Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/205

Rh METHYL 195 is never made synthetically, but simply extracted from wood-spirit, a commercial substance which is produced industrially in the dry distillation of wood. The wood- spirit is contained in the aqueous portion of the tar pro duced in this operation, along with acetic acid. To recover both, the tar-water is neutralized with lime and distilled, when the acetate remains, while the spirit distils over, along with a deal of Avater, which, however, is easily removed, as far as necessary, by redistillation and rejection of the less volatile parts. The &quot; crude &quot; wood-spirit, as thus obtained, is not unlike in its general properties to ordinary spirit of wine, from which, however, it is easily distinguished by its abominable smell. The ordinary commercial article, besides a variable percentage of water, contains from 35 to 80 per cent, of methyl-alcohol ; the rest consists chiefly of acetone, but besides includes dimethyl-acetal, C.&amp;gt;H 4 (OCH, 5 ) 2, acetate of methyl, and numerous other minor components. In Great Britain large quantities of wood-spirit are used for the making of methylated spirit, a mixture of ordinary spirit of wine with one-ninth of its volume of wood-spirit, which is allowed to be sold duty free for the preparation of varnishes, and for other industrial purposes. In former times, here as elsewhere, wood-spirit itself used to be employed as a cheap substitute for spiritus vini ; but this is no longer so, since the aniline-colour industry has created a large demand for pure methyl-alcohol. Hence in some Continental works the wood-spirit, instead of being sent out as such, is being worked up for its components, by the following sequence of operations : (1) dehydration by lime ; (2) heating, under an inverted condenser, with caustic soda, to convert the acetate into hydrate of methyl ; (3) destruction of the bad smells by mild oxidation ; (4) distillation in a kind of Coffey s still, whereby it is split up into approximately pure alcohol, acetone, and &quot;tails.&quot; The new industry led to the invention of the following technical methods for the determination, in a given spirit, of the percentages of real methyl-alcohol and of acetone. The alcohol is determined by saturating 5 c.c. of the spirit with hydriodic acid (volatilization of alcohol and iodide of methyl being avoided by means of a cold-water bath and an inverted condenser), and the product poured into water. Iodide of methyl separates out as a heavy oil, which is measured as it is. According to direct trials 5 c.c. of pure methyl-alcohol yields 7 45 c.c. of crude iodide (Krell, Kramer and Grodzky). For the determination of the acetone the following reagents are required (Kramer) : (1) a solution of iodine, prepared by dissolv ing I 2 = 254 grammes of iodine, by means of (say) 500 grammes of iodide of potassium, in water, and diluting to 1 litre ; (2) a solution of caustic soda containing twice (NaOH) grammes per litre ; (3) alcohol-free ether. Ten c.c. of the soda are placed in a gra duated cylinder and mixed intimately, first with 1 c.c. of the spirit, then with 5 c.c. of the iodine solution. lodoform separates out (if acetone is present) in minute yellow crystal plates ; this product is &quot;shaken out &quot; by means of 10 c.c. of ether, and determined by evaporating an aliquot part of the ethereal layer in a tared watch- glass to dryness and weighing the residue. C 3 H t( yields CHI 3 ; hence 1 part of iodoform indicates 28 parts of acetone. The formula of methyl-alcohol and its true chemical character were correctly ascertained by Dumas and Peligot as early as 1834 ; yet pure methyl-alcohol may be said to have been an unknown substance until 1852, when Wohler taught us to prepare it, by first extracting the CH 3 of the CH 3 OH in the wood-spirit as oxalate of methyl, and then decomposing the (purified) oxalate with water. The most convenient raw material to use nowadays is the commercial &quot;pure&quot; alcohol; if wood-spirit is employed it had better first be purified by