No stipulations as regards this are made in the British regulations, the naphtha being judged by the results of the foregoing tests. But as a guide to makers it is stated that samples which, when fractionally distilled in. the following manner, give the results indicated will as a rule be found to contain a sufficient proportion of methyl alcohol, and to be free from an excess of acetone or methyl acetate.

One hundred c.c. of the sample are to be slowly heated in a small copper flask fitted with a glass fractionating column, 7 inches high and 3/4 inch in diameter, filled to the extent of 4 inches of its height with small glass beads, provided with a thermometer placed opposite the exit tube about an inch above the beads, and connected with a spiral condenser. Not more than 10 c.c. of distillate should bo collected in the receiver when the thermometer marks a temperature of just under 65°. From 80 c.c. to 85 c.c. should pass over between 65° and 722°; and a total quantity of 97 to 98 c.c. should have distilled over before the thermometer marks 100°.

Fig. 38.   distillation apparatus.

Fig. 38. - distillation apparatus.

Used in determining the boiling range of wood-naphtha and mineral oil. A, copper flask; B, distilling tube with glass beads.

The average composition of wood naphtha submitted as suitable for denaturing purposes in the United Kingdom, and examined by the foregoing methods, may be expressed as follows: -

Per cent, by volume.

Methyl alcohol ........................................................................

77.3

Ketones, in terms of acetone ...................................................

10.2

Esters, calculated as methyl acetate ........................................

1.3

Unsaturated compounds, calculated as allyl alcohol ................

0.8

Basic ,, ,, pyridine ...........

0.2

Water .......................................................................................

12.21

102.0

1 Approximate percentage. The exact change in volume occurring when water is mixed with the other ingredients is not known with certainty.

The foregoing methods, combined with obvious modifications to meet special cases - e.g., determination of apparent alcoholic strength with the hydrometer or pyknometer; distillation; evaporation for non-volatile residue, and so on - will serve for the general analysis of wood spirit, whether intended for denaturing purposes or for use as a solvent, etc. Some further information, however, is added respecting the official methods of examination employed in France and Germany.

In France, methods based upon the same principles as the foregoing are employed for the determination of acetone and esters in wood naphtha intended for denaturing purposes. But since the specification for acetone is more rigid than in this country - the proportion being required to lie between 245 per cent. and 255 - precautions are taken to eliminate errors of measurement due to fluctuations of temperature. This is done by keeping the samples for some hours before analysis in a place maintained as nearly as possible at 15°, and by performing a "control" experiment, at the same time and under the same conditions, upon a solution of acetone in methyl alcohol, containing 25 per cent, of pure acetone. If the analysis of this shows, for instance, only 24.7 per cent, instead of the known 25.0 per cent., a correction of + 0.3 per cent. is added to the results obtained from the samples examined at the same time.

The "total impurities' of the naphtha are estimated together by an adaptation of the Rose method - namely, by shaking with chloroform and noting'the amount of increase in the volume of the chloroform (see p. 417). Twenty-five c.c. of the naphtha are mixed with 60 c.c. of water and 38 c.c. of a solution of sodium bisulphite (sp. gr. =135) containing no free sulphurous acid; this mixture is placed with 50 c.c. of chloroform in a suitable Rose tube and treated as in the description referred to. A "blank" experiment is made at the. same time with the solution of acetone in methyl alcohol mentioned above, and any resulting correction applied. From the "total impurities" as thus ascertained (referred, of course, to 100 c.c. of the sample) is deducted the percentage of esters, calculated as methyl acetate; the result gives the "real impurities," which the French stipulations require to be not lower than 2.5 per cent.

If necessary, as when the "real impurities" exceed 5 per cent., the wood spirit is examined for the presence of ethyl alcohol (see Chap. VI, p. 221).

In Germany, the directions for testing wood naphtha are as follows: -

(1) Colour

This shall not be darker than that of a solution made by dissolving 2 c.c. of iV/10-iodine in a litre of distilled water.

(2) Boiling Point

One hundred c.c. of the naphtha are placed in a short-necked copper flask of about 180-200 capacity, resting on an asbestos plate in which is cut a circular hole of 3 cm. diameter. In the neck of this flask is placed a fractionating tube 12 mm. wide and 17 cm. long, with its side tube connected to a Liebig's condenser at least 40 cm. long. In the fractionating tube, which is provided with a bulb about a centimetre below the side tube, is placed a thermometer with a scale ranging from 0° to 200°, so that its mercury reservoir is in the middle of the bulb.

The flask is heated so that the distillation proceeds at about the rate of 5 c.c. per minute. The distillate is collected in a cylinder graduated in c.c, and at 75° with a normal barometric pressure of 760 mm. at least 90 c.c. shall be collected.

If the barometer is not at 760 mm. during the distillation, 1° shall be allowed for every variation of 30 mm For example, at 770 mm., 90 c.c. shall distil at 753°.

(3) Miscibility With Water

Twenty c.c. of the wood spirit mixed with 40 c.c. of water shall give a clear, or only slightly opalescent solution.

(4) Acetone content

{a) Separation on mixing with soda solution. - Twenty c.c. of wood spirit are shaken with 40 c.c. of soda solution of sp. gr. 1.300. At least 5 c.c. of the spirit must have separated after the mixture has been allowed to stand for half an hour.

(B) Titration

One c.c. of a mixture of 10 c.c. of the wood spirit with 90 c.c. of water, is mixed with 10 c.c. of 2N-solution of sodium hydroxide. Then 50 c.c. of N/10-iodine solution are added, with continual shaking, and the mixture allowed to remain for at least three minutes. Excess of dilute sulphuric acid is then added, and the liberated iodine titrated with N/10-thiosulphate solution and starch. At least 22 c.c. of N/10-iodine solution must have been used up by the acetone. (This is equivalent to 21.3 grams of acetone per 100 c.c. of wood spirit.)

(5) Bromine Absorption

One hundred c.c. of a solution of potassium bromate and bromide (made up as described below) are acidified by the addition of 20 c.c. of dilute sulphuric acid (sp. gr. 1.290). To this mixture the wood spirit is added drop by drop from a burette so long as any colour remains on shaking. The rate of addition shall be so arranged that in one minute 10 c.c. of spirit shall have been added.

Not more than 30 c.c. of the wood spirit shall be required for the decolorisation, and not less than 20 c.c. This test must be made in full daylight, and at a temperature not exceeding 20°.