Nicotine mixes with water in all proportions, the more dilute solutions exhibiting a faint opalescent clouding, which necessitated a larger number of polariscopic observations. With the addition of water a considerable amount of heat is developed, so that in mixing 24 grammes nicotine with 6 grammes water, the thermometer rose from 20° to 35° Cent. The rotations were all observed with the Wild's instrument, the 99-923 millimetre tube being used for mixtures I., II., III., IV., VIII., and a short tube 49.82 millimetres in length for mixtures V., VI., and VII.

Hence it appears that the specific rotation of nicotine goes on diminishing on successive additions of water, at first very markedly, but by-and-bye at a much smaller rate. The strongly curved line

1 The specific gravity of the mixtures at first increased by the addition of water, attaining the maximum with mixture III., and then declining with each fresh addition.

(Fig. 17) forms part of a hyperbola, and it is impossible by means of the formula [a] = A + Bq + Cq, even when extended to four or

five terms, to obtain sufficient agreement with the results furnished by observation. In this case the value for pure nicotine can only be ascertained approximately by basing the calculations on the values of A for the most concentrated solutions. Thus, for mix

tures I., II., III., A = 163·17°; whereas from I., IV., VII. we get A 15300°, and from IV., V., VIII., A = 141·16°.

=

For a complete expression of the curve an equation of different form must be used, such as that calculated by Dr. Vogler, of Aachen, viz:[a] = 115·019 - 1.70607q2140-8

108-867 q + 2·5572 q2,

which affords values comparable with the results of observation as below:

For pure nicotine (2

=

=

0), the above formula gives [a]D = 161.29°, instead of the value found 161.55°; for q = 100, the value of [a] 74.13°, so that nicotine, when diluted largely with water, has its specific rotation reduced to less than one-half of the original amount.

=

IV. TARTRATE OF ETHYL (DEXTRO-ROTATORY).

§ 33. To prepare this substance, an alcoholic solution of tartaric acid was heated for some days in a water-bath along with one-tenth its volume of concentrated sulphuric acid. The mixture was then diluted plentifully with water, saturated with barium carbonate, and the filtered liquor agitated with ether. From the ethereal extract the ether was removed by distillation, and the residue in the retort heated to a temperature of 110° to 120° Cent., whilst a current of dry air was led through it so long as any traces of ether, alcohol, or aqueous vapour were observable. In this way was obtained an ethereal liquid of a pale yellow colour and syrupy consistency, which, when heated on a platinum plate, volatilized without leaving any carbonaceous residue. An attempt to distil it in vacuo was frustrated by the violence of the shocks.

As a test of its purity, 2.6079 grammes of the substance were boiled with 30 cubic centimetres of potash solution (containing

0-06336 gramme KOH per cubic centimetre), and the excess of alkali titrated with dilute hydrochloric acid, of which 37·4 cubic centimetres were equivalent to 50 cubic centimetres of the potash. For this purpose 5.6 cubic centimetres were required, so that the amount of KOH required to decompose the ether was 1·4262 grammes, corresponding to 2·6171 grammes ethyl tartrate, or 100-35 per cent. The specific gravity of the ether was 1·1989 at 20° Cent. The rotation was observed with the Mitscherlich's instrument :—

Specific gravity of alcohol employed = 0.7962 at 20° Cent.
Three solutions were examined in the Mitscherlich, with a

jacketed tube 219.90 millimetres long:

The specific rotation rises therefore slowly with successive additions of alcohol, the law of variation taking the form of a slight curve departing but little from a straight line. The formula [a] = A+Bq gives

[a]D = 8·409 + 0·018667 q.

Adopting the formula [a] = A + Bq + Cq, we get

[a]D

=

8-271 +0.024216 q - 0·000050648 q2.

Thus the values for the constant A agree very nearly with the specific rotation of tartrate of ethyl (8.31).

(b.) Mixtures with Wood-Spirit.

Specific gravity of the pure wood-spirit at 20° Cent, = 0.80915. Observations taken with the Wild's polariscope, with a jacketed tube 219.79 millimetres in length :

In this case also the increase of specific rotation experienced is small; but the rate of increase on the addition of successive quantities of wood-spirit is not uniform, being represented by a curve strongly marked at first, but afterwards much less so. Mixtures I., III., V. give the equation

[a]D

=

8.418+ 0.062466 q

0.00034786 q2,

in which constant A agrees fairly well with the specific rotation of pure ethyl tartrate. Taking only the more dilute solutions III., IV., V. into account, A = 10·25, showing at once a marked deviation from the true value, 8.31.

(c.) Mixtures with Water.

Three mixtures were prepared, of which I. and III. were examined in the Wild's polariscope, with the 219.79 millimetre tube, and II. in Mitscherlich's instrument, with the 219.90 millimetre tube: