This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
In general, we may say that from 100 parts of air-dried wood are obtained by distillation 25 to 27 parts of charcoal, and 45 to 50 parts of pyroligneous liquor, or " crude wood vinegar." This last contains about 6 to 8 per cent. of acetic acid and 3 to 4 per cent. of methyl alcohol, with a little acetone and about 7 per cent. of tarry matter. In small proportions, there are present also esters (mainly methyl acetate), higher ketones, allyl alcohol, pyridine, and amines.
Various methods of obtaining purified methyl alcohol from the liquor are employed, one process being to distil it and pass the distillate through vessels containing hot milk of lime, which retains the acetic acid, the vapours of methyl alcohol and acetone passing on to be fractionated and condensed. The distillate is again rectified, then diluted, mixed with 2 or 3 per cent. of milk of lime, and very slowly distilled. The first runnings now contain much acetone, and the "tailings" include ketones of higher boiling point, whilst the middle fractions are approximately pure methyl alcohol and water.
Further purification is effected by re-distillation from lime or caustic soda, and finally from a little sulphuric acid to remove organic bases.
Oxidising agents and filtration through charcoal are other means sometimes employed in the purification. Any small quantity of acetone still remaining may be removed by passing dry chlorine into the boiling alcohol, which is then separated by fractionation from the higher-boiling chlorinated acetone, and purified from chlorine by re-distillation over lime. Bleaching powder is also used for the removal of acetone; it converts the latter into chloroform.
On a smaller scale, purification of methyl alcohol may be effected by mixing it with anhydrous calcium chloride, with which it forms a crystalline compound. This can be separated, freed from acetone by heating, and then decomposed by distillation with water.
Chemically-pure methyl alcohol is obtained by decomposing the oxalate, acetate, formate, or other methyl ester with alkalis, or with water alone. For example: The impure alcohol is digested with solid sodium hydroxide in the proportion of 150 grams of the latter to 100 c.c. of the former, and then distilled. Five hundred grams of oxalic acid are mixed with 200 c.c. of sulphuric acid, and 400 c.c. of the distilled alcohol added; the mixture is then heated on the water-bath, and the crystals of methyl oxalate which form are separated, dried by pressure between filter-paper, and hydrolysed by heating with water at 70°, The alcohol is then distilled off and dehydrated with barium oxide, calcium oxide, and anhydrous copper sulphate.1
" Absolute " methyl alcohol is best obtained by treating the strong pure spirit successively with freshly ignited lime and recently. heated potassium carbonate, leaving it in contact with the latter for some weeks, and then distilling it several times from metallic calcium.
Properties. . Pure methyl alcohol is a mobile, colourless liquid which has a faint spirituous odour, and burns with a pale blue flame. It is miscible with water in all proportions, and also with ethyl alcohol, and with ether. The boiling point has been variously given; some of the discrepancies are probably due to the presence of acetone in the spirit. The value that has been most generally accepted is 66° at normal pressure; but according to J. Gyr2 the b.p. is 6456° at 760 mm., and Fuchs3 gives it as 6506° at 710 mm., ranging up to 6800° at 790 mm. The melting point of the solidified alcohol is .949° (Ladenburg and Krugel). The specific gravity of methyl alcohol is 08100 at 0°/4°, and 079647 at 15o/15o.
Mixtures of methyl alcohol and water have nearly, but not quite, the same specific gravities as corresponding mixtures of ethyl alcohol and water. For certain proportions the difference is substantial, as will be seen from the following table: -
Sp. gr. at 15.6°/15.6°
Percentage by volume.
The greatest difference is shown by mixtures the specific gravities of which are about 0 962 to 0 963. Ethyl alcohol mixtures at these specific gravities contain 2.7 per cent. more alcohol than methyl alcohol mixtures at the same specific gravities.
Hence, although for approximate purposes the ordinary tables of (ethyl) alcoholic strength can be used with methyl alcohol mixtures, for exact work the special methyl alcohol tables should be employed. The following are published by the Bureau of Standards, Washington (Circular No. 19).
1 Dittmar and Fawsitt, Trans. Roy. Soc. Edin., 1888, 33, 509.
2 Ber., 1908, 41, 4322.
3 Zeitsch. angew. Chem., 1898, 871.