[J. F. I.
few weeks' exposure at the window bleached the oil and brought back the blue color. We may consider pigments as transparent substances of high refractive indices. When they are in a mediuln, the quantity of light reflected at the surface of the pigments depends in part upon the relation between the indices of refraction of the medium and pigment. The less this difference, the larger the fraction of light penetrating the pigment and the smaller the part reflected. This accounts for the following : " A chrome yellow, for instance, hecomes deeper in tone and less brilliant when air is replaced by water, and still more deep and lowered in tone when water is replaced by oil." The author ground a number of common pigments used by artists in media of high refractive indices, bromo-naphthalene. 1.65, and methylene-iodide saturated with sulphur. 1.8. White lead ground in the former appeared as a grayish translucent powder, consisting of transparent, doubly refracting crystals. He arranges tim pigments of a given color in order, the first being those that appear transparent in linseed oil and the last that which remains opaque in the medium of highest refractive index. The change of refractive index as linseed oil ages was investigated. In three days the value of the index increased from 1.48 to ~-49. In eight months it rose from 1.492 to 1.5o. " A change in refractive index from 1.48o to 1.5oo causes a perceptible degradation of tone in white lead and makes a pale cadmium yellow appear dull and more orange in tint." The methods of painting in the time of the Van Eycks and later are described and the conclusion is drawn that they made the effect of yellowing neutralize the effect of increase of index of refraction. " T h e painters of that time had thoroughly mastered the possibilities of the oil film, both in the matter of yellowing and of change of refractive index, and there can be no question that under modern conditions of painting in oil, the neglect of these two factors is the explanation of the lowering of tone which so often takes place." G.F.S. F a t Content of Malted Milk.raThe quantitative determination of the fat content of malted milk is a difficult and tedious process, yielding uncertain results. E~WAaD S. Ros~: (Am. J. Phar., I926, 98, 595-596), who has made a study of the various proposed methods, recommends the following procedure. The malted milk (o.5 to I.o gram) is mixed with 5 c.c. of hot water and Io c.c. of concentrated hydrochloric acid; the mixture is heated in a bath of boiling water for five minutes, then is cooled, and extracted by shaking for two minutes with 25 to 3 ° c.c. of a mixture of one volume of washed ether and two volumes of benzin, U. S. P. The extraction is repeated twice with new portions of the solvent. The extracts are combined in a tarred flask; the solvents are removed by evaporation; and the mass of the fat is obtained after drying to constant weight. J.S.H.