CHROMATES. Ill 



warm and deep vessel of silver, iron, porcelain, or stoneware, 

 with a smooth inner surface. After cooling, the lower part 

 of the fused mass, containing iron, may be cut off hj a sharp 

 tool. If the heat be carried to full redness, the resulting salt 

 will hafe a gray color, from the separation of carbon 

 through it. 



To prepare cyanide for galvanic gilding or silvering, both 

 the prussiate and carbonate of potash should be free from 

 sulphate, as the consequent formation of sulphuret injures the 

 color of both gilding and silvering. — Eisner. 



4. Chromates. — Chrome yellow and other beautiful pigments 

 and dyes are obtained from the mineral chromic iron, which 

 is, in its purest form, FeO,Cr303, which should contain 68 

 per cent, of oxide of chrome. Mr. T. Garrett analyzed a 

 specimen of the ore from Tyson's mine, Lancaster county, 

 Pennsylvania, containing 63 per cent., which approached nearer 

 to the formula than any published analysis. The ore at this 

 and one or two other places forms solid veins or masses, but 

 a great deal is obtained in the form of sand, by washing 

 the sandy beds of the small streams flowing from a range of 

 serpentine-rock. 



B. Silliman, Jr., first observed that the green coating on 

 the ore of Tyson's mine was a hydrocarbonate of nickel. T. 

 Garrett found the same metal in some of the ore where the 

 green coating had been carefully removed, and he has since 

 proved that it contains a trace of tin. Garrett's analyses 

 were performed in my laboratory, where he is still investigat- 

 ing some of the minerals of the chrome localities. — J. 0. B. 



Jacquelain's process (Dingler's Pol. Journ. cvi. 405) for the 

 manufacture of potassa-chromate from the natural chromo- 

 ferrite is as follows. The finely-powdered ore is to be inti- 

 mately incorporated with chalk, and this mixture exposed in 

 strata of 1| inches, for 10 hours, to the heat of a reverbe- 

 ratory furnace. Neutral chromate of lime is tlius formed, and 

 the next step is to convert it into bisaltf. This is to be done 

 by grinding it, and, while suspended in water, adding a slight 

 excess of sulphuric acid. To separate any protosulphate of 



