SCIENCE IN THE INDUSTRIAL WORLD 



sulphate thus formed are so tenuous that they will pass 

 through the finest filter a state of subdivision that can- 

 not be approached by any known process of grinding. 

 As the finer particles make the better pigment, it is 

 obvious that the enamel whites prepared artificially are 

 better than those prepared from the natural product. 



Another pigment that in many respects compares 

 favorably with white lead, and which is only slightly less 

 permanent than enamel white, is zinc oxide, known com- 

 mercially as "zinc white." In point of cost it has a 

 disadvantage, costing somewhat more than white lead. 

 On the other hand, ten parts of zinc-white paint are said 

 to have as great covering power as thirteen parts of 

 white lead, so that the initial cost is practically offset 

 by the results. 



The zinc white of commerce comes on the market as 

 a product from the zinc smelting-works, as it is formed 

 when zinc vapor is burned in the air. It has the advan- 

 tage over the lead pigments of mixing with pigments 

 that contain sulphur without alteration. And since it 

 is much lighter than the lead compounds, it is better 

 adapted to mixing with the lighter vegetable pigments, 

 such as the lakes. 



The white pigments just described may be taken as the 

 most important ones for commercial purposes. There 

 are a few others, such as those made from antimony 

 compounds, and from bismuth, tin, manganese, and 

 magnesia, which are of practical value for certain 

 special purposes, but even in the aggregate these 

 are relatively unimportant as compared with the lead 

 and zinc compounds. 



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