra-chloride.
Naphthalene Dichlorhydrate, 0,0E12 VoltD2, is obtained by dissolving naphthalene in concentrated hypochlorous acid. Naphthalene, treated in the cold with a mixture of hydrochloric acid and chlorate of potash, is transformed into naphthalene dichloride, and di-chloro-naphthaquinone.
Phthalio Anhydride. C2E1402.—This is produced by the action of nitric acid on dichloride of naphthalene. When the dichloride of naphthalene is treated with boiling nitric aoid, it dissolves slowly, with evolution of nitrous acid. The solution deposits crystals on cooling. These crystals are purified by recrystallization from boiling water : the mother-liquor contains oxalic acid. Pure phthalic acid crystallizes in white nacreous laminas, arranged in rounded groups. It is sparingly soluble in cold water, but dissolves easily in alcohol and ether. By distillation, it is converted into Ththalic anhydride.
Anthracene, or Paranaphthalene. C„11,..—This substance is the last product of com mercial importance obtained in the distillation of tar. It c,ommences to go over at about 171° (340° F.), and as the temperature is raised, it is contaminated more or less with the heavier oils ; this constitutes the " Green oils." In its crude state, it contains na,phthalene, phenanthrene, creosote, &c., from which it is separated, in the first instanoe, by strs,ining, and finally, when it is well drained, by submitting it to pressure. It is then in the form of flat, irregular pieces, about in. thick, with a slight greenish colour ; exposed to the air, it changes colour, passing to a dirty-brown. The percentage of antbra,cene in this crude product is about 30. A great difficulty in its purifica tion arises from its being nearly insoluble in ordinary solvents. It may be freed from the greater part of the liquid oils by means of' a filter press. The same end is attained by pumping it up into bags, suspended over a shallow tank ; when well drained, air is pumped through, and forces out a further qua,utity of the adhering oily liquids. On a sma,11 seale, these oils are driven off by centrifugals.