ART. IV.-Effect of Temperature on the Power of Solutions of Quinine to rotate Polarized Light. The corrections to be applied for the same. Suggestions regarding the preparation to be used when Quinine is employed as a Medicine; by JOHN C. DRAPER, Professor of Natural History, College of the City of New York.

IN an admirable article on "The Action of the Solution of certain Substances on Polarized Light," by O. Hesse, in the Annalen der Chemie for 1875, the writer after dealing at length with the varying action of the alkaloids on a beam of polarized light says: "If we now take into consideration the fact that transparent bodies, as water and alcohol, are able, under the influence of electro-magnetism to deflect the plane of polarized light, although this property does not otherwise belong to them; and that the optical powers of a substance can be influenced by mere mechanical means, as Scheibler has proved in certain kinds of glass; we must admit, that 'There is no real relation between the rotating power of a substance and its molecules.'" He then adds, "The rotating power of a substance is simply the result of the variable action of its factors, viz: the arrangement of the molecules as regards the volume, the solvent, the temperature, the concentration, the chemical combination, the dissociation and other things."

The importance of utilizing the rotation power of quinine for the practical purposes of analysis has induced me to endeavor to determine, as far as possible, the corrections to be applied for the variations in question, and especially for those dependent on temperature. Concerning this, A. Bouchardat says, "variation in temperature causes variation in the rotation power of quinine." In the paper mentioned above, O. Hesse says, "in the case of Thebaine and Quinine the rotation diminishes under an increase of temperature;" but he afterward adds, "I found that the variation between 15° C. and 25° C. was insignificant."

In my experiments the polariscope employed belonged to my friend, Dr. R. A. Witthaus. It was made by Laurent, of Paris, and read by verniers to two minutes. The tube was of glass 220 millimeters in length, with a lateral aperture near the center, through which a thermometer was introduced for the determination of temperature. Around this tube I placed a water jacket, the temperature of which was easily raised to and kept at any required degree, by the injection of steam through a pipe which passed to the bottom of the jacket. Having satisfied myself by a series of experiments that extreme variations of temperature in the water of the jacket, or bath, did not produce

any appreciable effect upon the indications of the instrument itself, I proceeded to the determination of the rotation power of the purest sample of quinine I could procure.

Bearing in mind the statement quoted above, that the concentration, solvent and chemical combination have their influence on the amount of rotation, I assumed specific conditions for the preparation of the experimental solutions which might be easily reproduced. They were, 1st, the use of the uncombined alkaloid quinine, carefully dried over strong sulphuric acid, 2d, ninety-seven per cent alcohol as the solvent and a concentration proportion of one gram of quinine, to fifty cubic centimeters of the alcoholic solution. For the sake of convenience the factors required in calculating the results are presented in the following tabular arrangement, viz:

v. volume of 97 p. c. alcoholic solution=50 cubic centimeters. p. weight of quinine = 1 gram.

A. length of tube

-220 millimeters.

a angle of rotation observed with sodium flame.

αχυ

The formula being [a]j= × 100 and the average of 200

Χρ

observations on four solutions at a temperature of 25° C. being a=-6-789° we have

Raising the temperature to 47° C. the average of 200 observations on the same solutions as before was a=-6·245° from which by the formula we have

The difference of temperature in (1) and (2) being 22° C. and the difference in the angle of rotation 12 37°, it follows that 1° C. 562° difference.

That is, in a solution of quinine of the strength in question, viz: 20 milligrams of alkaloid to one cubic centimeter of alcoholic solution, for each additional degree Centigrade of temperature the angle of rotation diminishes 562 of a degree.

To ensure the correctness of these figures I caused my assistant, Mr. Ivan Sickels, also to carry out a series of experiments, and the result of seven hundred observations at temperatures between 25° C. and 47° C. gave figures which only differed in the third decimal place. We are therefore justified in employing the correction in question for values in the vicinity of 25°

C. which closely approaches the temperature at which such observations are made in actual practical work.

Effect of variation in the Proportion of Alcohol in the Solution.Hesse having shown that the strength of the alcohol has a marked effect on the rotating power of quinine, it followed that perhaps variation in the proportion of quinine dissolved in a given specimen of alcohol would also give variation in the power of rotation. In the examination of this problem I employed a freshly prepared solution of one gram of undried quinine in 50 cubic centimeters of 97 per cent alcohol. The average of 100 readings of the angle of rotation at various temperatures from 20° C. to 50° C. was

(3) α=-6·05° at 35° C.

To the above 50 cubic centimeter solution 50 cubic centimeters of the same alcohol were added, forming a solution of half the strength of the first solution. The average of 100 readings at similar temperatures was

(4) a=-2·61° at 36° C.

To this second solution an equal volume of alcohol viz: 100 c. c. was added, giving a solution of one quarter the strength of the first. The average of 100 similar readings was

(5) a=-1·27° at 36° C.

In the first solution (3) p=1 and v= 50
In the second solution (4) p=1 and v=100
In the third solution (5) p:

Χρ

=

and v=200

X100 we have

-6.05°×50

αχυ

For (3) [a]j=

X100=-137.50° at 35° C.

220×1

From the above experiments we perceive that the effect of a dilution by alcohol of the solution of quinine is to lessen its power of rotation, and as far as the experiments have been conducted this effect is more marked in the first degree of dilution than in the second.

The repetition of these experiments by Dr. R. A. Witthaus and Mr. Sickels, on a similar series of solutions made with the same alcohol and an undried specimen of quinine, gave the following averages of many hundred readings.

In the 1st solution (6) p=1∙∙v=50••λ=220 •• a=-5′58° at 29° C. In the 2d solution (7) p=1..v=100··λ=220 ··a=-2·40° at 31° C. In the 3d solution (8) p=1..v=200 ··λ=220 ··a=-1·17° at 35° C.

Here again we perceive that the effect of dilution is to diminish the power of rotation, and to about the same extent and in the same manner as in my series of observations. It is therefore evident, that to secure results suitable for a reliable comparison, the solutions of quinine employed should be as nearly as possible of the same strength. The proportion which according to my experience it is most desirable to use is that of about one gram of alkaloid to 50 cubic centimeters of alcoholic solution. While a greater strength than this does not present any advantage in a tube of 220 millimeters, it is objectionable on account of its obstructing the passage of the light. Quinine combined with Sulphuric Acid.-For the examination of this compound of quinine I prepared a solution which held the same proportion of quinine alkaloid in a given portion of the solution as that contained in the alcoholic solution. The solution was made by taking one gram of dried quinine, dropping it into about 30 cubic centimeters of distilled water, and adding just sufficient sulphuric acid to dissolve it. The quantity was then made up to 50 centimeters with distilled water, and the 220 millimeter tube filled therewith.

At a temperature of 21° C. the average rotation as determined by 100 observations was 11.36°. By the formula

(9)

αχυ

[a]j= X100 we have

Χρ

X100-258-18° at 21° C.

220×1

The temperature of the solution in the tube was then raised. by means of the water jacket, and the average of 100 observations was a=-1073° at 43° C. By the formula

(10)

[a]j=

- 10.73° x 50
220×1

×100=-243.86° at 43° C.

* This solution was employed as being similar to that used by physicians.

The difference in temperature being 22° C. and the difference in rotation 14:32°, we have

1° C. 650° difference in rotation.

That is, for every rise of one degree Centigrade the rotation diminishes 650 or nearly two thirds of a degree in a solution of sulphate of quinine in which there is one gram of alkaloid to 50 cubic centimeters of solution.

Effect of variation in the proportion of water.-A solution of sulphate in water prepared as before and containing one gram of alkaloid to 50 c. c. of solution when examined under a variety of temperatures, gave as the average result

This solution diluted by an addition of 50 c. c. of distilled water by which v was raised from 50 to 100 gave under a similar variety of temperatures the average

Adding 100 c. c. of water to the last solution and thereby raising to 200, gave under the same conditions.

(a.) In the case of the sulphate, as has also been shown by Hesse and others, there is a greatly increased rotation power imparted to the alkaloid by its union with the acid. In the experiments presented the values are: for one gram of alkaloid to 50 cubic centimeters of solution [a]j=-154 30° at 25° C. for the alkaloid: for one gram of alkaloid + sulphuric acid to 50 c. c. of solution in water [a] j=-258·18° at 21° C., which applying the correction of 650° for each degree Centigrade becomes [a]j=-255 48° at 25° C. for the sulphate.

(b.) The aqueous solution of sulphate shows the same changes under the influence of temperature as the alcoholic solution of