304 CHAPTER XXII. 



of iron in distilled water, and pour it gradually into a con- 

 centrated solution of yellow prussiate of potash. There is 

 produced a precipitate of insoluble Prussian blue. (An 

 excess of prussiate of potash ought to remain in the liquid ; 

 in order to ascertain whether this is the case take a small 

 quantity of the liquid and observe whether a drop of sulphate 

 of iron still precipitates it.) Filter the liquid through a felt 

 strainer, underneath which is arranged a paper filter in a 

 glass funnel. The liquid at first runs clear and yellowish 

 into the lower funnel ; distilled water is then poured little by 

 little on to the strainer ; gradually the liquid issuing from 

 the strainer acquires a blue tinge, which, however, is not 

 visible in that which issues from the lower filter. Distilled 

 water is continually added to the strainer for some days until 

 the liquid begins to run off blue from the second filter. 

 The Prussian blue has now become soluble. The strainer 

 is turned inside out and agitated in distilled water ; the 

 Prussian blue will dissolve if the quantity of water be suffi- 

 cient. 



The solution may now be injected just as it is, or it may 

 be kept in bottles till wanted, or the solution may be 

 evaporated in a stove, and the solid residuum put away in 

 bottle. 



For injections, if a simple aqueous solution be taken, 

 it should be saturated. Such a mass never transudes 

 through the walls of vessels. Or it may be combined with 

 one fourth of glycerin, or with the gelatin vehicle above 

 described. 



491. BRUCKE'S Soluble Berlin Blue (Arch. f. mik. Anat., 1865, 

 p. 87). 



Make a solution of ferrocyanide of potassium containing 217 

 grammes of the salt to 1 litre of water. 



Make a solution of 1 part commercial chloride of iron in 

 10 parts water. 



Take equal volumes of each, and add to each of them 

 twice its volume of a cold saturated solution of sulphate of 

 soda. Pour the chloride solution into the ferrocyanide solu- 

 tion, stirring continually. Wash the precipitate on a filter 

 until soluble, dry it, press between blotting-paper in a press, 

 break the mass in pieces, and dry in the air. 



