BRUOKE'S SOLUBLE BERLIN BLUE. 267 



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 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. 



477. Soluble Prussian Blue (GUIGNET, 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 precipitate 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. 



478. Briicke's Soluble Berlin Blue (Arch. f. mik.Anat., 1865, 

 p. 87). Briicke first prepared it by taking a 10 per cent, 

 solution of ferrocyanide of potassium, and precipitating by 



