There have been a great number of compounds or mixtures proposed for fire proofing wood, fabrics, and other inflammable materials. Among the best of these may be mentioned ammonium chloride, ammonium phosphate, ammonium sulphate, alum, borax, boric acid, calcium chloride, magnesium chloride, sodium silicate, sodium tungstate, stannous chloride, and aluminium hydroxide. Any of these may be applied in solutions of 5 to 10 per cent. strength, except the last; aluminium hydroxide is formed as an insoluble substance in the fibre by soaking first in aluminium sulphate solution and afterwards in ammonia. Alum is very often used, and by some sodium tungstate is considered the best preventive of fire. A good mixture is ammonium chloride 15 parts, boric acid 6 parts, borax 3 parts, and water 100 parts, heated to boiling, and the wood or fibre plunged into it.