Manufacturer and builder 10 / 1869
Chrome alum is a residue left during the manufacture of violet and green aniline and of valerianic acid. No market exists for this substance in its raw state, as it can not be used as a mordant, the calcination it has undergone having rendered it insiluble in water. Mr. Jean, in a recent communication to the Academy of Sciences of Paris, proposes the following mode of treating this substance: Pulverize the chrom iron; mix it with charcoal; heat it to a red heat in a refractory crucible. When sulphurous acid gas is no longer disengaged, the first part of the operation is completed. The residue left after calcination is formed of a mixture of sulphate of potash and of sesqui-oxide of chromium. By boiling it in water, the sulphate of potash dissolves, leaving the insoluble chrome salt behind. The green color of the sesqui-oxide of chromium obtained in this manner is too dirty to allow it to be used as a paint or pigment, but on account of its great purity it is an excellent material for the manufacture of bichromate of potash. Its employment for this purpose will tend to diminish the cost of producing the aniline colors, to which it owes its origin.