268 INJECTIONS. 



means of a dilute solution of sesquichloride of iron (taken in 

 such a quantity as to contain just half as much chlorine as is 

 necessary for the decomposition), and washing the precipitate 

 on the filter until solubility is attained. 



Later on he employed a greater excess of ferrocyanide, and 

 took just so much dilute solution of chloride of iron that the 

 weight of the dry chloride employed came to y 1 ^ or -J- of 

 that of the ferrocyanide. The precipitate was washed on a 

 filter (using the filtrate to wash with) until nothing but a 

 clear yellow liquid filtered off, then washed with water until 

 the water began to run off blue, then dried, pressed between 

 blotting-paper in a press, the resulting mass broken in pieces 

 and dried by exposure to the air. 



A cheaper method is the following : 



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 solution, 

 stirring continually. Wash the precipitate on a filter until 

 soluble, and treat as above described. 



The concentrated solution of the colouring matter is to be 

 gelatinised with just so much gelatin that the mass forms a 

 jelly when cold. 



479. Thiersch's Prussian Blue Gelatin Mass (Arch. f. mik. 

 Anat., i, 1865, p. 148). 

 Take 



(1) A solution of 1 part gelatin in 2 parts water. 



(2) A saturated aqueous solution of sulphate of iron. 



(3) A saturated aqueous solution of red prussiate of 

 potash. 



(4) A saturated aqueous solution of oxalic acid. 



Now (A) mix 12 c.c. of the iron solution with one ounce of 

 the gelatin solution at the temperature of 25 R. 



Then (B) mix, at the same temperature, 24 c.c. of the prus- 

 siate solution with two ounces of the gelatin solution. 



(c) To the latter mixture add first 24 c.c. of the oxalic 

 acid solution, stir well, and then add the gelatin and iron 



