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PK00FS OF THE PROPERTIES OF COPPER.

Then take a warm solution of sulphate of copper and pour it intothe arseniate of potash; a little only must be added at a time,and it must be continually stirred with a glass rod. Leave themixture at rest till a precipitate is formed; then decant the li-quor, and having washed the residuum repeatedly in watmwater, filter it and leave it to dry. By this process a beautifulgreen colour is obtained.

As this colour is not alterable by air, it is employed inpainting.

Experiment VIII.

Preparation of Hue verditer.

To a solution of nitrate of copper, add pulverized lime, andshake the mixture to facilitate the decomposition, A little ex-cess of nitrate of copper should be used, that the whole of thelime may be saturated, and that the precipitation formed at themoment of mixture may be a pure precipitation of copper; theprecipitate is suffered to settle, after which the super-natantfluid is decanted, and the residuum being repeatedly washed, isdeposited on a piece of cloth to drain.

It is from this precipitate, which is of a delicate green colour,that the blue verditer is prepared.

For this purpose grind it on a colour-stone or in a largemortar with a little quick-lime. This mixture acquires, in amoment, by trituration a very' lively blue colour. The quantityof lime necessary is about four or five percent, of the precipitate.

If the precipitate is too dry, add a very small quantity ofwater, in order that the mixture may form a paste somewhatliquid, and easy to be pounded.

The whole must be afterwards dried.

Remark. ..There are two kinds of verditer in the market;the one, called refiners verditer, has the form of a very soft, im-palpable powder, and possesses a stronger body of colour thanthe other, which is in harsh, irregular lumps, not easily diffu-sible in water.