SOLVENTS. J1ost oil paints contain some tur pentine or other volatile solvent. It is generally agreed that turpentine is the hest of these; it is slow to evaipo•ate. and any residue which does not evaporate readily oxidizes into a durable resinous substance, highly elastic, while benzine, which is often used as a substitute, is more rapidly volatile. The turpentine mixture retains its complete fluidity some little time after brush ing out into a film, and so the hrush-marks flow out and disappear, and the whole surface becomes smooth and uniform; hut benzine evaporates im mediately, ;Ind the paint becomes emnparatively stifT and shows brush-marks and all imperfec tions of surface. This is. of course, more marked still in varnishes. Benzine has also a tendency, in some eases, to cause a separation. Kerosene is also used as a substitute for turpentine, but no good paint can he made with kerosene as an ingredient. Artificial turpentines are usually made of high boiling-point benzine or low boiling point kerosene, scented w•itln eucalyptus and other essential oils. They are not to be used.
Finli-PnooF PAtyrs. The best lire-proof paints are made by grinding into each gallon of paint about a pound of boric acid. Some manufacturers use instead a very soft and easily fusible glass which is powdered and used in the same way. The idea is that when exposed to heat the boric acid or the glass will melt and form an air proof glaze over the wood; the boric acid also, being slowly volatile, penetrates the surface with a gas which neither burns nor supports combus tion. None of these paints are at all lire-proof when fresh, as the oil is so combustible as to overcome the restraining influence of the flux; but when the oil has become oxidized, it no longer burns readily, and, of course, the pigment is in almost all cases incombustible, and the protective action of such paint is then very con siderable. The fire-proofing quality of such a paint diminishes with age and exposure, as the boric acid dissolves out and is washed away by the rain.