2 14 16 18 20 DIAGRAM II. COMPARISON OF THE ACTINIC INTENSITIES OF THE SOLAR, ELECTRIC, AND MAGNESIUM LIGHT. 122 ELECTRIC LIGHT MILLIGRAMMES OF IODINE LIBERATED. 2KI+2HCL MAGNESIUM 10 Calculated to One Hour. 24 [Magnesium light multiplied by 10.] 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. 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. The ray thus produced is less rotatable than the "transition tint." When the instrument gives 100 divisions on the sugar scale, it shows an angular rotation of only 34° 42′ = 34°.7. One division therefore of the sugar scale is equal to 0°.347 angular measure. To determine the specific rotatory power of cane sugar for the sodium-acid potassium chromate we use the following ray, equation. Sp. rot. pr. = 34°.7 X 100 = 66°.6 To determine the specific rotatory power for any other substance which has been determined for the transition tint, we multiply by the factor .9024. Thus, if we take the specific rotatory power of dextrin for the transition tint at 139°, for the "half shadow tint it will be 139° X .9024 = 125°.4. These data rest upon the accepted formula; 66 66 € = amount of substance in one gramme of the solution. specific gravity of solution. 66 入 length of observation tube. 66 wweight of substance in grammes. MATERIAL. The glucoses studied in the following examinations were made by the Peoria Grape Sugar Company. I am under obligations to Mr. Wm. Allen, the superintendent, for many favors in connection with my work. The grape sugars were made in Buffalo. ROTATORY POWER. The average value of 0 for the "half shadow" ray is nearly 85°. For the purple ray it is nearly 94°. It however varies extremely in different samples. The following table will show the range of these variations:Showing Variations of 0 in different Specimens of Glucose and Grape Sugar, together with the Specific Gravities of the same. From a study of this table it is seen that within small limits 0 is independent of the specific gravity of the solution. Nos. 14 and 15 were grape sugar and the specific gravity is much higher here than in the glucoses, while the value of is much less. Where the increase in density however is considerable, as in 3 and 17, there is also a marked increase in the value of 0, although this increase is not proportional to the increment of specific gravity. In masses of homogeneous nature and structure we should expect a priori that 0 would always be proportional to the density of the body, i. e., to the amount of optically active matter in a unit number of grammes. It is thus seen without further argument that commercial glucoses are not optically homogeneous, even when made in the same factory and by processes which do not sensibly vary. A further study of these optical reactions convinced me that the rotatory power of commercial glucose increased, as the percentage of reducing substance diminished. The following table shows the value of 0 and the corresponding percentage of reducing matter as obtained by Fehling's solution. |