456 M. Wohler on the preparation of Metallic Chromium. 



that the zinc begins to boil, the heat is lessened and the mixture 

 kept for some time in a state of fusion. The crucible is then 

 removed and allowed to cool. 



On breaking the crucible a fine regulus is obtained, covered 

 by a green slag. By successively treating this with dilute nitric 

 acid, the chromium is obtained as a crystalline powder, which, to 

 remove all traces of lead, is at last treated with strong nitric 

 acid. In one experiment, 30 grms. of scsquichloride yielded 

 7 grms. of chromium. Calculation requires ten parts. 



Chromium so prepared is a light-grey, crystalline, glistening 

 powder : magnified fifty times, it is seen to present tree-shaped 

 crystalline aggregates with occasional acute rhombohedra of 

 great lustre, and almost tin-white colour. Its specific gravity is 

 6"81 ; and it has no action on the magnetic needle. Heated in 

 the air, it assumes a superficial yellow and blue coating like steel : 

 a layer of green oxide is only formed after the lapse of some time. 

 It burns with sparks when thrown in an oxygen-alcohol flame, 

 but less brilliantly than iron. It is dissolved by dilute hydro- 

 chloric acid, with disengagement of hydrogen and formation of 

 blue protochloride. 



The chromium was found on analysis to be perfectly free from 

 zinc. 



Scsquichloride of chromium is readily reduced by magnesium, 

 but this metal has no advantage over zinc. The employment 

 of cadmium is not advantageous. 



Wobler further gives the following method for the ready pre- 

 paration of scsquichloride of chromium. 



A mixture of lampblack and sesquioxide of chromium is made 

 into a stift' paste with starch, and formed into pellets which are 

 ignited in a covered crucible. They are then transferred to a 

 crucible with an aperture in the bottom, in which a piece of nar- 

 row porcelain tube 5 or 6 inches long is fitted. One end of the 

 tube projects just above the bottom, and is covered with a very 

 small crucible to prevent the pellets falling through. To the 

 large crucible a second is luted, which is likewise provided with 

 an aperture to carry oft' the gases. The apparatus is then so placed 

 on the grate of an ordinary wind-furnace that the porcelain tube 

 projects below the grate ; it is here connected with a chlorine- 

 generator. When the apparatus is full of dry chlorine, the lower 

 crucible is heated to strong redness, and the heat so regulated 

 that the scsquichloride volatilizes, and condenses in the upper 

 part of the apparatus. 



As the scsquichloride is converted into oxide by being heated 

 in the air, it is important to continue the passage of gas after 

 the oi)eration is ended, until the crucible is quite cool. The 

 scsquichloride of chromium takes up chloride of aluminium from 



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