IRON A GABBIER OF OXYGEN 253 



ferricyanide, a precipitate dark-blue from the first, Fe 4 [Fe 



The ferric salts are oxidising agents, are mostly brown or 

 red, and in solution exhibit, with hydrochloric acid, a nega- 

 tive reaction ; with sulphuretted hydrogen, give a white 

 precipitate of sulphur ; with ammonium hydrosulphide, the 

 black ferrous sulphide, together with sulphur ; with caustic 

 alkalies, a brown-red precipitate of ferric hydrate ; with 

 potassium ferrocyanide, a deep-blue precipitate of Prussian 

 blue, at once goes down ; with potassium ferricyanide, no 

 precipitate, but an olive or brown discoloration ; with 

 solution of galls, neutral solutions yield a blue-black pre- 

 cipitate the basis of writing ink ; with potassium sulpho- 

 cyanide, an intense blood-red colour. 



ACTIONS AND USES. Iron and its salts were the first 

 mineral substances employed in medicine ; they have been 

 used for three thousand years ; but although anciently and 

 extensively prescribed, a good deal has still to be learned 

 regarding them. 



The presence of iron seems to be essential to life of practi- 

 cally all forms of protoplasm. In the bodies of the higher 

 animals iron occurs chiefly in the blood. About 9 grammes is 

 obtained from the blood of a horse or ox of about 1000 Ibs. 

 live- weight. In the haemoglobin and oxy haemoglobin the 

 iron performs much the same functions as it does in the 

 ferrous and ferric oxides in the soils. In the lungs, haemo- 

 globin takes up oxygen, and becomes oxyhaemoglobin, which 

 readily parts with oxygen as it circulates through the 

 capillary vessels. Thus maintaining the healthy activity of 

 these blood constituents, iron is said to act as a haematinic or 

 blood tonic. Its curative effects are specially manifested in 

 anaemia, in which the number of red corpuscles and amount 

 of haemoglobin are seriously reduced, sometimes to the 

 amount of one-fifth of their normal proportion, impairing 

 tissue oxidation and functional activity. In chlorosis, 

 where there is a deficiency of haemoglobin but a normal 

 number of red cells, it is especially valuable. Clinical 

 observation testifies that full doses of iron restore the pallid 

 soft textures to their normal colour and firmness, and im- 

 prove general health. These curative results depend upon 



