M. TECHNOLOGY. 537 



blue powder, which lost much in intensity of color by extreme 

 pulverization. Uncombinecl grains of sand disseminated 

 through it could be recognized with a lens, and before the 



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blow-pipe it afforded a brownish frit. Even concentrated 

 acids had very little or no effect upon it. Analysis showed 

 it to consist of silicates of copper, lime, soda, iron, and alu- 

 mina, without even a trace of cobalt. It was found possible to 

 imitate it by heating, under certain precautions, an intimate 

 mixture of white sand, black oxide of copper, chalk, and dry 

 carbonate of soda. 5 (7, xxv., August 27, 1874, 200. 



WEIGHTING SILK WITH SULPHATE OF BARYTA. 



Chevalier treats the raw silk ten minutes in a boiling 

 solution of Glauber's salt, of 26 Baume, then immerses ten 

 minutes in a boiling solution of chloride of barium, of 34 



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Baume, and finally washes. The operations are repeated 

 several times, according to the strength of the charge de- 

 sired. The baths should be alkaline, but their temperature 

 and degree of concentration may be greatly varied, as the 

 circumstances require ; the former may even be as low as 50. 

 All the usual operations can be carried out afterward. 6 (7, 

 ApfU-16, 1874, 159. 



ARTIFICIAL COLORATION OF METALS. 



A method for giving various tints to metals has lately 

 been devised, and consists in coating their surfaces with a 

 thin film of sulphide. It is said that in a few minutes ar- 

 ticles of brass may be coated of any color varying from gold 

 to copper-red, then to carmine, dark red, and through the 

 several shades of blue, according to the thickness of the 

 coating employed. The colors are said to possess good lus- 

 tre, and, if the articles to be coated have previously been 

 well cleaned, the coating will adhere with sufficient firmness 

 to admit of polishing. The coloring solution is prepared as 

 follows: Dissolve 1^ oz. of hyposulphite of soda in 1 pound 

 of water, and add - oz. of acetate of lead dissolved in -J 

 pound of water. If this clear solution is heated to say 200 

 Fahr., it decomposes slowly and precipitates sulphide of 

 lead. If a metallic surface is present, a portion of the sul- 

 phide is deposited thereon, and according to the thickness 

 of this deposition will its color varv, as above described. 



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