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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
may be ascertained by simply determining the specific gravity (see table on p. 419). It mixes with ether, chloroform, turpentine, carbon bisulphide, and benzol, but not with petroleum products. It dissolves fatty acids and castor oil readily, but it has only a slight solvent action on the other fatty oils. It dissolves rosin and a few other resins, such as, shellac, sandarac, mastic, more or less completely; but it will not dissolve the hard copals, animi and kauri. It is a powerful solvent for coal-tar dyes, and other bodies.
When subjected to the action of oxidising agents it is first transformed into aldehyde, CH,COH, and then, finally, into acetic acid, C H2COOH.
It is obtained as a product of the fermentation of sugar; this body, which is present in grapes, malt, and fruits of all kinds, if kept under conditions which cause it to enter into fermentations loses carbonic acid and water, while alcohol is formed in fair proportions; this passes into the water in which the process is conducted and from which it is separated by distillation, and redistillation with the aid of quicklime.
The alcohol ordinarily met with in commerce is known as “rectified spirit of wine;” this has a specific gravity of 0.838, and contains 86 per cent. of real alcohol; what is known as "proof spirit ” has a specific gravity of 0-926, and contains 49 per cent. of real alcohol.
Alcohol alone is not used in the preparation of varnishes as the high rate of duty levied by the Excise Authorities prohibits its use for this purpose.
Methyl alcohol is a homologue of ethyl alcohol; and has the composition indicated by the formula CH, O H. When pure it is a colourless liquid, very mobile and volatile, which has a fragrant spirituous odour, and boils at 55° C. Its specific gravity at 15°.5 C. (60° F.) is 0.8021, but authorities vary a little on this point. It is miscible in all proportions with water, from which it is not easily separated; it also mixes freely with alcohol, ether, turpentine, &c., and possesses great solvent properties for resins, &c.
When subjected to the action of oxidising agents it is first changed into formaldehyde, HOOH, then into formic acid, HCOOH.
Methyl alcohol is obtained in large quantity in the dry distillation of wood. The wood is placed in iron stills or retorts in suitable furnaces, when there come over gaseous vapours, which condense, partly into an aqueous layer, and partly into a tarry mass. The aqueous layer, which has an exceedingly complex composition, contains acid, alcoholic, phenolic, ethereal and
other compounds. It is separated from the tar, treated with slaked lime, and then subjected to heat; crude wood-spirit distils over, while impure acetate of lime is left behind in the still.
The spirit is very impure, and is further treated by redistilling for quicklime, then treating with sulphuric acid (which removes ammonia and methylamine) and, finally, redistilled with lime.
Crude wood-spirit, as obtained by the above process, is a liquid of complex composition, containing about 95 per cent. of methyl alcohol in the best qualities, although some samples do not contain more than 40 or 50
cent. The following bodies are found in wood-spirit, or wood-naphtha as it is sometimes called:Methyl alcohol, CH2OH; acetone (CH3)2 C 0, sp. gr. 0·792, b. p. 56o.5 C.; allyl alcohol, C, H, OH, sp. gr. 0-8604, b. p. 96° 5 C.; furfurol, ketones, c.
The odour of wood-naphtha is characteristic and somewhat unpleasant. It is due entirely to the impurities which are present in the spirit. Its taste, for the same reason, is extremely nauseous; hence the use of wood-naphtha in making methylated spirit.
Wood-naphtha is used for dissolving gums and resins in varnish making, and it is worth noting that many of the gums are more freely soluble in the crude wood-naphtha than they are in the pure methyl alcohol. The cause of this increased solvent power of the crude spirit must reside in the ethereal impurities it contains, many of which dissolve resins more freely than does methyl alcohol.
The following reactions serve to distinguish wood-spirit from pure methyl alcohol:-caustic soda gives a brown colour, sulphuric acid a red colour, which increases in depth on heating; mercurous nitrate gives a grey precipitate of mercury.
Methylated spirit is a mixture of 90 parts of rectified spirit of wine with 10 parts of wood-spirit, and this mixture is permitted by the Excise authorities to be sold, under special regulations, for manufacturing purposes free of duty, the addition of the wood-spirit rendering the spirit undrinkable. Of late, however, owing to improvements in the manufacture of the wood-naphtha, much of the nauseous taste is removed, and the methylated spirit now made is not so undrinkable. On this account the Excise authorities have recently compelled the addition of } per cent. of petroleum oil to the methylated spirit, with the object of rendering it still more undrinkable, but the use of the original spirit is still by special permit allowed.
The methylated spirit is usually sold at a strength of “64 over proof," and has a specific gravity of 0.821. It contains 90 per
cent. of real alcohol. The meaning of the term “64 over proof” is that when 100 volumes of this spirit is mixed with 64 volumes of water, there is obtained “proof spirit,” which is a spirit of such a strength that when mixed with gunpowder it will not set fire to the powder when a light is put to it. The term “proof spirit” is very vague, and should be done away with. It would be better to sell the spirit according to the actual quantity of alcohol it contains.
The strength of methylated spirit may be fairly accurately estimated from its specific gravity. Tables have been constructed showing the quantity of alcohol contained in spirit of different gravities. Space cannot be spared in this book for the reproduction of those tables, but the following table contains some information on this point which may be of use :
* Rectified spirit of wine. + Proof spirit. Methylated spirit generally has an acid reaction, due to the presence of small quantities of acetic acid and aldehyde; besides these, it contains traces of higher alcohols (amyl alcohol, propyl alcohol), oily and resinous bodies, ethereal compounds, and water.
Methylated spirit is used in making varnishes from shellac, sandarac, rosin, mastic, dammar, and other resins; such varnishes are very quick in drying owing to the volatility of the methylated spirit. It is also used in the preparation of enamel paints.
The quality of methylated spirit may be ascertained by distilling 100 c.c., when nearly all should be distilled below 100° C., the great bulk passing over between 80° and 90° C. The specific gravity is also a good indication of the quality, as shown in the table given above. In making any determination of the specific
gravity particular attention must be paid to the temperature at which it is determined, as small variations of temperature cause considerable alteration in the gravity; the standard temperature is 15°•5 C. (60° F.). The actual determination may be made by means of an hydrometer—either the glass one; or the metal one, known as Sikes' hydrometer, which is used by the Excise authorities; or the specific gravity bottle may be used.
Finish or methylated finish is methylated spirit containing about 3 oz. of rosin to the gallon. For some purposes this
be used in the place of methylated spirit, as the Excise do not place so many restrictions on its sale. It may be distinguished from the pure spirit by its giving a very copious white precipitate when water is added to it.
On the Continent distilled animal or “Dippels” oil is used for the denaturing (or rendering undrinkable) of alcohol; the use of this material has not been adopted in this country.
The flash point of methylated spirit varies from 57° to 60° F.