hands of those engaged in gilding or plating are subjected to ulceration, particularly if they have been immersed in the solution. The ulcers are not only annoying but painful; and, on their first appearance, if care is not properly taken to wash them in strong cyanide of potassium, and then in acid water, the operator will, in a short time, have to take a few days rest. We have repeatedly seen, by the aid of a magnifying glass, gold and silver reduced in these ulcerations. We have also known of eruptions breaking out over the bodies of workmen after inhaling those deleterious fumes when they were very bad, as when solutions were precipitated by acids or being evaporated to dryness in a close apartment for the recovery of the metal. Repeatedly have we seen the legs of workmen thus afflicted, and always after they have been exposed to extra fumes.

The following statement of the general effects of electro-plating and gilding on the health of those engaged in them, as experienced by ourselves and others, may not be uninteresting to our readers: but it is necessary to premise that the apartments in which we were employed were improperly ventilated.

The gas has a heavy sickening smell, and gives to the mouth a saline taste, and scarcity of saliva; the saliva secreted is frothy. The nose becomes dry and itchy, and small pimples are found within the nostrils, which are very painful (we have felt these effects in the nose from the hydrogen of the batteries, where there were no cyanide solutions). Then follows a general languor of body; disinclination to take food, and a want of relish. After being in this state for some time, there follows a benumbing sensation in the head, with pains, not acute, shooting along the brow; the head feels as a heavy mass, without any individuality in its operations. Then there is bleeding at the nose in the mornings when newly out of bed; after that comes giddiness; objects are seen flitting before the eyes, and momentary feelings as of the earth lifting up, and then leaving the feet, so as to cause a stagger. This is accompanied with feelings of terror, gloomy apprehension, and irritability of temper. Then follows a rushing of blood to the head; the rush is felt behind the ears with a kind of hissing noise, causing severe pain and blindness: this passes off in a few seconds, leaving a giddiness which lasts for several minutes. In our own case the rushing of blood was without pain, but attended with instant blindness, and then followed with giddiness. For months afterwards a dimness remained as if a mist intervened between us and the objects looked at: it was always worse towards evening, when we grew very languid and inclined to sleep. We rose comparatively well in the morning: yet were restless, our stomach was acid, visage pale, features sharp, eyes sunk in the head, and round them dark in color: these effects were slowly developed. Our experience was nearly three years.

We have been thus particular in detailing these effects, as a warning to all employed in the process; but we have no doubt that

in lofty rooms, airy and well ventilated, these effects would not be felt. Employers would do well to look to this matter; and amateurs, who only use a small solution in a tumbler, should not, as the custom sometimes is, keep it in their bed-rooms; the practice is decidedly dangerous.

PRACTICAL SUGGESTIONS IN GILDING.-According to the amount of gold deposited, so will be its durability: a few grains will serve to give a gold color to a very large surface, but it will not last: this proves, however, that the process may be used for the most inferior quality of gilding. Gold thinly laid upon silver will be of a light color, because of the property of gold to transmit light. The solution for gilding silver should be made very hot, but for copper it should be at its minimum heat. A mere blush may be sufficient for articles not subjected to wear; but on watch-cases, pencil-cases, chains, and the like, a good coating should be given. An ordinary sized watch-case should have from 20 grains to a pennyweight; a mere coloring will be sufficient for the inside, but the outside should have as much as possible. A watch-case thus gilt, for ordinary wear, will last five or six years without becoming bare. We have known some to be in use full six years without losing their covering. Small silver chains, such as those sold at eight shillings, should have 12 grains; pencil-cases, of ordinary size should have from 3 to 5 grains; a thimble from 1 to 2 grains. These suggestions will serve as a guide to amateur gilders, many of whom, having imparted only a color to their pencil-cases, feel chagrin and disappointment upon seeing them speedily become bare; hence arises much of the obloquy thrown upon the process.

CHAPTER XXXII.

RESULTS OF EXPERIMENTS ON THE DEPOSITION ON OTHER METALS AS COATINGS.

COATING WITH PLATINUM.-This metal has never yet been successfully deposited as a protecting coating to other metals. A solution may be made by dissolving it in a mixture of nitric and muriatic acids, the same as is employed in dissolving gold; but heat must be applied. The solution is then evaporated to dryness, and to the remaining mass is added a solution of cyanide of potassium; next, it must be slightly heated for a short time, and then filtered This solution, evaporated, yields beautiful crystals of cyanide of platinum and potassium; but it is unnecessary to crystallize the salt. A very weak battery power is required to deposit the metal: the solution should be heated to 100°. Great care must be taken to obtain a fine metallic deposit: indeed the operator may not sue

ceed once in twenty times in. getting more than a mere coloring of metal over the surface, and that not very adhesive. The causes of the difficulty are probably these: the platinum used as an electrode is not acted upon; the quantity of salt in solution is very little; it requires a particular battery strength to gives a good deposit, and the slightest strength beyond this gives a black deposit; so that, were the proper relations obtained, whenever there is any deposit, the relations of battery and solution are changed, and the black pulverulent deposit follows.

