VI. METALS.— SuB-sALTs. 251 



of protoxide of iron. By evaporating the solution nearly to dry- 

 ness, the acid and oxide are decomposed, water is formed, and a 

 solid combination of iodine and iron remains, containing 12G parts, 

 or one atom, of the former, and 28 parts, or one atom, of the 

 latter. The ioduret of iron is deliquescent ; when pure it is of an 

 iron-grey colour, brittle and crystalline in texture like antimony ; 

 when dry, it is inodorous, and when moistened, it exhales the 

 odour of iodine. Dr. Thomson, who was the first to use this 

 preparation medicinally, administers it in those cases in which the 

 capillary system requires to be stimulated, and the tone of the 

 habit to be brought up to the healthy standard. The dose is 

 2, 3, or 4 grains in distilled water, three or four times daily. It 

 is stimulant, tonic, and aperient ; it has been found serviceable in 

 amenorrhcca and leucorrhoea ; from its supposed influence in 

 improving the hematosis, it has been given in phthisis. 



Feriii suBCAiiBONAS, P. L. 1815. Precipitate a solution of 

 8oz. of green vitriol in water, by a solution of 6oz. of subcarb. 

 of soda. 



COBALT. 



Cobalt blue. Wash lib. zafFre to separate as much of the 

 sand as possible ; pour on it 8oz. nitric acid, diluted with an equal 

 weight of water ; digest for some hours, pour oft* the solution, 

 and add fresh acid to the zaffi'e as long as it seems to extract any 

 colour from it ; mix the coloured solutions, evaporate nearly to 

 dryness, dissolve in warm water, filter the liquor, add to the fil- 

 tered nitric solution of the zafFre a solution of phosphate of soda 

 as long as any sediment falls. Wash this violet subphosphate of 

 cobalt, and mix it while still wet with 8 times as much alumine 

 fresh precipitated (from alum-water by a more than sufficient 

 quantity of liquid ammonia), well washed and still wet. Stir till 

 the colour is quite uniform, then dry, and lastly, heat it cherry-red 

 in a crucible. 



2. Dissolve regulus of cobalt, or bright white Cornish cobalt 

 ore previously roasted, in nitric acid, and proceed as already pre- 

 scribed. 



3. riiLijiiuuc tiie nitrate of cobalt by a solution of arscnijite of 

 potash ; and mix this precipitated arseniate of cobalt with six- 

 teen times as much moist alumine. 



4. Mix the nitric solution of cobalt or zaffre at once with fresh- 

 made alumine; this is of a good blue colour. 



5. Precipitate the nitric solution of cobalt or zaffVc with a 

 solution of ammonia alum ; this is j)aler than the rest. 



CHROMIUM. 



CiiROMATE OP IRON. Found In masses in the Shetland Isles, 



