Purification of Anthracene.—For final purification, anthracene is submitted to distillation, and the product coming over between 332° and 319° (630° and 660° F.) is collected. The distillate will contain a little anthracene before it reaches these temperatures ; hut as the object is to obtain the article free from impurities, it is better to collect the distillate between temperatures which will allow tbe maximum quantity to come over. In the distillation of anthracene, there is always formed a large quantity of tarry matter, resulting from the decomposition of a portion of the anthracene, so that as little heat as possible should be used. The hest way of conducting this operation is to place the partially purified anthracene in an iron retort, set in blickwork, and heated by a furnace immediately underneath; as soon as the contents boil, a current of deoxidized air or steam is blowu through ; this carries the anthraceue into a closed chamber, where it con denses, Preference is given to steam : air carries the sublimate over dry, but is liable to oxidize it. Tbe sublimate is dissolved in recently-drawn naphtha, boiling at 121°-149° (250°-300° F.); the naphtha is saturated at the boiling-point, and, on cooling, deposits the anthracene in crystals, which are drained, strongly pressed, dissolved in alcohol, and recrystallized. They still possess a slight yellow colour, which it seems is not entirely removed by redissolving and crystallizing; but may be removed hy washing with ether, or carbon bisulphide, or by carefully crystallizing from benzol with exposure to light. The pure crystals possess a fine blue fluorescence. Pure anthracene solidifies at 210°-215° (410°-420° F.); boils at 360° (680° F.); and evaporates slig/atly at its point of fusion ; its vapours have a disagreeable odour, and are irritating if inhaled. Alcohol and ether
dissolve it sparingly ; benzol, readily, especially when heated; in water, it is insoluble. It has been obtained synthetically ; and although the methods for obtaining it in this way are, at present, of scientific rather than of practical importanoe, still the high price of the pure article, and the demand for its derived colouring matters, are sufficient inducements for research in this direction. The present price of the crude article containing 60 per cent. anthracene is about 1501. a ton ; the value of the pure article would bo about 15/. a lb. Improvements in the manufacture of this substance may be directed towards the prevention of loss in subliming or distilling ; it might be well to try the effect of the superheated vapours of benzol or naphtha injected into the retorts, instead of steam, for the anthraceno might be much more economically sublimed, even if a little loss of an expensive solvent were incurred. A difficulty would be met with in the condensing; but it doeS not appear insurmountable.
Instead of the naphtha process, the article is sometimes purified at once by distillation with lime and caustic potash. There is a difference of opinion as to the merits of this process, as the coking which takes place with steam, even at high pressure, entails a great loss in working. Experience generally is in favour of the distillation with potash, and it is not improbable that, when this process has been unsuccessful, there has been a want of proper precaution in heating the retorts, for as a rule, bodies volatilizing at very high temperatures require much more care, and whilst superheated steam may admit of easier adjustment, it is probable that extra care with the potash process would be compensated for in the yield.