distillation over caustic soda (vide supra). The formation of the oxalate then is best effected (according to Alexander Watt) as follows : 500 grammes of oxalic acid crystals are mixed with 200 c.c. of oil of vitriol ; then 500 c.c. of the spirit are added, the whole kept for a time at 80 C., and then allowed to stand cold for twenty-four hours. The large crop of oxalate crystals partly (CH 3 ) 2 C 2 4, partly CH 3. H. C 2 4 is separated from the liquor by pressure and subse quent drying over vitriol, and then decomposed by distillation with water. The aqueous alcohol thus obtained is dehydrated by the well- known methods used in the preparation of ordinary absolute alcohol. According to Kramer, a purer preparation than Wohler s is obtained by extracting the methyl as fonniate instead of as oxalate, which is easily effected by digesting the wood-spirit with a formic acid of 1 22 specific gravity, and purifying the formic ether by fractional distillation. This ether Loils at 32, the oxalate at 161 r C., hence a proper combination of the two methods should be infinitely superior to either. What now follows must, in general, be understood to refer to Wohler s preparation. Pure methyl-alcohol is a colourless liquid similar in its general properties, in its behaviour to other chemically inert liquids, and in its action as a solvent to ordinary absolute alcohol, from which, however, it differs by the entire absence from it of all spirituous odour. A pre paration which smells of wood-spirit may be condemned at once as impure. According to H. Kopp, its specific gravity is S142 at C. and 7997 at 16 4. If the volume at t be V, then (from to 61) The boiling point is 64 0- 6 to 65 2. The tension-curve was determined by Regnault and by Landolt ; but the results of the two observers do not agree except (approximately) at P = 760 mm. Methyl-alcohol has quite a characteristic tendency to &quot; bump &quot; badly on distillation, which, however, can be prevented by addition of a small fragment of tin- sodium, which produces a feeble but sufficient current of hydrogen. Its specific heat is 67 1 3 ; latent heat of vapour, 26 4 ; combustion heat, 5307 per unit weight (Favre and Silbermann). The refractive index for the D (sodium) ray is 1 3379 0013 for 10 T 5 C. (Dale and Gladstone). Methyl-alcohol mixes with water in all proportions with contraction. Since Wohler s discovery a table for the specific gravities of aqueous methyl-alcohols has been constructed experimentally by A. Dupre ; but unfortunately his alcohol boiled at 58 7, and con sequently must have been something different from what generally goes by this name. In its chemical reactions methyl-alcohol, CH 3. OH, is very similar to ordinary (ethyl) alcohol, C 2 H 5. OH, and consequently, in the same sense as the latter, analogous to water, H. OH. Thus, for instance, metallic sodium and potassium dissolve in either alcohol with evolution of hydrogen and formation of ethylates or methylates of the alkali metals. Example The two methylates crystallize from the solution with crystal-alcohol, which can be driven off in an atmosphere of hydrogen by heat, without decomposition of the salts themselves. Water at once decomposes them into caustic alkali and alcohol, CH 3. ONa + H. OH = NaOH + CH 3 OH. Yet the reverse reaction takes place when the alcohol is treated with a large excess of caustic soda. The action of acids on methyl-alcohol is in general quite analogous to that on, for instance, caustic soda, with this important difference, however, that what in the case of NaHO goes on so readily in aqueous solutions with CH 3. OH succeeds only under circumstances precluding the accumulation of water. In these circumstances we have, for instance, (1) C1H + OH. CH 3 = H 2 + Cl. CH 3 ; (2) (C 2 H 3 2 )H + OH. CH 3 - H 2 + C 2 H 3 2. CH 3 ; Acetic acid. Acetic ether and so on with all monobasic acids. A dibasic acid XHH may act as (X)H, or as (XH). H ; thus, for instance, (3) (C 2 4 H)HTOH. CH 3 = H 2 + C 2 4. HCH 3 ; Oxalic acid. Methyl oxalic acid. (4) (C 2 4 )H 2 + 20H. CH 3 = 2H.,0 + C 2 4. (CH 3 ) 2 ; Methyl oxalate.