Page:The chemistry of paints and painting.djvu/19

 by other chemists. I wish I could have given an authority for every statement not derived from my personal experience, but in an elementary manual treating of many diverse topics such a plan, even if it could have been carried out, would have embarrassed my story with a multitude of perplexing references.

I do not know of any one text-book which covers the same ground as the volume now offered to the public. Several small books on pigments—the most important of all the materials employed by the artist — have indeed been lately published, but the chemical information they afford is generally meagre, and sometimes far from exact. One recent little brochure, which lies before me, has, I confess, caused me some amusement not wholly unshaded with regret. The writer does not pose as a humourist, yet he tells us, when we test for lead in cadmium red, first to mix the sample with white lead before applying the usual test for that metal. Chinese vermilion, he informs us, is sulphide of arsenic, though it is really sulphide of mercury. The presence of sulphides of baryta and lime is stated in one place to lend a softness to the chromates of lead ; as these sulphides instantly blacken these brilliant chromates, perhaps they may be said to soften them. Cœruleum, a stannate of cobalt, is directed to be made of carbonate of soda, powdered flint, and oxide of copper, its two essential constituents, the oxides of tin and cobalt, not being named. These and many other equally preposterous statements and directions may afford merriment to the chemist, but