In seven of the first seventeen cases the percentage of reducing substance, calculated by the above formulæ, exceeded that given by the copper test, and by a mean amount of .539. In ten of them it fell short and by a mean amount of .938. This method, therefore, can be relied upon to give results which vary from the copper test only by a small amount. Not much more in the way of accuracy can be claimed for the copper test itself. In Nos. 18, 19 and 20 we have again the cases where the high specific gravities vitiate the results of the calculation. CORRECTION FOR SPECIFIC GRAVITY. I next proceeded to investigate a method for correcting the reading of the polariscope for variations caused by changes in the specific gravity of the specimens. First, I determined the percentage of water in glucoses of different specific gravities. Following are the results: These data are scarcely sufficient to establish a rule for correction for variations in specific gravity; but it appears from them that the formula will not vary much from the following. The rule, 53 divisions 53 percentage, seems applicable to samples in which the percentage of IO is 12 to 14 and of which the specific gravity is from 1.409 to 1.414. For each variation of .001 in the specific gravity, the percentage of H2O varies about .3. Thus, if we take the two extreme cases, viz., 6.37 and 15.40 percentage of H.O, we find the corresponding specific gravities to be 1.440 and 1.409, a difference of .031. The difference in the percentage of water is 9.03. The quotient of .0903.031 3 nearly. Let us apply these data to the correction of Nos. 18, 19 and 20 in table IV. I give below these numbers and also their corrections. The above corrections were based on the supposition that 53 divisions of the scale correspond to 53 percentage reducing matter when the specific gravity 1.409 and the percentage water 15. We may therefore construct the following provisional formulæ, for estimating the correction to be applied to the reading of the scale when the specific gravity of the specimen varies much from 1.409. Then a' a3 a (1.409) when the specific gravity is greater than 1.409; and a'a+3a (1.409) when e is less than 1.409. I next propose to undertake some investigations to show the nature and number of the optically active principles present in glucose. THE EFFECT OF HEATING WITH DILUTE ACIDS, AND TREATING WITH ANIMAL CHARCOAL ON THE ROTATORY POWER OF GLUCOSE; WITH NOTES ON THE ESTIMATION OF CANE SUGAR AND GLUCOSE IN MIXTURES. By H. W. WILEY, of Lafayette, Ind. SHAKING dilute solutions of glucose or grape sugar with animal charcoal produces a slimy precipitate. I use the words glucose and grape sugar in their commercial sense. By glucose I mean the thick syrup made from corn starch, and by grape sugar, the solid product made from the same sub stance. By pure glucose I mean the substances present capable of reducing the alkaline copper solution. I will not take time here to discuss the propriety of these names, nor the exact nature of the substances present. I have made some experiments to determine the effect of animal charcoal on the rotatory power of the glucose of commerce. The following are some of the results obtained. In each case 10 grammes of the substance were taken and made up to 100 cc. The observation tube was 200 mm. in length. From these figures it is seen that a glucose may lose nearly 10 per cent. of its rotating power when shaken with animal charcoal. This is a matter of great importance when attempts are made to examine commercial syrups with the polariscope. These syrups are usually highly colored, and require a great deal of bone black and lead acetate to make them fit for polariscopic examination. I have not yet tried the action of lead acetate on the rotatory power of glucose. HEATING WITH DILUTE ACIDS. The following readings as well as those in the preceding part of this paper are divisions on the cane sugar scale. A glucose gave direct reading... I. Heated to 68° with 10 per cent. of its volume of strong sulphuric Loss..... 53°.7 52 .96 .74 Heated for 10 min. at 68° with 10 per cent. of its volume strong 43°.02 The per cent. of reducing substance in the above sample before 62°.50 After........ 65 .58 Increase...... 3.08 Thus a loss of 4.10 on the cane sugar scale corresponded to a |