800 CHROME STONE 



kept at a bright red boat for from 18 to 20 hours in a reverberatory furnace, the mix- 

 ture being turned over frequently, so that all parts may be exposed equally to heat 

 and air ; the temperature is not to rise high enough to cause even incipient fusion, and 

 the charge should be kept in a porous state ; when, on being examined, the charge is 

 found to contain the proper quantity of alkaline chromate, it is withdrawn from the 

 furnace and lixiviated with water. 



In treating chromium (chromate of iron), the ore is pulverised and mixed -with 

 common salt, muriate of potash, or hydrate of lime, and exposed in a roverberatory 

 furnace to a red or even a white heat, the mixture being stirred every ten or fifteen 

 minutes, and steam at a very elevated temperature introduced during the operation, 

 until the desired effect is obtained, which may be ascertained by withdrawing a 

 portion from the furnace and testing it, as customary. The products of this operation 

 are finally treated in the manner usual for the chromic and bichromic salts. 



The mixture of chromium and common salt produces chromate of soda, the greater 

 portion, or perhaps all of the iroa contained in the chromium being absorbed by the 

 hydrochloric acid evolved from the salt, and carried off in the form of sesquichloride 

 of iron. From the first mixture is manufactured pure bichromate of soda, which, by 

 the addition of hydrochloric acid, may be converted into chlorochromate ; and from the 

 last, or lime mixture, is produced a chromate of that earth, from which, by the 

 addition of soda or potash, there may be obtained a compound salt, which, with those 

 previously mentioned, may be advantageously employed. 



M. Jacquelin first prepares chromate of lime by calcining at a bright red heat in 

 a reverberatory furnace, for 9 or 10 hours, an intimate mixture of chalk and chrome 

 ore. The friable and porous mass is then crushed, suspended in water, and sulphuric 

 acid added until the liquid slightly reddens blue litmus-paper ; the chromate of lime 

 is hereby converted into bichromate ; chalk is now added, until the whole of the 

 sesquioxide of iron is precipitated, and the clear liquid, which now contains only 

 bichromate of lime and a little sulphate, may be used for the preparation of the in- 

 soluble chromates of lead, zinc, baryta, &c., by mixing it with the acetates or chlorides 

 of these metals. To prepare bichromate of potash, the bichromate of lime is mixed 

 with solution of carbonate of potash, which gives rise to insoluble carbonate of lime, 

 which is easily washed, and a solution of bichromate of potash which is concentrated 

 and set aside to crystallise. 



Mr. Booth (patent sealed Nov. 9th, 1852) mixes powdered chrome ore with one- 

 fifth of its weight of powdered charcoal, and heats it on the hearth of a reverberatory 

 furnace, protecting it carefully from the air. The ore is by this means decomposed, 

 and the iron reduced to the metallic state, and is dissolved out by dilute sulphuric 

 acid ; the residue is washed and dried, and afterwards mixed with carbonate of potash 

 and salpetre, and heated in the same manner that the chrome ore itself is heated in 

 the process iisually employed. The solution of sulphate of iron is evaporated to 

 crystallisation so as to produce copperas in a state adapted for commerce. 



Analysis of Chrome Iron Ore. Various methods have been proposed. The following, 

 suggested by Mr. T. S. Hunt, gives accurate results : The ore, finely levigated in an 

 agate mortar, is mixed with 10 or 12 times its weight of fused bisulphate of potash, 

 and preserved at a gentle heat for about half an hour. The fused mass is extracted 

 with hot water, and boiled for a few minutes with excess of carbonate of soda ; the 

 precipitate is dried and fused with five times its weight of a mixture of equal parts 

 of nitre and carbonate of soda, in a platinum or silver crucible. The mixture is 

 kept in fusion for 10 or 15 minutes, and when cold is extracted with water. The 

 alkaline chromate thus obtained may be precipitated by a salt of lead, or it may be 

 supersaturated by hydrochloric acid, and boiled with alcohol, by which it is converted 

 into chloride of chromium, from which the oxide is to be precipitated by adding 

 ammonia in excess and boiling for a few minutes. Chrome iron ore is so difficult 

 of decomposition, that the method of fusing it at once with nitre and an alkaline 

 carbonate frequently fails in oxidising the whole of the chromium into chromic acid. 

 Mr. Calvert mixes the well-pulverised ore with three or four times its weight of a 

 mixture made by slaking quicklime with caustic soda, and then dries and calcines 

 the mass. He then adds one-fourth part of nitrate of soda, and calcines for two hours 

 more, by which time he finds the whole of the chromium is converted into chromic 

 acid. Another process, which Mr. Calvert finds to produce good results, consists in 

 calcining the pulverised chrome ore with nitrate of baryta, adding a little caustic 

 potash from time to time towards the end of the process. H.M.K 



CHROME RED and CHROME YEXiXiOW. See CHHOMATES OF LEAD. 

 CHROME STONE. The name given to Chrome Ochre when it is so intimately 

 mixed with the rock in which it is contained as only to be separated from it by chemical 

 means. Such mixtures are met with at Creuzot in France, Waldenberg in Silesia, 

 Mortenberg in Sweden, and elsewhere. See Bristow's ' Glossary of Mineralogy.-' 



