A piece of zinc will displace the iron in like manner, leaving a solution of nitrate of zinc.
Nearly all the colours used in the arts are produced by metals and their combinations; indeed, one is named chromium, from a Greek word signifying colour, on account of the beautiful tints obtained from its various combinations with oxygen and the other metals. All the various tints of green, orange, yellow, and red, are obtained from this metal.
Solutions of most of the metallic salts give precipitates with solutions of alkalies and their salts, as well as with many other substances, such as what are usually called prussiate of potash, hydro-sulphuret of ammonia, &c.; and the colours differ according to the metal employed, and so small a quantity is required to produce the colour that the solutions before mixing may be nearly colourless.
EXPERIMENTS.
1. To a solution of sulphate of iron add a drop or two of a solution of prussiate of potash, and a blue colour will be produced.
2. Substitute sulphate of copper for iron, and the colour will be a rich brown.
3. Another blue, of quite a different tint, may be produced by letting a few drops of a solution of ammonia fall into one of sulphate of copper—a precipitate of a light blue falls down, which is dissolved by an additional quantity of the ammonia, and forms a transparent solution of the most splendid rich blue colour.
4. Into a solution of sulphate of iron let fall a few drops of a strong infusion of galls, and the colour will become a bluish-black—in fact, ink. A little tea will answer as well as the infusion of galls. This is the reason why certain stuffs formerly in general use for dressing gowns for gentlemen were so objectionable; for as they were indebted to a salt of iron for their colour, buff as it was called, a drop of tea accidentally spilt produced all the effect of a drop of ink.
5. Put into a largish test tube two or three small pieces of granulated zinc, fill it about one-third full of water, put in a few grains of iodine and boil the water, which will at first acquire a dark purple colour, gradually fading as the iodine combines with the zinc. Add a little more iodine from time to time, until the zinc is nearly all dissolved. If a few drops of this solution be added to an equally colourless solution of corrosive sublimate (a salt of mercury) a precipitate will take place of a splendid scarlet colour, brighter if possible than vermilion, which is also a preparation of mercury.