JOURNAL OF THE CHEMICAL SOCIETY, TRANSACTIONS. I.-Influen of Temperature on the Refractive Power and on the Refraction Equivalents of Acetylacetone and of Ortho- and Para-toluidine. By W. H. PERKIN, Ph.D., F.R.S. IN 1892, I communicated to the Society a description of an apparatus for determining the refractive power of compounds at different temperatures, together with some results obtained by its use (Trans., 1892, 61, 287). In two later communications, an account was given of the magnetic rotation of substances supposed to contain acetyl, or to be of ketonic origin (Trans., 1892, 61, 800, and 1894, 65, 815); in these it was shown, from their magnetic rotations, that some di and tri-ketonic compounds are tautomeric, and that when heated they change in varying degrees from their hydroxylic, or unsaturated form, to their saturated, or ketonic form, the rotations becoming lower in consequence. The refractive power of several of these compounds was also taken at different temperatures, showing changes in reference to this property, of the same order as in the case of the rotations; this was expected because it has been shown (Gladstone and Perkin, Trans., 1889, 55, 750) that there is an analogy in most cases between the variations in the rotation and refraction of the same compounds. Among the substances examined, acetylacetone, methylacetylacetone, allylacetylacetone, and diacetylacetone were shown to undergo internal change, in the most striking manner, by change of temperature. Since the account of these experiments was published, Brühl, in his VOL. LXIX. В interesting paper entitled a " Study of Tautomerism," gives the results he obtained on the refractive power of acetylacetone at temperatures wide apart; the numbers, however, do not agree with mine, and the same is the case with some of his more recent measurements of the refractive power of para- and ortho-toluidines (Zeit. phys. Chem., 1895, 16, 216). Knowing the great care Professor Brühl takes in making his determinations, I have been induced to repeat my measurements of acetylacetone and the two toluidines, to see if any error could be discovered in the previous work, or any other explanation found of these discrepancies, for it is of great importance from a theoretical point of view to find out whether the analogy between the refraction and magnetic rotation of the di- and triketonic and other compounds, which my results are supposed to indicate, exists or not. In all my determinations, I have used the apparatus described in this Journal a few years ago (Trans., 1892, 61, 288), which is simply a hollow prism containing the substance under examination, heated in an air bath. In making the observations, readings were invariably taken from both sides of the prism, and the sum of the result divided by two, so that if any slight shifting of the zero took place during the raising of the temperature (which, however, does not appear to occur) it would not influence the result. I understand from Professor Brühl that in his determinations of the refractive power of acetylacetone, and I presume also in that of the toluidines and other substances, where temperatures above that of the atmosphere are employed, he used the total refractometer which he has described (Ber., 1891, 24, 286). The following results were obtained with acetylacetone. The specimen employed was that given to me by Professor Claisen, and referred to in the Transactions (1892, 61, 844) as Specimen II. The first set of results marked " A," given below, were made some time since, the product being previously distilled under the ordinary pressure. The other three, marked "B," were obtained quite recently; for these the acetylacetone was redistilled under reduced pressure the day before it was examined, and, as the specimens were not quite identical, the results have been kept separate. For the purposes of this paper it will only be necessary to give the numbers for the three hydrogen lines. A. Ha 99-20 The following are the results obtained at higher temperatures. 1.40210. 99-0° B. HB 99.2 1.41604. 1-40240. 99.0° 1.41656. 99.0° 1-42605. The results already published, obtained by the examination of the acetylacetone, given to me by Professor Dunstan (Trans., 1892, 61, 840, 847), called "Specimen I," although represented by slightly lower numbers than those given above, exhibited very similar differences for variations of temperature. For 88.3° they are 1·103, |