The sale of arsenic and its preparations to the public is properly hedged round with restrictions of all kinds. No arsenic may be sold to a person under age, nor may it be sold unless mixed with soot or indigo in the proportion of 1 ounce of soot or 1/2 ounce of indigo at the least to every pound of arsenic. When damp, Ferro-silicon evolves AsH and PH , both very lethal gases.

Steel, the strongest of all forms of iron, is an alloy of iron and carbon, and for various purposes these are further mixed with nickel and silicas. Many other alloys have been discovered within the last few years, and each makes possible new uses for iron requiring greater strength. One of the best of these is a mixture of iron and silicon, called ferro-silicon.