BRUUKE S SOLUBLE BERLIN BLUE. 225 



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 ac- 

 quires 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 sufficient. 



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 bottles. 



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. 



450. Soluble Prussian Blue ((TUIGNET, Journ. de Microgr., 

 1889, p. 94; Journ. Roy. Mic. Soc., 1889, p. 468). Guignet 

 gives two methods : 



1. To a boiling solution of 110 grammes of ferridcyanide of 

 potassium, are added gradually 70 grammes of crystallised 

 sulphate of iron. After boiling two hours it is filtered, and 

 the filtrate washed with fresh water until the washings are 

 strongly blue. It is then dried at 100 C. 



2. A saturated solution of oxalic acid is mixed to a pasty 

 consistence with an excess of pure Prussian blue. The liquid 

 is filtered and allowed to stand for two months until all the 

 blue is precipitated. It is then filtered and washed with weak 

 spirit in order to remove any oxalic acid, then dried. 



A similar result may be at once obtained by precipitating 

 the oxalic solution with 95 per cent, alcohol, or with a con 

 centrated solution of sodium sulphate, and then washing the 

 precipitate with weak spirit. 



451. Briicke's soluble Berlin Blue (Arch. f. mik. Anat., 1865, 



15 



