in summer it may be only about 12 to 14 days, but in winter the longer period named is always required. At the end of the time the tubs are emptied and the grape refuse thrown away; the copper sheets are dried, then dipped into water, or, what is better, into bad wine (if that is obtainable), and again dried; by this means a coat of verdigris is formed on the plates, which is scraped off and placed on one side; the plates are redipped and again dried, when another coating of verdigris is formed, and scraped off as before; the process is repeated until all the copper has been converted into verdigris. The green is washed with water and then dried, when it is ready for use. At one time almost every vineyard in France and Belgium made verdigris somewhat on the above lines, although there were some variations in the minor details; but, as the consumption of verdigris has decreased considerably, its manufacture has not been so generally followed of late years.

2. English Process.-In England verdigris is made by packing plates of copper between cloths soaked in the crude pyroligneous acid obtained in the distillation of wood; this is done in casks; every four or five days the casks are unpacked and the cloths redipped in the acid, and the operation repeated until the sheets of copper begin to have a coat of verdigris; they are then dipped in water and dried; the verdigris on them is then scraped off and the copper is again packed with the cloths; and the process repeated until all the copper has been converted into verdigris, The refuse from the manufacture of cider has been used in making this pigment.

The verdigris is finished for use by washing and drying. The latter has to be done very carefully, as too high a temperature would affect the brilliancy of the tint.

Common verdigris is not quite so pure as distilled verdigris ; but as it is more insoluble in water and more opaque, it can be used as a pigment.

COMPOSITION AND PROPERTIES OF VERDIGRIS. -Phillips gives the following analysis of distilled verdigris :

Copper oxide, Cu O,

43.25 per cent.

28.45

Acetic anhydride, C, H, 0.0. C, H, O, 28-30
Water, H2O,

which corresponds to the formula

Cu 2 C2 H3 02, Cu H2 O2, 5 H2O.

:

Distilled verdigris is very constant in its composition. It forms dark green crystals somewhat soluble in water and in

acetic acid; heated in the air they lose their water of crystallisation and their acetic acid, and a black residue of copper oxide, Cu O, is left behind. Common verdigris is very variable in its composition and usually contains some impurities; as a rule, it is generally allowable for commercial verdigris to contain about 2 per cent.

The following analyses of some samples of common verdigris will show the average composition of this pigment:

1 is by Phillips of an English-made sample. 2 and 3 are by the author; the water in these was present both as hygroscopic and combined water-in No. 2 the amounts were respectively 7.95 and 10 05, in No. 3 they were 4:49 and 8.75. 4 and 5 are by Berzelius of French-made samples.

Verdigris has a greenish-blue colour. It makes but a poor pigment, being the most fugitive of the copper-greens; in water it soon fades, in oil it is rather more permanent, if kept free from moisture, which causes it to effloresce.

While being almost insoluble in water, it is readily soluble in all acids, without effervescence, to a blue solution, which gives the characteristic tests for copper. Heated with strong sulphuric

acid it evolves acetic acid. Heated alone it loses its water and acid and turns black, from the production of oxide of copper.

ASSAY AND ANALYSIS OF VERDIGRIS.—Verdigris may be assayed for tint, covering power, &c., in the usual

way.

The following impurities in verdigris should be tested for; Insoluble matter, carbonates, sulphates, and metals :

Insoluble Matter, which may consist of barytes, sand, &c., is readily tested for. A weighed quantity is treated with hot dilute hydrochloric acid for a short time and the insoluble matter collected on a filter, dried, and weighed. The amount of insoluble matter should not exceed 3 per cent., and even this is an excessive allowance, as can be inferred from the analyses already quoted; 2 per cent. is, in the opinion of the author, quite a sufficient allowance, and anything above this ought to be considered as an adulteration.

If, when treating with the acid, effervescence occurs it may be taken as an indication of the presence of carbonates either of copper or calcium, or both.

Sulphates can be tested for in the hydrochloric acid solution by adding barium chloride, and their amount may be determined by filtering off, drying, and weighing the precipitate of barium sulphate, which will be formed if they are present.

The presence of other metals than copper is best ascertained by working according to the following scheme. The pigment is heated to a red heat to decompose it, and the residue is dissolved in hydrochloric acid and any insoluble matter filtered off; through the solution a current of sulphuretted hydrogen is passed, to precipitate out the copper as the black sulphide; the filtrate is boiled down to a small bulk, a little strong nitric acid is added, and the mixture is boiled for a few minutes; ammonia is then added in slight excess; if any iron is present a reddishbrown precipitate will be obtained; this is filtered off and to the filtrate ammonium sulphide is added, which, if zinc is present, will throw down a white precipitate of the sulphide of zinc; after filtering this off, ammonium oxalate is added to the filtrate when, if calcium is present, a white precipitate of calcium oxalate will be obtained. Calcium may be present either in the form of carbonate or sulphate, which will be inferred from the results of other tests. It is rare for any other metal to be present.

