(See also Metals and Steel.)

To Color Iron Blue

One hundred and forty parts of hyposulphite of soda are dissolved in 1,000 parts of water; 35 parts of acetate of lead are dissolved in 1,000 parts of water; the two solutions are mixed, boiled, and the iron is immersed therein. The metal takes a blue color, such as is obtained by heating.

To Distinguish Iron from Steel

The piece of metal to be tested is washed and then plunged into a solution of bichromate of potash, with the addition of considerable sulphuric acid. In half a minute or a minute the metal can be taken out, washed, and wiped. Soft steels and cast iron assume under this treatment an ash-gray tint. Tempered steels become almost black, without any metallic reflection. Puddled and refined irons remain nearly white and always have metallic reflections on the part of their surface previously filed, the remainder of the surface presenting irregular blackish spots.

Another method is to apply a magnet. Steel responds much more quickly and actively to the magnetic influence than does iron.

Powder for Hardening Iron and Steel

For wrought iron place in the charge 20 parts, by weight, of common salt; 2 parts, by weight, of potassium cyanide; 0.3 parts, by weight, of potassium bi-

chromate; 0.15 parts, by weight, of broken glass; and 0.1 part, by weight, of potassium nitrate for case-hardening. For cooling and hardening cast iron: To 60 parts, by weight, of water add 2.5 parts, by weight, of vinegar; 3 parts, by weight, of common salt; and 0.25 parts, by weight, of hydrochloric acid.

Preventing the Peeling of Coatings for Iron

To obviate the scaling of coatings on iron, if exposed to the attacks of the weather, it is advisable to wash the iron thoroughly and to paint it next with a layer of boiling linseed oil. If thus treated, the paint never cracks off. If the iron objects are small and can be heated, it is advantageous to heat them previously and to dip them into linseed oil. The boiling oil enters all the pores of the metal and drives out the moisture. The coating adheres so firmly that frost, rain, nor wind can injure it.

To Soften Iron Castings

To soften hard iron castings, heat the object to a high temperature, cover it over with fine coal dust or some similar substance, and allow it to cool gradually. When the articles are of small size, a number of them are packed in a crucible with substances yielding carbon to iron at a glowing heat. The crucible is then tightly closed, and placed in a stove or on an open fire. It is gradually heated and kept at a red heat for several hours, and then allowed to cool slowly. Cast-iron turnings, carbonate of soda, and unrefined sugar are recommended as substances suitable for packing in the crucible with the castings. If unrefined sugar alone is added, the quantity must not be too small. By this process the iron may be rendered extremely soft.

To Whiten Iron

Mix ammoniacal salt in powder with an equal volume of mercury. This is dissolved in cold water and mixed thoroughly. Immerse the metal, heated to redness, in this bath and it will come out possessing the whiteness and beauty of silver. Care should be taken not to overheat the article and thus burn it.


See Pyrotechnics.


See Adhesives.


See Cleaning Preparations and Methods.


See Adhesives.


See Adhesives, under Rubber Cements.


See Photography.