3. Action on Metals.—Gently heated in a test tube with copper filings, orange-coloured fumes are given off, which redden but do not bleach litmus paper. Starch paper treated with iodide of potassium becomes purple.
4. Solution of Gold.—If a small portion of gold leaf be put into the acid, no effect is produced; but on the addition of concentrated hydrochloric acid, the metal is rapidly dissolved.
II. Dilute Acid
1. Absence of sulphuric and hydrochloric acids, proved by no precipitate being formed with nitrate of barium and nitrate of silver.
2. It does not char paper when the paper is heated, as is the case with sulphuric and hydrochloric acids.
3. If a piece of filtering paper be dipped into a solution of the acid saturated with carbonate of potash, dried and ignited, it will burn like touch-paper.
4. The acid liquid, saturated with carbonate of potash and evaporated, deposits fluted prisms which do not effloresce or deliquesce on exposure. Neutralised with soda, the crystals are of a rhombic form.
5. A crystal, so formed, moistened with distilled water on a plate, and then heated with strong sulphuric acid and allowed to cool, gives with—
(1) A piece of green sulphate of iron—a dark green ring round the crystal.
(2) A small portion of morphia—a rich orange colour, a yellow liquid being formed.