Shale naphtha is a complex mixture of hydrocarbons belonging to the two series, paraffins and olefines, the latter forming about 60 per cent. of the naphtha. There have been found hexene, CH12; heptene, C, H14; octene, Cg H16; and nonene, C, H18 among the olefines: hexane, CH14; heptane, C, H16; octane, CH18; and nonane, C, H20 among the paraffins; but other members of these two series are present.

Shale naphtha is largely used as a substitute for turpentine, and on the whole is a good material for the purpose. It is distinguished from both turpentine and rosin spirit by its much lower gravity, its flash point, its indefinite boiling point, the low temperatures at which it distils, by not being affected by sulphuric acid, and by not being completely distilled in a current of steam as is turpentine.

BENZOLINE, Benzine, or Petroleum Spirit.-When the petroleum obtained from the oil wells of North America is subjected to distillation three products are obtained-viz., "naphtha," "kerosine," and "residuum.”

The "naphtha" is refined by treating with sulphuric acid, then with caustic soda, and distilling, when three products are obtained-viz., "gasoline," "benzoline," and "naphtha." The first gasoline is a very light product, having a specific gravity varying from 0.680 to 0.700, and is used only for special purposes. The other two products are sold indiscriminately under the names of "benzoline," "benzine," and "petroleum spirit." These products vary much in quality. They are water-white, very limpid liquids having a specific gravity ranging from 0·730 to 0.760, but heavier samples are met with.

In its general properties benzoline resembles the shale naphthas; what is generally sold under that name has a specific gravity of about 0.730; it flashes and takes fire at the ordinary temperature; it begins to distil at about 65° C., and is usually completely volatilised at 150° C.

A sample tested by the author gave the following results :—

This is a light sample; usually only about 50 per cent. distils over below 100° C.; and some samples do not contain any portion distilling below 100° C.

In its general features, chemical composition, and uses, petroleum spirit resembles shale spirit; it contains, however, a larger proportion of the paraffin hydrocarbons.

Certain substances are met with in the market, and sold as "turpentine substitute," and other fancy names more or less resembling turpentine, which are petroleum and paraffin products rather heavier than naphtha. A sample of such examined by the author had a specific gravity of 0.7913, a flash point of 36° C. (97° F.), and began to distil at 156° C., the rate of distillation being as follows:

:

No further portion was distilled.

Such products are rather slow in drying, but they are better substitutes than petroleum spirit, because they are less inflammable, and there is, therefore, less risk of fire in using them. They do not oxidise or leave any residue on evaporation.

COAL-TAR NAPHTHA.-Coal-tar naphtha is not much used in paint-making; but in the preparation of varnishes it finds some use. It is one of the products obtained during the distillation of coal-tar. In this operation several products are obtained, the proportion and nature of which depends partly upon the composition of the tar and partly upon the manner in which it is distilled. Among the products is a light oil or spirit of a dark brown colour, known as "naphtha" or "light oil;" in specific gravity it ranges from 0.840 to 0.940. Its odour is characteristic, but somewhat disagreeable. Its composition is complex, containing hydrocarbons of the paraffin and olefine series in small quantities, but its characteristic constituents are hydrocarbons of the benzene series, such as benzene, Ce He; toluene, C, Hg; xylene, Cg H10; cumene, C, H12; durene, C10 H14; besides these it contains ammonia, aniline, toluidine, and other nitrogenous bodies; alcohol, phenol, acetic acid, and sulphur compounds. It is purified by re-distillation, when what is called “ naphtha" is obtained; this is further purified by treatment with sulphuric acid, which removes all the basic bodies, the hydrocarbons of the olefine and crotonylene series, and the higher members of the benzene series. After separating the acid from

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8

once run

the semi-purified naphtha, the latter is treated wtih caustic lime or caustic soda, which removes all the oxygen and sulphur compounds; finally, the naphtha is well washed with water, and is then ready to be finally purified by a re-distillation.

Once run naphtha has a specific gravity of 0.886 to 0.893, and is the raw material for the preparation of 90 per cent. benzol, "50/90 per cent. benzol," 30 per cent. benzol, solvent naphtha, and burning naphtha, as the commercial products are named.

The benzols are light products used in the manufacture of aniline dyes. Burning naphtha, which has a specific gravity of about 0-880 to 0.887, is sold for burning in out-door lamps, especially costermongers' lamps, although it has of late been largely displaced by the petroleum oils for this purpose.

Solvent or coal-tar naphtha is largely used in the india-rubber industry, and for making varnish. It is a water-white liquid, having a peculiar and characteristic odour of coal-tar hydrocarbons; in specific gravity it varies somewhat, the usual range being between 0.865 to 0.877. On being subjected to distillation, it gives from 8 to 30 per cent. of distillate below 130° C., while as a rule 90 per cent. distils over below 160° C. It burns with a very smoky flame, and is very inflammable, the flash point being about 120° F. It is miscible with alcohol, ether, turpentine, petroleum spirit, shale naphtha, and other similar solvents, while it is a good solvent for oils, fats, resins, and is almost the only solvent for coal-tar pitch, and other pitches.

