Few manufacturers adopt these methods, unless for some special purpose. The most economical way of working is to take advantage of the preliminary distillation for the first fractionizings, and, in re-running the crude naphtha, to follow a similar plan. This entails a greater outlay in tanks for stowage, which may be economically replaced by puncheons, provided they can be kept from leaking, and from allowing the lighter products to penetrate the wond.
Solvent naphtha, or, as it is more frequently called, "solvent," is muoh used in the manufacture of indiaruhber waterproof goods, as it readily dissolves or softens indiarubbcr. It is also a solvent of resins, oils, &c., and, at one time, was largely used in the manufacture of varnishes, paints, and cements ; but for such purposes it is now almost entirely replaced by the lighter k-inds of petroleum. It is often adulterated with petroleum or shale oils. Good solvent naphtha, from English tar, has a sp. gr. of about 0'870 at 15° (60° F.), and should commence to boil at about 118° (245° F.), although it frequently requires 121° to 127° (250° to 260° F.) before any appreciable distillate goes over. Between its boiling-point and 142° (288° F.), about,70 or 80 per cent. of its bulk should pass into the receiver, and the sp. gr. of this fraction should be a trifle less than that of the original sample. The distillate collected between 142° and 160° (288° and 320° F.) should be a little heavier than the sample, and should correspond to l5 or 20 per cent. of the original bulk. The residues, when containing naphthalene, are often as high as sp. gr. 0.950, and solidify in cold weather ; otherwise the sp. gr. of the residues and fractions will not vary much from that of the solvent itself. When petroleum or shale oils are present, either as adulterants, or when the naphtha is derived from the tar of cannel coals, the sp. gr. will be 0.815. Scotch solvent goes over at lower temperatures thau the English product, and is of lighter sp. gr. If much distil at or below 118° (245° F.), petroleum oils are probably present ; this can be ascertained by the sp. gr. of the fractionized product. Scotch solvent gives 95 per cent. distillate at 160° (320° F.).
The vapours of solvent naphtha have a peculiar intoxicating power over those unaccustomed to its use ; a person thus affected rapidly recovers when taken into the open air. The effect is indicated by giddiness and hilarity, which is not followed by depression on recovery. It is rare
for the same individual to suffer more than one or two attacks. The ventilation of the buildings where it is evaporated is generally well arranged. Formerly, they were lighted, when necessary, by gas jets fixed outside the windows; now, a gool supply of air is admitted, and dilutes the vapour BO rapidly as to remove all chance of explosion. (See Indiarubber Manufactures.) Benzol, or Benzene. C6118.—This liquid was discovered by Faraday in 1825, and was named by him " bicarburet of hydrogen." In 1834, Mitscherlich obtained it by distilling benzoic acid with hydrate of lirne. It may also be procured by passing benzoic acid through a red hot tube. A mixture of one part of benzoic acid and three parts of slaked lime yields, by distilla tion, benzol in a pure state, and calcic carbonate. The mixturo should be gently aud gradually heated ; the benzol, which goes over with a little water, is separated from the latter, and distilled over a solution of caustic potash. Benzol is one of the most important principles of gas-tar ; it exists largely in the petroleums known as Rangoon tars, and in some of the petroleums of Europe, the Caspian, &c. When pure, it is a colourless mobile fluid, boiling at 81° (178° F.), and solidifying at 3° (37° F.) into a colourless crystalline mass. Its sp. gr. at 0° (32° F.) is 0.899, and at 20° (68° F.), 0.878. It has a peculiar aromatic smell, is very inflammable, and burns with a smoky flame. It is slightly soluble in water ; but dissolves freely in alcohol, ether, carbon hisulphide, and the liquids obtained by distillation from gas-tar. It is also miscible with the petroleums. It dissolves iodine, sulphur, phosphorus, fats, oils, resins, guttapercha, and indiarubher. It may be used in varnishes and in paints, as a substitute for turpentine ; but its price is too high for this at present. It removes grease spots from cloth, silk, Szc. Its volatility renders it a convenient source of illumination. The " Benzol" or " atmospheric " light is obtained by passing a current of air or hydrogen through benzol. The saturated air is distributed in tbe same way as coal-gas, and burns freely. The conditions which operate against this method of illuminating are condensation in cold weather, and the difficulty of saturating the air at low temperatures.