=300. Variations in the Instruments.=—In the use of the oleorefractometer, attention should be called to the fact that, through some negligence in manufacture, the instruments do not give, in all instances, the same reading with the same substance. Allen obtained the following data with a sample of lard examined in three instruments, _viz._, 4°.5, 6°, and 11°. Such wide differences in the scales of the instruments cannot fail to disparage the value of comparative determinations. The variations in samples of known origin, when read on the same instrument, however, will show the range of error to which the determinations made with the oleorefractometer are subject. Pearmain has tabulated a large number of observations of this kind, covering 240 samples of oils.[253] Following are the data relating to the most important oils. AT 22°. Highest Lowest Mean reading. reading. reading. Name of oil. Degrees. Degrees. Degrees. Almond 10.5 8.0 9.5 Peanut 7.0 5.0 6.0 Castor 42.0 39.0 40.0 Codliver 46.0 40.0 44.0 Cottonseed (crude) 17.0 16.0 16.5 ” (refined) 23.0 17.0 21.5 Lard oil -1.0 0.0 0.0 Linseed (crude) 52.0 48.0 50.0 ” (refined) 54.0 50.0 52.5 Olive 3.5 1.0 2.0 Rape 20.0 16.0 17.5 Sesamé 17.0 13.0 15.5 Sunflower 35.0 35.0 35.0 Tallow oil -5.0 -1.0 -3.0 Oleic acid -33.0 -29.0 -32.0 AT 45°. Butter -34.0 -25.0 -30.0 Oleomargarin -18.0 -13.0 -15.0 Lard -14.0 -8.0 -10.5 Tallow -18.0 -15.0 -16.0 Paraffin 58.5 54.0 56.0 [Illustration: FIG. 94.—BUTYROREFRACTOMETER.]