To be mixed with water to a paste. It does not fuse nor act as a paste until exposed to great heat. Before applying it wash the edges to be united with liquid ammonia. Brimstone or sulphur melts iron very promptly when the latter is red-hot, and applied to it, the iron will drop like melted sealing-wax.
A cement for iron stoves is made as follows:—
| Iron filings | 100 |
| Chalk-marl | 40 |
| Flint-sand | 50 |
| Vinegar | 20 |
This is made into a paste, which can be rendered porous by mixing with it bristles, chopped straw, sawdust, or chaff. When the latter is converted to coal by heat, the cement is, of course, full of cavities. In like manner, clay for water-coolers is made light and spongy by mixing it with salt. The salt gradually melts in the damp clay, forming a porous substance.
When iron doors are to be hermetically sealed at very high temperatures the following may be used:—
| Finest iron filings | 100 |
| Sal-ammoniac | 1 |
| Limestone | 10 |
| Silicate of soda | 10 |
When the iron plates about a fireplace give way the following may be used:—
| Iron filings | 20 |
| Iron dross or refuse | 12 |
| Calcined gypsum | 30 |
| Common salt | 10 |
This mixture may be combined with either blood or silicate of soda, preferably the latter, as the former has a disagreeable smell.
Iron filings mixed with vinegar are allowed to stand till of a brown colour, and then driven with plugs and hammer into cavities, where they form a rust cement.