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
��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