Various other methods of detecting and estimating methyl alcohol in mixture with ethyl alcohol have been proposed. They are mostly of specialised application, and a brief reference to one or two will suffice here. Thus W. G. Toplis dries the alcohol over potassium carbonate, and then measures the volume of hydrogen evolved from a given quantity by treatment with a fragment of metallic sodium.1 The presence of methyl alcohol increases the quantity of hydrogen obtainable.

F. Wirthle detects and estimates the methyl alcohol in a mixture of the two alcohols by means of the boiling point, amount, and saponification value of the mixed iodides obtained from the sample.2

In the alcohol poisoning cases which occurred in Berlin during 1911, the proportion of methyl alcohol in the beverage taken was determined from the results of combustion analyses.3

E. Aweng confirms the presence of formaldehyde, resulting from the oxidation of methyl alcohol with permanganate, by converting it into hexamethylenetetramine with ammonia, and identifying microscopically the characteristic crystals formed by the tetramine with mercuric chloride or potassio-mercuric iodide.4

It may be noted that according to Voisenet5 minute traces of formaldehyde, detectible by the sulphuric acid and protein reaction, are formed when ethyl alcohol is oxidised by Mycoderma aceti or M. vini, or by electrolysis, as well as by oxidation with ozone, hydrogen peroxide, etc.

A scheme for the examination of liquids, animal organs, etc., in forensic cases where wood spirit is suspected has been given by Olivari.6 It is based upon the usual analytical procedure of separating bases and acids by means of their non-volatile salts, so as to obtain the neutral alcohols, etc., in the distillate.

The liquid is acidified with phosphoric acid, and the volatile acids, alcohols, etc., distilled off, leaving amines, pyridines, and other bases in the residue.

The distillate is neutralised and again distilled, the salts of the acids remaining behind, whilst neutral bodies, including alcohols, acetone, and aldehydes, distil over.

1 Amer. J. Pharm., 1918, 90, 636. 2 Chem. Zeit., 1912, 36, 700.

3 Zeitsch. Nahr. Genussm., 1912, 24, 7. . 4 Apoth. Zeit., 1912, 27, 159.

5 Compt. rend., 1910, 29, 169.

6 Arch. Farmacol. Sperim., 1913, 15, 83; Chem. Zentr., 1913, i, 1780.

Aldehydes are ' fixed ' by treatment with metaphenylene-diamine hydrochloride (see Chap. XI, Girard and Cuniasse's method for estimation of higher alcohols). On again distilling, the methyl alcohol is obtained in the distillate, together with any acetone present in the wood spirit, and the two can now be estimated by any convenient process.

V. Methyl alcohol and formaldehyde - When these two substances occur together in aqueous solution they may be estimated by one or other of the following methods: -

(1). If only very small quantities of the two are in question, the solution is mixed with ethyl alcohol in such proportion as to give 10 per cent. of alcohol, as described for Deniges's method of estimating methyl alcohol (p. 183).

(a). In one quantity of 5 c.c. the formaldehyde is determined by colorimetric comparison with a standard solution of formaldehyde, proceeding just as described for methyl alcohol, but omitting the oxidation with permanganate, and using 3 c.c. of water instead of the same volume of permanganate and oxalic acid.

(b). At the same time, the colour produced is matched by comparison with a standard solution of methyl alcohol, oxidised precisely as required in the estimation of this alcohol.

(c). In another 5 c.c. of the prepared sample the alcohol is oxidised and the resulting total colour with Schiff's reagent estimated in terms of methyl alcohol, as described on p. 184. Deducting the result of (b) from that of (c) gives the proportion of methyl alcohol.

(2). With larger proportions of formaldehyde the quantity of this ingredient may be determined by one of the well-known methods - e.g., by oxidation with iodine in alkaline solution, and determining the excess of iodine, after acidifying, with sodium thio-sulphate. The methyl alcohol is estimated by Deniges's or other convenient method after removing the formaldehyde by distillation with potassium cyanide, twice repeated.

(3). When still larger proportions of formaldehyde are present, as in the commercial product "formalin," the process described by Lockemann and Croner1 may be used. On adding hydroxylamine hydrochloride to formaldehyde, hydrochloric acid is liberated according to the equation: solution free alkali is produced, and the estimation may be made by titrating this: -

CH1O + NH1 .OH.HC1 = CH1.NOH + H1O + HC1.

The acid can be titrated, and the formaldehyde thus estimated. Methyl orange is used as the indicator.

Alternatively, by adding sodium sulphite to the formaldehyde

1 Zeitsch. anal. Chem., 1915, 54, 11.

CH1O + Na2SO3 + H1O = CH1(OH)SO3Na + NaOH.

In this case rosolic acid is used as the indicator.

The methyl alcohol is determined by oxidising the mixture with alkaline permanganate and calculating the alcohol from the quantity of permanganate reduced, after deducting the quantity. used up by the formaldehyde. The 40 per cent. solution (formalin) of formaldehyde is diluted to 100 times its bulk with water, and 5 c.c. of this solution are mixed in a flask with 75 c.c. of water and 25 c.c. of N/2 -permanganate, containing 15.82 grams of KMnO4 and 40 grams of NaOH per litre. After being heated on the steam bath for 20 minutes, the mixture is treated with an excess of N/2-oxalic acid solution (31.51 grams of the crystallised acid with 75 c.c. of strong sulphuric acid, per litre). The excess of oxalic acid is then determined by titration with acid permanganate solution of N/2 -strength, containing 40 grams of crystallised phosphoric acid per litre. Each c.c. of the alkaline N/2-permanganate used up oxidises 0.00375 gram of formaldehyde or 0.00267 gram of methyl alcohol, and the quantity of formaldehyde having been already determined the corresponding amount of permanganate can be calculated and deducted, the remainder being then calculated to methyl alcohol.