=Petroleum Spirits.= There are produced from Texas crude oil which has an asphaltum base, and Pennsylvania crude oil which has a paraffin base, high boiling-point petroleum spirits which have come into wide use as paint and varnish thinners. When such materials have the proper evaporating value, high flash-point and freedom from sulphur, they are to be highly recommended as paint thinners. The following shows the analyses of a few of these materials examined in the writer's laboratory: PETROLEUM SPIRITS =======================+=============+============+============== | Texas Base | California | Penna. Base | | Base | -----------------------+-------------+------------+-------------- Color | Water White | White | Water White Specific Gravity | .811 | .79 | .81 Boiling Point | 156 deg. C. | 138 deg. C.| 146 deg. C. Flash-Point | 44 deg. C. | 40.5 deg. C.| 43 deg. C. Residue on Evaporation | .2 | .15 | .12 =======================+=============+============+============== =Benzol.= "Solvent naphtha" or 160-degree benzol is a product obtained from the distillation of coal tar, differing from benzine, a product obtained from the distillation of petroleum. It is a valuable thinner to use in the reduction of paints for the priming of resinous lumber and refractory woods such as cypress and yellow pitch pine. The penetrating and solvent values of benzol are high, and it often furnishes a unison between paint and wood, that is a prime foundation to subsequent coatings, preventing the usual scaling and sap exudations which often appear on a painted surface. Because of the great solvent action of benzol, it should never be used in second and third coatings. The writer has successfully painted inferior grades of cypress with a paint containing benzol in the priming coat. =Benzine.= Benzine is seldom used in paints on account of its rapid evaporation, which is apt to cause pinholing of films and other surface defects. In paints of the dipping type where rapid evaporation is essential, benzine finds its widest application. CHAPTER II A STUDY OF DRIERS AND THEIR EFFECT The proper drying of oils and their behavior with various siccatives in varying quantity is an interesting problem, and obviously of considerable importance from a practical standpoint. Unfortunately there is a decided scarcity of reliable literature dealing with the subject for the guidance of those concerned in the manufacture or application of siccative products. Furthermore, when the problem is investigated, it is not difficult to see why this is so.