15°.5 40° _d_ ------ = 0.91181; _d_ ----- = 0.89679; 4° 4° 100° and _d_ ---- = 0.85997, 4° indicating the relative weights of the sample under examination at 15°.5, 40°, and 100°, respectively, to water at 4°. =289. Densities of Common Fats and Oils.=—It is convenient to have at hand some of the data representing the densities of common fats and oils, and the following numbers are from results of determinations made in this laboratory:[238] 15°.5 40° 100° Temperature. _d_ = -----. _d_ = ---. _d_ = ----. 4° 4° 4° Leaf lard 0.91181 0.89679 0.85997 Lard stearin 0.90965 0.89443 0.85750 Oleostearin 0.90714 0.89223 0.85572 Crude cottonseed oil 0.92016 0.90486 0.86739 Summer ” ” 0.92055 0.90496 0.86681 Winter ” ” 0.92179 0.90612 0.86774 Refined ” ” 0.92150 0.90573 0.86714 Compound lard ” 0.91515 0.90000 0.86289 Olive oil 0.91505 0.89965 0.86168 =290. Melting Point.=—The temperature at which fats become sensibly liquid is a physical characteristic of some importance. Unfortunately, the line of demarcation between the solid and liquid states of this class of bodies is not very clear. Few of them pass _per saltum_ from one state to the other. In most cases there is a gradual transition, which, between its initial and final points, may show a difference of several degrees in temperature. It has been noted, further, that fats recently melted behave differently from those which have been solid for several hours. For this reason it is advisable, in preparing glycerids for the determination of their melting point, to fuse them the day before the examination is to be made. The temperature at which a glycerid passes from a liquid to a solid state is usually higher than that at which it resumes its solid form. If, however, the change of temperature could be made with extreme slowness, exposing the sample for many hours at near its critical temperature, these differences would be much less marked.