The Romance of Modern Chemistry

FATS AND OILS occupies about three days, but the process may be con- siderably accelerated by a certain device, as was shown long ago by a Dutch artist. He found that if the ordinary or raw linseed oil were previously heated to a high temperature with lead oxide, the time required for drying was shortened to six or eight hours—an observation which has turned out to be a very valuable contribution from art to practical science. At the present day linseed oil which is to be used in the manufacture of paints is subjected to a preliminary treatment of the kind suggested by the Dutchman, the only differences being that the temperature now employed is not so high (only about 300° Fahrenheit), and other driers besides lead oxide may be used. The product is known as boiled oil, although, strictly speaking, it has never been boiled at all, but only heated; fatty oils would, as a matter of fact, decompose if we attempted to boil them. The name “ boiled ” oil is one of those little inaccuracies of terminology which one comes across occasionally in the technical world—a “terminological inexactitude,11 the politicians would call it. The case is parallel to black lead,” which, as the reader will have learned from chapter v., contains no lead at all. As already indicated, boiled oil is extensively used in the preparation of paints and varnishes. The colour- ing material, white lead, lampblack, ultramarine, or red lead, as the case may be, is first ground with a small quantity of linseed oil and then mixed with more oil, generally of the boiled variety, and with oil of turpentine. When a layer of the paint is spread on a surface of metal or wood it dries quickly, and a pro- tective skin is left. The drying of wet paint, the reader will now perceive, is quite different from what takes 241 □