One grave objection to this instrument is found in the absence of the proper scientific spirit controlling its manufacture and sale, as evidenced by the attempt to preserve the secret of the composition of the typical oil and the negligence in testing the scale of the instruments which will be pointed out further along. According to Jean[252] the common oils, when purified, give the following readings at 22°: Peanut oil +3.5 to +6.5 Colza ” +17.5 ” +21.0 Cotton ” +18.0 ” +18.0 Linseed ” +47.0 ” +54.5 Lard ” +5.5 ” +5.5 Olive ” +1.5 ” 0.0 Sesamé ” +17.5 ” +19.0 Oleomargarin -15.0 ” -15.0 Butter fat -30.0 ” -30.0 Mutton oil 0.0 ” 0.0 Fish ” +38.0 ” +38.0 In this instrument, therefore, vegetable and fish oils, as a rule, show a right hand, and animal fats a left hand deviation. The oleorefractometer has been extensively used in this laboratory and the data obtained thereby have been found useful. We have not found, however, the values fixed by Jean to be constant. The numbers for lard have varied from -3.0 to -10.0, and other fats have shown almost as wide a variation from the values assigned by him. Jean states that the number for lard, determined by the oleorefractometer, is -12, and he gives a definite number for each of the common oils and fats. On trying the pure lards of known origin in this instrument, I have never yet found one that showed a deviation of -12 divisions of the scale; but I have no doubt that there are many such lards in existence. The pure normal lards derived from the fat of a single animal would naturally show greater variations in their chemical and physical properties, than a typical lard derived from the mixed fats of a great many animals. In leaf lard, rendered in the laboratory, the reading of the oleorefractometer was found to be -10°, while with the intestinal lard it was -9°. On the other hand, a lard rendered from the fat from the back of the animal showed a reading of only -3°, and a typical cottonseed oil a reading of +12°. According to the statement of Jean, a lard which gives even as low a refractive number as -9, by his instrument, would be adjudged at least one-quarter cottonseed oil. After a thorough trial of the instrument of Jean, I am convinced that it is of great diagnostic value, but if used in the arbitrary manner indicated by the author it would lead to endless error and confusion. In other words, this instrument is of greater value in analyses than Abbe’s ordinary refractometer, because it gives a wider expansion in the limits of the field of vision, and therefore can be more accurately read, but it is far from affording a certain means of discovering traces of adulteration with other fats.