CHAPTER XL 



POTASSIUM BICHROMATE (BICHROME)- CHROME ALUM— POTASSIUM 

 PERMANGANATE— MANGANESE SULPHATE— NICKEL SULPHATE- 

 COBALT SULPHATE. 



73. Potassium Bichromate, K.^Cr^O- ; 74. Chrome Alum, 



K.,SO^Cr.,(SO^).j24HoO. — Preparation. — Bichromate of potash is ob- 

 tained commercially by calcining chrome ore on the sole of a rever- 

 beratory fm-nace with half its weight of nitrate of potash. The mass 

 is then lixiviated with water and acetic acid added to saturation. 

 Whilst precipitating silica and alumina this acid converts the neutral 

 chromate into bichromate. After filtration the liquor yields, when 

 concentrated, orange crystals of bichromate of potash. Chrome alum 

 is obtained by treating a solution of 150 lb. of " bichrome " with 250 

 lb. of sulphuric acid and 60 lb. of alcohol. 



Properties. — Crystals of " bichrome " are permanent in the air.. 

 They dissolve in ten times their weight of water at 29" C. Chromates 

 are very poisonous ; in small doses they produce by a specific slow 

 poisoning caries of the bones of the nose. 



Action of Chrome Salts on Plants. — Chrome salts, chiefly 

 chromates, are poisonous to plants. H. Coupin in 1898 determined 

 the toxicity of the different chrome salts by adding them to a nutritive 

 solution ; he found that the following quantities disturbed the growth 

 of cereals : — 



TABLE XXIV. — Shoxving the Toxiz Dose of Different Chrome Salts in a 

 Ntitritive Solution (Coupin). 



Chrome alum 

 Chromium sulpliate . 

 Chromic acid 

 Potassium chromate . 

 Bichromate oi potasli 

 So'iium cliromate 

 Bichromate of toda . ■ . 

 Ammonium chromate 

 Bichromate of ammonium 



Action of Chromium Salts on Parasitic Fungi. — It follows from 

 Hitchcock and Carleton's experiments that w^hilst a 1 per cent solution 

 of chrome alum has no action on the uredospores of the Piiccinia 

 coronata, Corda, a 1 per cent solution of bichromate of potash lowers 

 considerably the germinating capacity of these spores after twenty- 

 four hours' immersion and destroys them by more prolonged contact. 

 A 01 per cent solution his no action on the uredospores, but if the 

 (189) 



