Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/418

410 use of linseed oil is a good preservative, and so is a covering of copal varnish, but these can be applied to small articles only. Another application is sulphur which has been immersed in nitric acid and distilled to dryness, which, being exposed to the air, dissolves into an oil, the parts to be secured from the worm are to be anointed with this oil, which does not give an unpleasant odor to the wood. Lime is an excellent prevention against the worm, and sap-wood should always be impregnated with it when used in a dry situation. As worms do not attack bitter woods, soaking wood in an infusion of quassia has been tried, and is said to have the desired effect.

Zinc, To prepare for painting. In 64 parts of water, dissolve 1 part of chloride of copper, 1 of nitrate of copper, and 1 of sal ammoniac, and add 1 part of commercial hydrochloric acid, brush the zinc over with this mixture, which gives it a deep black, leave it to dry for twenty-four hours, when any oil color will firmly adhere to it, and withstand both heat and damp.

A Useful Cement. Alum and plaster of Paris, mixed with water and used in the liquid state, form a hard composition and a useful cement.

Barytes in Chrome Yellow. The detection of baiytes in chrome yellow is a very simple matter, and as it is a very commonly employed adulterant, the following may be found useful: Put a small portion of the yellow into a test tube, add a sufficient quantity of concentrate muriatic acid, and boil. The yellow is almost immediately resolved into a white semi-crystalline chloride of lead and a green solution of chloride of chromium. A large amount of water is added to the test, which is again boiled. If there is no barytes present, a clear solution will be formed, as chloride of lead is soluble in boiling water. The barytes, if present, will be left behind as a heavy, fine white deposit, which may be washed by repeatedly boiling with water.

Bathrooms. These should be warm in coloring, to assist