618 Transactions of the American Institute. 



2. The bichromate of potassa, or red chromate, is the present mate- 

 rial used for all practical purposes, and is prepared from the yellow 

 or neutral chromate of potassa. 



3. The chromic acid, obtained in ruby-red needle crystals from the 

 bichromate. 



4. The chromic oxide, or green oxide of chrome, is a sesquioxide 

 of chrome, is a permanent green pigment, obtained in presence of 

 organic matter ; it is much used in glass making for green, and in 

 printing for the bank note paper of the United States currency. 



5. For bleaching of palm oil, both the bichromate and the chromic 

 acid are employed. 



6. In the preparation of the aniline purple called mauve, by a com- 

 bination of the bichromate and pure aniline. 



7. It has latterly been introduced as a powerful exciting liquid in 

 batteries, possessing many advantages. 



8. In photography the bichromate of gelatine has lately been put 

 to use, from the peculiar property of being soluble in the dark ; but 

 when exposed to the light it becomes insoluble. 



9. In calico printing bichromate of potassa is a powerful auxiliary, 

 for it renders some vegetable colors faster ; also the lead pigments 

 enter on fibrous textures more deeply. 



10. Chromic acid, from its excess of oxygen, forms a powerful 

 bleaching agent. 



11. The various shades of yellow and orange chromates of lead form 

 the most brilliant pigments for painting. 



12. Chromium steel, made from a small admixture of five per 

 cent chromic iron to cast-iron, bears a tensile strain of 140,000 pounds 

 to the square inch. It is extensively used at the St. Louis bridge and 

 Louisville bridge for girders, which have to stand both pressure and 

 expansion. 



13. In medicine the bichromate acts externally as a caustic, and is 

 used for removing warts, also in curing affections of the mucous 

 membrane. 



Yanquelin, in 1797, first obtained the pure chromium metal by 

 exposing green oxide of chromium in a charcoal crucible, kept in a 

 blast furnace for some time ; the pure metal is found at the bottom 

 of the crucible in grains of a gray- white color (between steel and tin), 

 very brittle, not magnetic, but conducting electricity. It is scarcely 

 attacked by cold nitric acid or aqua regia, but readily by hydro-fiuoric 

 acid, evolving hydrogen gas. Its specific gravity is 6.8, and its com- 

 bining weight 52.2. 



