A Equations. In each equation y is the rotation in degrees, w is the time in half. hours. By placing dy. =0 in each equation, we find the value of x when da y has its highest value. The corresponding value of y is thence calculated by substitution in the equation considered. We thus find data for the comparison of the two acids. These results show that though 2HCl may be the "equivalent" of H SO, in weight for saturation (i.e., in the ordinary sense), it certainly is not the equivalent in the dynamical sense. They also render it highly probably that HCl is equal dynamically to H2SO4. Ostwald, * by a method based on the alteration of the specific volume of solutions, 2HCI has shown that the ratio =1.93, a result which our numbers, H.SO. though not as perfect as we could wish, nevertheless strongly confirm. * "Journ. Prakt. Chem.," N.F. xvi, p. 419. + If the curve equations be examined, it is found that the highest value of y is practically the same in each. By taking the average value = 11°:924, and calculating to specific rotation (assuming that the action involves no change of weight), the number 73.78 is obtained. This falls short of the specific rotation of galactose (83), and seems to point to the dual nature of lactin mentioned in the researches on lactin ; probably at this point the sugar in solution is Fudakowski's lacto-glucose. ("Deut. Chem. Ges. Ber.,” ix, 42-44.) III, “Researches on Lactin." By EDMUND J. MILLS, D.Sc., F.R.S., “ Young” Professor of Technical Chemistry in Anderson's College, Glasgow, and JAMES HOGARTH. Received December 4, 1878. Although lactin, or sugar of milk, has been investigated by numerous chemists, there are many problems connected with it which still await solution. We have accordingly undertaken a series of experiments in connexion with this remarkable compound, in the hope, not only of obtaining special results, but such as may be made available in studies of a more general nature. As our work throughout has been for the most part optical as well as chemical, we have first to state oar methods of obtaining the constant of Jellett's polarimeter, the instrument employed in our investigations. I. Determination of the Polarimeter's Constant.—a. By quinine sulphate. 5.5412 grms. of the sulphate were dissolved in water acidulated with hydric sulphate, and the solution made up to 100 cub. centims. The average of five readings gave a solution of – 250.73, equivalent to a specific rotatory power of - 2320-16. De Gris and Alluard* give - 2550:6, a number which is to our experimental num. ber as 1.10096 to 1. B. By cane sugar. Three sets of experiments on solutions containing respectively 16-3500, 8-1750, and 4:0875 grms. in 100 cub. centims., and embracing five, four, and four readings, gave a general mean reading 21°74, equivalent to a specific rotation 66°48. This is to the generally accepted number (7308) as 1 to 1'11011. 7. By salicin. Two sets of experiments with solutions containing respectively 4.9156 and 2.4578 grms. in 100 cub. centims., and each embracing three readings, gave a general mean reading 4°:92, equal to a specific rotation 50°:046. Bouchardatt gives 55°.832, which is to the number got by Jellett's instrument as 1:11561 to 1. The average of the three numbers, 1.10096, 1.11011, and 1.11561, gives 1:10889 as an experimental factor for converting our Jellett readings into ordinary readings. The relation of the two scales may also be seen by examining the arc divided to read percentages of cane sugar with a solution containing 16-35 grms. in 100 cub. centims. In the Jellett instrument, an arc of 21°.666 is divided into hundredths for this purpose ; and as 16-35 grms. pure cannose read 100 on this scale, the specific rotation *“Compt. rend.,” lix, 201. is 66°256, which is to 730.8 as 1 to 1.11386—a factor which differs from the above experimental one by 0:45 per cent. All the specific rotations given by us are corrected by this factor, and are comparable with those in general use. In all our experiments the specific rotation is calculated by the formula [a]=9V. Where [a]= specific rotation, a = the reading in lp degrees, V the volume of solution containing the weight p, and l = the length of the column in decimeters (in the above experiments, 2). II. Determination of the Permanent Specific Rotation of Lactin.—The lactin was purified by filtration through animal charcoal, and two or three crystallizations, after which it left no sensible residue on ignition in air. Five sets of readings were made : (1.) Average of 5 readings. Specific rotation 52 84 53.23 53:37 53:04 53.07 The general mean of these numbers is 53°12, which, multiplied by the factor 1.11386, gives 59°:17 as the permanent specific rotation of lactin. The number given by Berthelot* is 59°-3. In every experiment, care was taken that the rotatory power of the solution had become constant. Three different samples of lactin were employed. Experiments (1), (2), and (3), were on sample I, (4) on sample II, and (5) on sample III. As the samples were prepared at different times, and by a method varying slightly each time, the very small differences in the results show that the lactin contained little or no impurity. III. Examination of the Law for the Change of Rotation in a freshly prepared Solution of Lactin.-If the rotatory power of an aqueous solution of lactin be examined at short intervals of time, it soon becomes apparent that a change is taking place, the angle through which the plane of polarization is rotated becoming gradually less. The object of the following experiments is to quantify the phenomenon in question. Five grms. of lactin were dissolved as rapidly as possible (time taken, 1 hour 15 minutes) in cold water, and the solution made to 100 cub. centims. The polarimeter tube (2 decims. long) was filled with the liquid, and a first observation taken 15 minutes after complete solution, or 14 hour after first contact. Succeeding readings up “ Ann. Ch. Phys.,” [3], liv, 82 ; lx, 98. |