Popular Science Monthly 



Manufacturing Prussian Blue from 

 American Products 



THE shortage of many colors and dye- 

 stuffs in the United States since 

 the European war has caused a thorough 

 investigation into the means available 

 for the direct manufacture of Prussian 

 blue, which has been and still is in great 

 demand for the production of printers' ink, 

 dyeing, wall-paper printing, oil color and 

 in compounding colors for many other uses 

 where an intense blue is required. Prussian 

 blue, or cyanide of iron, has hitherto been 

 produced mainly from the potassium salts, 

 such as the cyanide and ferro-cyanide, and 

 known in trade as soluble Prussian blue 

 represented by the symbols KFE2 (CN)6, 

 while the insoluble blue is represented by 

 FE7 (CN)i8 and FE5 (CN)i2. 



The great demand for this blue coupled 

 with the increasing scarcity of it has 

 caused the price to rise considerably. The 

 production of this valuable color from the 

 potassium salts is out of the question in the 

 United States. This is because the supply 

 of salts from the European market has 

 ceased, and those obtainable are too costly. 

 However, cyanide blue can be made at a 

 very moderate cost from the following ma- 

 terials to be procured in the United States: 

 Sulphuric acid, 66 deg., nitric acid, 38 or 

 42 deg., proto-sulphate of iron (common 

 copperas) and a product known as cyanide 

 mixture, which consists of a combination of 

 cyanide of sodium, and chloride of sodium, 

 which will yield from 39.2 to 40 per cent 

 of cyanogen. The sulphuric acid and 

 nitric acid are of the commercial variety, 

 not necessarily chemically pure. 



A number of wine barrels will be required 

 of a capacity of 50 or 60 gal. each, which 

 have been dried and thoroughly coated on 

 the inside with very hot, hard paraffin. 

 The barrels are for use in producing and 

 holding a saturated solution of proto- 

 sulphate of iron called the copperas solu- 

 tion, which is made by impending about 

 100 lb. of the iron salt in small sacks 

 attached by nailing to a simple wood frame 

 made so that the ends of the frame rest 

 upon the top of the barrel. The sack or 

 bag when suspended should occupy about 

 two-thirds the depth of the interior. By 

 this means the sack hangs in the water and 

 must not occupy more than three-quarters 

 of the space within, because the constant 

 dissolving of the iron salt will gradually 

 fill the barrel. As the salt dissolves, a 



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quantity of dirt will be held in the sack 

 while a completely saturated solution will 

 occupy the lower portion of the barrel. 

 The barrel should be provided with a wood 

 stop cock well soaked in hot paraffin placed 

 about 6 in. from the bottom. This will 

 allow for the saturated solution to be 

 drawn off clear and free from dirt. The 

 sacks or bags must be kept full to the brim 



A sack or bag to hold the iron salt is 

 hung from a square frame in a barrel 



with the iron salt, which is readily accom- 

 plished by the use of an iron pail. The 

 cyanide solution must also be prepared 

 for use by employing a clean sack in a 

 barrel of water the same as for the iron 

 salt. In this case about 157 lb. of the 

 cyanide mixture will give 50 gal. of a 

 saturated solution, approximately, much 

 depending on the temperature. 



The concentrated solution of cyanide 

 should register on the hydrometer 100 

 grains to the ounce of water. A Baume 

 hydrometer will be required to test the 

 iron solution, which should register 30 or 

 31 when ready for use. This will be equal 

 to about 100 or 110 grains of iron salt to 

 each ounce of water. Several large stone- 

 ware crocks will be required of a capacity 

 from 30 to 50 gal. in which the saturated 

 solution of iron salt is oxidized under heat 

 and acid. This is carried out in the follow- 

 ing manner: 



Oxidizing the Iron Solution 



Place 30 gal. of the saturated solution 



into a 50-gal. crock and pour into it 6 pints 



of sulphuric acid, 66 deg. Stir the mixture 



well and heat it with steam, using a pressure 



