PAINTS, DYES, AND VARNISHES 



adulterated with the cheaper sulphate of barium. And 

 yet, if we may believe the results of the investigations of 

 certain competent but disinterested persons, this prej- 

 udice against the barium pigment is, in part at least, a 

 traditional one, not justified by facts. Such investigators 

 claim to be able to prove by practical demonstration that 

 enamel white is quite as good a pigment as white lead- 

 even better, indeed and that it is destined slowly but 

 surely to replace the more costly and poisonous material. 

 That it has not done so hitherto, they say, is because 

 it is so difficult, even in this age of iconoclasm, to over- 

 throw beliefs that have been accepted as facts for so 

 many centuries. 



Barium sulphate not only resists the action of the 

 atmosphere, but is not affected under ordinary circum- 

 stances either by strong acids or alkalis. It is found in 

 nature as the mineral barytes, or heavy spar, and is 

 sometimes obtained in so pure a state that it may be 

 ground to powder and used as a pigment without further 

 treatment. When treated in this manner, however, it 

 is not so good a pigment as the product of chemical 

 combination, as the particles cannot be reduced to such 

 a fine state of subdivision by the mechanical process of 

 grinding as they are by chemical action. 



When the enamel white is to be made from witherite, 

 as the native barium carbonate is called, this substance is 

 first dissolved in hydrochloric acid, and a solution of 

 barium formed. Sulphuric acid is then added to the 

 solution and in this manner the insoluble barium sul- 

 phate, or enamel white, is formed, and thrown down as 

 an insoluble precipitate. The particles of the barium 



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