Adulteration of verdigris with Prussian blue can be detected by the blue residue left after the treatment with acid giving all the reactions of Prussian blue. The addition of ultramarine is readily detected by the action of acid on the sample.

Green verditer is sometimes sold under the name of "British verdigris."

SCHEELE'S GREEN.

This pigment was discovered by Scheele, the eminent Swedish chemist, who communicated his method of making it to the Academy of Sciences of Stockholm in 1778. At first it was very much used, being at that time one of the best greens known, but the introduction of emerald-green in 1814 soon brought about its gradual disuse, and now it is doubtful whether it is ever used as a pigment; this is partly due to the fact that it is but a dull colour, while much brighter and better greens are now known; then, again, the fact of its being an arsenical colour has always been much against its use as a pigment.

PREPARATION OF SCHEELE'S GREEN.-1. Scheele gave the following instructions for preparing this green :-1 part of powdered white arsenic (arsenious oxide) and 2 parts of potash (carbonate of potassium) are dissolved, by boiling, in 35 parts of

water; the solution is filtered and then poured into a solution of 2 parts of copper sulphate as long as a precipitate falls. The precipitate is collected on a filter, washed with water, and dried at a gentle heat.

2. Parker patented, in 1812, a process of making Scheele's green-Two solutions were made in boiling water, one containing 16 ozs. of sulphate of copper, the other 14 drms. of arsenic and 14 ozs. of potash. The precipitate obtained on mixing the solutions was washed and dried. As the alkali is greatly in excess in this process, the precipitate must consist largely of carbonate of copper.

3. Sharples* prepares Scheele's green by dissolving 2 parts of arsenious oxide (white arsenic) in 8 parts of soda crystals by boiling with 10 parts of water; when dissolved, the arsenite of soda formed is poured into a solution of 6 parts of copper sulphate in 40 parts of water. Both solutions are mixed while boiling, and the mixture itself boiled for a few minutes; it is then allowed to stand until the next day, when the green supernatant liquor is poured off and the green washed two or three times with hot water, dried, and filtered. This is stated to be the most economical process of making the green.

4. Berzelius describes a process of preparing a green by boiling copper carbonate with white arsenic; the green has a fine tint. COMPOSITION AND PROPERTIES OF SCHEELE'S GREEN.-Scheele's green is essentially an arsenite of copper. Sharples, who has made a very exhaustive examination of this pigment, states that it is a basic arsenite of copper, usually containing small traces of carbonate and sulphate of copper. He gives the following as the composition of a pure Scheele's green:

The pigment as prepared on a commercial scale differs somewhat from this, as might be expected; but the variation is not very great when properly made. The following analyses given by Sharples of samples made by Scheele's and Berzelius' processes will show the average composition of this pigment :—

Sample 2 was made according to the original directions; but sample 3 was washed until the wash-waters were free from arsenic.

Scheele's green is of a pale yellowish-green colour, but not very bright; it is quite insoluble in water, but soluble in dilute acids, in dilute solutions of the caustic alkalies, and in ammonia with a blue colour; when boiled with solutions either of the caustic alkalies or of their carbonates it is decomposed, black oxide of copper being deposited; boiling with ammonia does not decompose it. When heated it decomposes, a residue of black oxide of copper being left behind and the arsenic being volatilised.

As a pigment it is not satisfactory; its covering power is small, although it can be used either for oil- or water-colours; it is not permanent and fades on exposure to light and air; in this respect it is rather better than any of the other copper-greens previously described. As a pigment it has gone out of use.

EMERALD-GREEN.

Emerald-green was discovered in 1814, but by whom has not been recorded; from the place at which it was supposed to have been first made it is also known as "Schweinfurth green"; while in America it is largely known as Paris green," under which name it is mostly consumed as an insecticide on fruit farms. Owing to the brilliancy of its tint, the ease with which it works, and its comparative permanence, it has been extensively used as a pigment. In composition it is an aceto-arsenite of copper, and may be regarded as a compound of verdigris and Scheele's green.

PREPARATION OF EMERALD-GREEN.—1. 125 lbs. of copper sulphate are dissolved in boiling water; 50 lbs. of white arsenic (arsenious oxide) are boiled with a solution of 130 lbs. of