If now we seek to determine the specific rotation of pure oil of turpentine from the more dilute solutions only, we get for A in the formula [a] = A + B q + C q2 values showing the following divergences:

Hence the divergence from the real value may amount, in some cases, to a whole degree, when the solutions contain more than 50 per cent. of solvent.

II. RIGHT-HANDED OIL OF TURPENTINE.

§ 31. The American oil here employed had a specific gravity of 0.91083.

For determining the rotation of the pure oil and its mixtures Wild's and Mitscherlich's instruments were used, but at the time these observations were made the experimental tubes had not been furnished with water-baths. The temperature of the liquid was ascertained at the conclusion of the measurements by a thermometer inserted into the tube.

Here also the specific rotation undergoes a slight increase with increasing dilution. The graphic representation (Fig. 16) shows that

the three points lie almost exactly in a straight line. Introducing mean value of [a] into the formula [a] = A + B q, we obtain1. Calculated from mixtures I. and II. A 14.189 B = + 0·011415

The values here obtained for A agree very closely with the

directly observed specific rotation of the oil, 14·147°.

Taking the mean of the above values for A and B, respectively,

[a]D = 14·173 +0.11782 q,

A further series of experiments with benzene as solvent led to no result, as the oil of turpentine used in preparing the mixtures was not uniform, from not all having been kept an equal length of time exposed to oxidizing influences.

III. NICOTINE (LÆVO-ROTATORY).

§ 32. The pure substance here employed was prepared from 400 grammes commercial nicotine (supplied by H. Trommsdorff, of Erfurt). To remove any small impurities of ether, alcohol, and water, the liquid was heated in a retort, whilst a stream of hydrogen passed over it, for eight hours, at a temperature of 150°, which was finally raised to 180° Cent., whereby a total distillate of 15 cubic centimetres, consisting chiefly of alcohol, passed over. The residue was then distilled in a current of hydrogen, in successive portions of 200 grammes, from a small retort heated by a sand-bath.

At 225° Cent. the nicotine, at first still retaining some water, began to pass over, but the thermometer immersed in the liquid quickly rose to 244° (corrected, 249° Cent.) when the boiling proper began. Raised into the vapour, the thermometer fell to 241·5° to 242° (corrected, 246-6° to 246.8° Cent.), which temperature remained constant during the rest of the distillation. Height of barometer, 745 millimetres. The hydrogen was admitted in a very slow stream, and no decomposition of the substance resulted. Altogether 350 grammes of pure substance, in the form of a colourless liquid, faintly tinged with yellow, were obtained. It was sealed up in glass tubes. An analysis of this nicotine, the nitrogen being determined in the gaseous form, gave the following numbers :

The preparation was submitted to further examination by titration. The nicotine was weighed in thin glass bulbs, which were then broken under water, and, after solution, tincture of litmus added,

and the liquid neutralized with a standard hydrochloric acid (containing 0.055013 gramme HCl in 1 cubic centimetre).

But one molecule nicotine, C1o H14 N2 = 161.72.

Again, in a rough titration with dilute sulphuric acid, containing 0.030369 gramme H2SO4 per cubic centimetre, 37.1 cubic centimetres served to neutralize 3-8310 grammes of substance, according to which one molecule H2SO4 (97-82) combines with 332-6 parts of nicotine; but two molecules C10 H14 N2 = 323.4.

2

The specific rotation of the nicotine was observed with the Wild's instrument, and observations were taken at three separate temperatures (10°, 20°, 30° Cent.), so as to ascertain the effect of heat. The experimental tube was provided with a water-jacket, and, measured at the mean temperature (20° Cent.), had a length of 99-923 millimetres, from which its true lengths at 10° and 30° Cent. were calculated, assuming the coefficient of expansion of the glass to be 0.0000086. The specific gravity of the nicotine, referred to that of water at 4° Cent., was also observed with the pycnometer at each separate temperature.

Another analysis, made with Mitscherlich's instrument, using a tube 49.82 millimetres long, gave a= 81.283°. The temperature of the nicotine was about 21.0°, and taking d = 1.01101, [a] = 161-38°. Accordingly the specific rotation of nicotine at 20° Cent. has been taken in what follows as

[a] = 161.55°.

(a.) Mixtures with Alcohol.

The alcohol used had a specific gravity of 0.7957 at 20° Cent. The following mixtures were observed with the Wild's instrument:

To ascertain whether the solutions were affected by keeping, mixtures I. and V. were left for a couple of days, and then examined again. The results gave for I. [a] 158.63°, and for V. [a] 145 45°, which values agree almost perfectly with those above obtained from freshly-prepared solutions.

=

=

As the table shows, the specific rotation of nicotine undergoes a pretty considerable decrease for successive additions of alcohol. Represented graphically, it takes the form of a straight line, with but small divergences either way, and consequently the values of the constants in the formula [a] Bq do not materially differ, whichever of the solutions we take.

د

=

A

Divergence from 161.55°

I. and III.

A = =: 160.90°

- 0.65°

Here even dilute solutions yield values for A, which, considering the large rotation-angle of nicotine, come pretty close to the real value.

Taking for A and B the mean of the above values, we get

[a]D

=

160.83

0.22236 q,

which gives the following interpolation values: