On comparison of the arithmetical means of the results obtained in fifty-four trials made during the course of the same day, the striking fact is brought out that the amounts of iodine, liberated by the two acids in the presence of the same base, stand in a constant ratio to one another. The law of actinic force herein indicated may provisionally be expressed by the formula-the chemism of the chlorine radical is to that of the SO, radical (measured by the relative amounts of iodine liberated by each respectively in solutions of the metallic iodides exposed to sunlight), as 1.47: 1. There is reason for inferring from the experiments, that a similar definite ratio exists between the amounts of iodine liberated from different soluble iodides in the presence of the same acid.

Comparison of the Actinic Intensities of the Solar, Electric and Magnesium Light.

In making this comparison, the amounts of iodine liberated at the hour of maximum actinic intensity (1-1.30 P. м.) were taken in the case of the sun. The electric light was that emanating from a lamp of 7000 candle power, falling upon the solutions at a distance of six inches; the magnesium light that derived from the burning of a single ribbon in the ordinary lamp, placed at the same distance. The time of exposure to the electric light was ten minutes to the magnesium light twenty-five minutes: to the sun one-half hour: in the table, all are calculated to one hour.

DIAGRAM II.

COMPARISON OF THE ACTINIC INTENSITIES OF THE SOLAR, ELECTRIC, AND MAGNESIUM LIGHT.

20

222

24

ELECTRIC LIGHT

Calculated to One Hour.

On examining this table, and still more readily, the graphic illustration accompanying it, two phenomena become forcibly manifest:- -1st. The very much greater actinic intensity of the electric as compared with the solar ray, when compared in the manner indicated, and the very much less intensity of the magnesium.7 2nd. Instead of the relative chemism of the chlorine atom, as estimated by its iodine-liberating power under these conditions, being 1.5 in all three cases, it is 2.4 to 3 with the electric, and 10 with the magnesium light. The examination of these differences, as related to the actinic forces of different sources of light and to different acid and basic radicals, is being further investigated.

Finally, the influence of absorbing media upon the invisible rays of the sun and electric light was determined, the comparisontubes being surrounded with a thickness of 3 c.m. of ammoniosulphate of copper, neutral potassium chromate and fuchsine, each solution being brought to the same apparent degree of translucency, for the blue, yellow and red respectively. The exposure to the sun was from 9.30 A.M. to 5.30 P.M.; to the electric light 20 min.; but both are reduced to the interval of 1 hour.

These figures show that the selective action of absorbing media upon the invisible rays of different illuminants varies greatly, and suggests the employment of this method for the mapping out of absorption spectra for the actinic portion: Stevens Institute of Technology, June, 1880.

In order to bring the magnesium curve into the same diagram as the others, the numbers in the magnesium column in the table were all multiplied by ten.

THE ROTATORY POWER OF COMMERCIAL GLUCOSE AND GRAPE SUGAR. A METHOD OF DETERMINING THE AMOUNT OF REDUCING SUBSTANCE PRESENT BY THE POLARISCOPE. By H. W. WILEY, of Lafayette, Ind.

IN "the trade" the name "Grape Sugar" is applied only to the solid product obtained from corn starch. On the other hand, the term "Glucose" is given to the thick syrup made from the same material. I shall use these words in their commercial sense.

INSTRUMENTS EMPLOYED.

I used in the following investigations two polariscopes, made by Franz Schmidt and Hænsch, Berlin.

The readings of these instruments, after correction for displacement, agreed well together.

The one was the instrument ordinarily used, in which the purple ray is employed and the quartz half moons give blue and red tints.

The other was the Laurent "half shadow."

Both of these instruments are graduated to read 100 divisions each equal to 1 per cent. sugar with a solution containing 26.048 grams. pure cane sugar in 100 cc.

In addition to this scale the "half shadow" has another which gives the actual angular rotation. This is especially convenient when the specific rotatory power of a substance is to be determined.

The angular rotation however can be calculated for the former instrument.

For if we take the specific rotatory power of pure cane sugar at 73°.8 we have the following equation:

Each division on the cane sugar scale is therefore equal to 0°.3845 angular measure.

This quantity corresponds to the transition tint. It is different for the differently colored rays.

In the "half shadow" polariscope, an instrument particularly adapted to persons afflicted with any degree of color blindness, the mono-chromatic light, coming from the sodium-Bunsen lamp, passes through a crystal of acid potassium chromate.