CHEMICAL SCIENCE. 247 



Still the adhesion continues, and the silicious coating can no longer 

 be removed by washing with water. Hence the soluble silicates are 

 adapted to fix various pigments. In fact this was the first use to 

 which they were made subservient, and they have of late been 

 much employed in Europe for painting. When water-glass mixed 

 with the lighter colors is applied to wood, the alkaline nature of the 

 vehicle betrays itself by a softening and discoloration of the surface, 

 which effects, however, are quite inconsiderable, if the wood is new 

 and clean. Another difficulty is, that the fixed coating, having no 

 elasticity, cannot accommodate itself, like an oily or resinous film, to 

 the expansions and contractions of the wood in wet and dry weather, 

 nor yet to slight inequalities of shrinkage. Still, water-glass paint 

 may do well in places where it is not exposed to alternations of damp- 

 ness and dryness. 



Silicate paint is most suitable for stone, brick, or mortar surfaces, 

 which are unyielding. The best way of applying the silicate of soda 

 as a paint is to put it on in several thin coats, and allow several days 

 to elapse between each application. There are several paints with 

 which it is unfit for mixing, such as white lead and Prussian blue, but 

 zinc white, chalk, yellow ochre, sulphate of baryta, cadmium yellow, 

 Venetian red, green oxide of chrome, umber, lampblack, and ultra- 

 marine will mix with it and make good paint. These colors should 

 be ground up with the water-glass, and before applying them the 

 surface to be painted should receive a primary coat of pure silicate 

 twenty-four hours before the paint is put on. A good silicate of soda 

 should be bright and transparent. A great deal of that which has 

 been sold has been mixed with foreign substances and was unfit for 

 painting purposes. 



Walls plastered with lime-mortar may be rendered very hard, close, 

 and smooth, as well as capable of being washed, by applying a few 

 times a silicate, either alone or mixed with chalk or any coloring ma- 

 terial. 



A mixture of water-glass and peroxide of manganese is recom- 

 mended to be applied to cooking-stoves when they are red-hot, as it 

 is said to make a good blacking, not as liable to burn off as common 

 black lead. 



The binding power of the silicates has been turned to aecount by 

 Kuhlmann in the hardening or " silicatization " of soft porous stone. 

 A tender material, like chalk, may be rendered available for building 

 purposes by repeated saturations with water-glass. And the dura- 

 bility of many buildings already erected is greatly enhanced by sub- 

 jecting the outside surface to a similar treatment. The same process 

 has been found efficacious in preserving some ancient statues freshly 

 exhumed, which would otherwise have fallen to pieces after a short 

 exposure to the air. Fragile palaeontological specimens have also 

 been strengthened and saved by silicatization. 



Ransome says that merely washing stone with water-glass is not 

 sufficient, as the silicate retains its solubility for a long time. He 

 therefore thought fit to secure a patent for fixing the silica by the 

 subsequent application of chlorid of calcium. But, notwithstanding 

 the strong commendations of interested parties, it would appear from 

 recent discussions of the subject in London that this method has not 



