~70. Neutral Oil~ (14) seems to be especially adapted for use in horology. Used in a pure state, or mixed in variable quantities with a good animal oil, it can readily be made to fulfill the various conditions required in all parts of watches, chronometers, mantel and tower clocks. It is usually sold as such, but sometimes under the names "liquid paraffine," "glycoline," "albolene," etc., while "solid paraffine," "white cosmoline," "solid alboline," are the names given to the thick butyraceous mass from which neutral oils are made. Sometimes this substance, as well as the liquid paraffine, is medicated or perfumed; but it is hardly necessary to state that when thus treated it is unfit for use in horology. ~71. The Properties of Neutral Oil~ are stated to be:[15] "It is a clear oily liquid, having a specific gravity of not less than 0.840 and boiling not below 360° C. (680° F.). It should be free from colored, fluorescing, and odorous compounds. "When heated for a day by means of a water bath, the paraffine should not become dark colored, and the sulphuric acid should become only slightly brownish. Metallic sodium treated in a similar manner should retain its metallic lustre. Alcohol boiled with paraffine should not have an acid reaction." ~72. The Properties of Solid Paraffine~ (13) are given as follows:[16] "The melting point of commercial paraffine varies much. Obtained from the residuum of petroleum distillation it is usually 43° C. (109.4 F.), or somewhat higher." The acid and metallic sodium tests given for liquid paraffine will apply to the solid paraffine. ~73. The Value of a Lubricant~ _as_ a lubricant is independent of the market price; and it is at a maximum, according to Thurston, when it possesses the following characteristics: 1. Enough "body," or combined capillarity and viscosity (82), to keep the surfaces between which it is interposed from coming in contact at maximum pressures. 2. The greatest fluidity consistent with the preceding requirements, i. e., the least fluid friction allowable. 3. The lowest possible coefficient of friction under the conditions in actual use, i. e., the sum of the two components, solid and fluid friction, should be a minimum. 4. A maximum capacity for receiving, transmitting, storing and carrying away heat. 5. Freedom from tendency to decompose or to change in composition by gumming or otherwise, on exposure to the air (79) while in use. 6. Entire absence of acid or other properties liable to produce injury of materials or metals (77) with which they may be brought in contact. 7. A high temperature of vaporization and a low temperature (83) of solidification. 8. Special adaptation as to speed and pressure of rubbing surfaces under which the unguent is to be used. 9. It must be free from grit and from all foreign matter. The author will add that for use in horology: 10. It must possess a minimum variation of viscosity (84) in varying temperatures.