In the distillation of tar for the production of crude naphtha, the proceas ia arrested when a few drops of the distillate solidify on collection on a cool aurface. Tbe aubstance then left in tho atills contains much naphthalene and phenol. Until anthracene received commercial importance, thia reaidue was distilled for ereoaote oils only. The preaence of naphthalene in naphtha ia shown by the high sp. gr. of the residues at 160° (320°F.); on evaporating these alowly in a water bath till the bulk is reduced one-balf, and cooling, naphthalene ia obtained ; when presaed so aa to separate the adhering liquid, it will be found tolerably pure. It is sold in rolla, which are obtained by casting the melted article in moulds; in this form, it is supplied for carburetting gas, by the method known aa the albo-carbon. The further purification of naphthalene ia effected in the following way. The material ia first melted, in cloaed vessela, with a solution of cauatic soda, and well agitated. Whilst boiling, the watery vapour carries away a considerable quantity of ,naplithalene, which ahould be collected ; as the vapours cool, it is deposited almost pure. The caustic solution and naphthalene are aeparated by 000ling and compression ; after being well washed with boiling water, the latter is treated in a similar way with water acidulated with sulphuric acid. Theae operationa are repeated according to the deg,ree of putity required. It is then distilled in cast-iron retorts over a naked fire, at a temperature not much exceeding 205° (401° F.). The residue will contain much naphthaleue ; but at higher temperatures, it is contaminated with other products. The distilla tion is carried. to dryness, and the last product is added to the crude naphthalene for re-treatment.
Naphthalene crystallizes easily from saturated solutions, or by sublimation, in large ailvery white platea or acalea. It melts at 79° (171° F.) into a perfectly clear liquid, and, on cooling, solidifies into a crystalline mass. It boils at 216° (421° F.); its ap. gr. is 1'15. It is slightly volatile at ordinary temperatures. It burns with a smoky flame, being rich in carbon. It has been proposed to carburet illuminating gas with it, aa already remarked. It is insoluble in water, alkaline aolutions, and weak acids ; but is acted on by the stronger oxidizing acida. Alcohol, ether, wood naphtha, and the liquids obtained from coal-tar, dissolve it readily. With picric acid diasolved in warm alenhol, it forms a yellow solution which, on cooling, deposits beautiful yellow needles of picrate of naphthalene. This reaction ia very characteristic.
As naphthalene easily distils with the vapour of water, it may be purified by heating with wat,er, on a water bath, or by passing a current of steam into the meltedt mass ; it condenses in beautiful pure scales on the sides of the receiver, which may be made of lead, and simply inverted over the other vessel. Pure naphthalene has been used medicinally : for the production of colouring mattera, it ia not necessary to carry its purification so far. The following plan is adopted by
Calvert and Co. for producing it in a chemically rue date :—The material is treated with rectified sulphuric acid, and heated in an iron pot ; it is well stirred, and then allowed to cool and settle, when it aeparatea into two layers, one of naphthalene at the top, and a dark, tarry mass beneath. The upper portion is boiled by steam in an earthenware vessel, with frequent changes of water, until it is perfectly free from acid, adding a little weak soda to render it perfectly neutral. The naphthalene is then placed in jaoketed still, and distilled by steam-heat. The distillate ia col lected in a large receiver, and constitutes an exceedingly pure article.
The production of red, scarlet, yellow, and violet colouring matters from naphthalene has given it some importance, still its production conaiderably exceeds its demand. The heavier oils beiug leas important, manufacturers make the creoaote oila contain as much naphthalene as possible. Only a few 'naphthalene colours have received much application ; generally they lack brightness, fresh nem, and permanence. Still there is a wide field for attention to naphthalene as a source of colours; its price is considerably below that of any of the other products used for this purpose, and it is more than probable that an increased dernand for it would tend to lessen rather than enhance its cost ; it is easily purified, and its compounds are readily obtained of the necessary purity.
The general treatment of naphthalene and its derivatives for the production of colouring matters consists in direct oxidation into nitro-compounds, from which, by reducing agents, &c., as with aniline, derived compounds are obtained :— Nitro-naplithalenes.—Four nitrated naphthalenes are known : the mono-nitro is obtained by boiling powdered naphthalene, or its solution in acetic acid, with ordinary nitric acid, for half an hour ; concentrated nitric acid yields two modifications of di-nitro ; fuming nitric acid boiled with the (a) modification converts it into tri-nitro, of which there are three modifications ; two modifications of tetra-nitro are obtained by the continual boiling in nitric acid of the two previous corresponding bodies.
Naphthylamine or Amido-naphthalene. 0,0117.NE[2.—Two parts nitro-naphthalene and three of iron tornings are mixed, and acetic acid is added to cover the mixture, which should be heated so as to fuse the naphthalene. When the reduction is ended, the mass is distilled, water and acetic acid first come over, the receivers are changed, lime or soda is added to the residue, and the distillation is carried to dryness. The oily liquid which comes over solidifies, and is purified by dissolving in sulphuric acid and precipitating with ammonia, or, after adding soda in excess to the sulphate, dis tilling with steam. It crystallizes in colourless needles, melting at 50° (122° F.); it boils at 300° (572° F.) ; its hydrochloride heated with aniline to 280° (536° F.) for thirty-six hours gives naphthyl phenylamine or phenyl-amide-naphthalene.