In composition it is very complex, but it consists chiefly of the three isomeric, para-, meta-, and ortho-xylenes, Cg H10, cumenes, small quantities of paraffins and olefines, and occasionally traces of naphthalene. Sulphuric acid has little or no action on coaltar naphtha, but nitric acid has a powerful action, and transforms the coal-tar hydrocarbons into the nitro derivatives, nitroxylenes, Cg H, NO2; nitro-cumenes, &c. Hydrochloric acid, caustic soda, and caustic potash have no action on it.

It is used in making cheap quick-drying varnishes, rosin being the usual substance added to give the requisite coat; it is more volatile than turpentine, although it does not leave any residue behind it.

Commercial coal-tar naphtha is occasionally adulterated with petroleum or shale spirit, or with petroleum or paraffin burning oils; in every case the specific gravity and flash points are reduced. The addition of the petroleum and shale spirits causes it to distil at lower temperatures and a little more regularly, while the burning oils raise the distillation temperatures rather considerably.

Such additions may also be detected by treating the suspected sample with a well-cooled mixture of sulphuric and nitric acids, which converts all the coal-tar hydrocarbons into nitro-compounds, while the paraffin or petroleum oils are unaffected; if now water is added, the nitro bodies, being heavy, sink to the bottom, while the petroleum hydrocarbons being light rise to the top, and may be collected and measured. It should be pointed out that finding a small amount of such unchanged hydrocarbons does not necessarily indicate adulteration, as coal-tar naphtha naturally contains small quantities of paraflin hydrocarbons.

The best method of examining coal-tar naphtha for its quality is by distillation. The method commonly used is the following:-100 cc. of the naphtha is measured by means of an accurate glass measure into a tubulated retort of 200 cc. capacity; through the tubulure is inserted a thermometer, the bulb of which reaches within of an inch of the bottom of the retort. The beak of the retort is connected with a long Liebig's condenser, and the distillation carried on by means of a Bunsen burner. It is best to insert the bulb of the retort into a deep sand bath, so that if the retort should crack, the naphtha would flow into and be absorbed by the sand, and no disastrous results ensue. The temperature at which the first drop flows from the end of the condenser is noted; with naphtha this occurs at about 110° C. Then the rate of distillation is noted; at 120° C. about 20 per cent. will come over, at 130° C. about 60 per cent., at 140° C. about 72 per cent., and 90 per cent. usually comes over below 150° C. Or, instead of taking the temperatures, as in the above example, and noting the quantity distilled at them, the temperature at which each successive 10 cc., or 10 per cent., comes over may be noted; the results will then be somewhat as follows:10 per cent. at about 128° C., 20 per cent. at 130° C., 30 at 132° C., 40 per cent. at 135° C., 50 per cent. at 137° C., 60 per cent. at 140° C., 70 per cent. at 145° C., 80 per cent. at 148° C., 90 per cent. at 158° C. Addition of petroleum or shale spirits increases the proportion distilled at the different temperatures, while petroleum or paraffin burning oils decreases the proportion considerably. Sometimes the makers take out the lower benzene hydrocarbons and thus reduce the value of the coal-tar naphtha for the particular purpose; in such case, the temperature of distillation will be increased.

per cent.

The following table shows, in a comparative form, the properties of turpentine, rosin spirit, shale and petroleum spirits, and coal-tar naphtha:

METHYLATED SPIRIT-Methylated spirit is a very useful article in the preparation of varnishes and enamel paints. It consists essentially of a mixture of two bodies, methyl alcohol and ethyl alcohol; but in the ordinary commercial qualities there are usually small traces of other bodies, some of an ethereal character, others of an acid character.

The alcohols are a very large and important group of chemical compounds, many of them finding extensive application in the various chemical arts. The type of the group is ethyl alcohol, C, H, OH, the body usually understood by the term alcohol when used by itself. It is also known as spirit of wine, for to it is due the intoxicating effect of wines, spirits, beers, and all beverages which have undergone fermentation.

Pure ethyl alcohol is a colourless, very limpid liquid, having a pleasant odour and a hot burning taste. It is very volatile when exposed to the air, passing off completely and leaving no residue behind. It boils at 78°.5 C. (173° F.) and distils over completely and unchanged at that temperature. It is only solidified when subjected to the very low temperature of- 130° C. The specific gravity of pure alcohol at 15°5 C. (60° F.) is 0.7935; but it has such an affinity for water that the preparation of a sample absolutely free from water is exceedingly difficult, so that the gravity given above may not be quite correct, but the error, if there is any, is small. Alcohol mixes with water in all proportions; if the two bodies are fairly pure the proportion of alcohol