We have occasionally succeeded in obtaining a bright metallic deposit of platinum, possessing the qualities of adhesion and durability: some of the articles thus covered presented no signs of change after many years: but we have never been so fortunate as to get a platinum deposit that could protect any metal from the action of acids, or other fluids by which the metal could be affected. We have covered iron, such as the end of a glass-blower's blowpipe, so that it could be made red-hot without the iron rusting, but rather taking the characteristic appearance of platinum: but even that did not protect the iron from rusting when it was put a short time into water, or kept exposed to moist air. We have seen again and again recommendations of certain solutions of platinum for the purpose of obtaining a reguline metal, and no doubt it has been obtained, but, as stated above, we believe more incidentally than at will. The protoxalate of platinum has been strongly recommended for covering copper and brass with platinum.*

COATING WITH PALLADIUM.-Palladium is a metal very easily deposited. The solution is prepared by dissolving the metal in nitro-muriatic acid, and evaporating the solution nearly to dry. ness; then adding cyanide of potassium till the whole is dissolved: the solution is then filtered and ready for use. The cyanide of potassium holds a large quantity of this metal in solution, and the electrode is acted upon while the deposit is proceeding. Articles covered with this metal assume the appearance of the metal; but so far as we are aware, it has not yet been applied to any practical purpose. It requires rather a thick deposit to protect metals from the action of acids, which is, probably, the only use it can be applied to.

COATING WITH NICKEL.-Nickel is very easily deposited; and may be prepared for this purpose by dissolving it in nitric acid, then adding cyanide of potassium to precipitate the metal; after which the precipitate is washed and dissolved by the addition of more cyanide of potassium. Or the nitrate solution may be precipitated by carbonate of potash; this should be well washed, and then dissolved in cyanide of potassium; a proportion of carbonate of potash will be in the solution, which we have not found to be detrimental. This latter method of preparing the nickel plating solution is simple, and, therefore, has our recommendation. The

* Polytechni. Constah. 1855.

metal is very easily deposited; it yields a color approaching to silver, which is not liable to tarnish on exposure to the air. A coating of this metal would be very useful for covering common work such as gasaliers, and other gas-fittings, and even common plate. The great difficulty experienced is to obtain a positive electrode: the metal is very difficult to fuse, and so brittle that we have never been able to obtain either a plate or a sheet of it. Could this difficulty be easily overcome, the application of nickel to the coating of other metals would be extensive, and the property of not being liable to tarnish would make it eminently useful for all general purposes. We coated articles with nickel in 1845, which were exposed to the air for many years without tarnish, and when last seen by the author exhibited no change.

ANTIMONY, ARSENIC, TIN, IRON, LEAD, BISMUTH, AND CADMIUM. -We have deposited these metals from their solutions in cyanide of potassium; but not for any useful application.

IRON.-Iron may be very easily deposited from its sulphate: dissolve a little crystalline sulphate of iron in water, and add a few drops of sulphuric acid to the solution: one pair of Smee's battery may be used to deposit the iron upon copper or brass. The metal in this pure state has a very bright and beautiful silver color.

LEAD.-Lead may be deposited from a solution of an acid salt, such as the acetate, but requires some management or strength of battery: it may also be deposited from its solution in potash or soda.

ALUMINIUM AND SILICIUM.-Since the publication of the former edition of this work, new methods have been discovered for obtaining the base or metal of alumina and silica, or clay and sand, in the metallic state possessing extraordinary properties. One of the methods successfully adopted, is by fusing in a small crucible some chloride or fluoride of aluminium, and when in fusion, inserting two steel poles in connection with a battery which reduces the salt, giving small globules of the metal aluminium.

Attempts have also been made to deposit the metals from their cyanous solution as coating upon other metals in the usual way. We have not ourselves tried any experiments upon these metals, but we take the following results of experiments from Mr. G. Gore of Birmingham, who seems to have given the subject a good deal of attention:

"It has long been known to chemists that all kinds of clay, stone, and sand, of which the earth is composed, consist of metais combined with oxygen, carbonic acid, sulphuric acid, and other non-metallic elements, forming therewith oxides, carbonates, sulphates, etc.; thus clay is an oxide of aluminium, sand an oxide of silicium, limestone a carbonate of calcium; but the separation of the metallic bases from the non-metallic elements with which they are combined has been a matter of so great difficulty, that few chemists have put themselves to the trouble of accomplishing it, and those who have done so have made use of the most powerful means and

reducing agents, such as large voltaic batteries, potassium, etc, and have then obtained them in a state of alloy or combination with mercury. Sir Humphrey Davy, the discoverer of most of these bases, in his experiments on the decomposition of the alkalies and earths, used a powerful battery, consisting of 500 pairs of plates, and then succeeded in obtaining them combined with mercury, from which they were afterwards separated. Wöhler and Berzelius, in their discoveries of the means of separating the metals aluminium and silicium from their respective compounds, clay and sand, used a high temperature and potassium, and then succeeded in obtaining them in the condition of dull metallic powders, nearly infusible.

"By a means recently discovered, and described in the March number of the Philosophical Magazine for this year, I have succeeded in depositing the metals aluminium from clay, and silicium from sandstone, each in a perfect metallic condition, by dissolving pipe clay, common red sand, pounded stone, etc., in various chemical liquids, and passing currents of electricity from ordinary small voltaic batteries through the solutions.

My attention has since been directed to produce simple processes, whereby any person not possessing a knowledge of chemistry may readily coat articles with those metals, and thus cause the discovery to be immediately applied to human benefit in the arts and manufactures, and the following are the results of my experiments:

"To coat articles of copper, brass, or German silver, with aluminium, take equal measures of sulphuric acid and water, or take one measure each of sulphuric and hydrochloric acids and two measures of water; add to the water a small quantity of pipe-clay, in the proportion of 5 or 10 grs. by weight to every ounce by measure of water (or oz. to the pint): rub the clay with the water until the two are perfectly mixed, then add the acid to the clay solution, and boil the mixture in a covered glass vessel one hour. Allow the liquid to settle, take the clear, supernatant solution, while hot, and immerse in it an earthen porous cell, containing a mixture of one measure of sulphuric acid and ten measures of water, together with a rod or plate of amalgamated zine; take a small Smee's battery, of three or four pairs of plates, connected together intensity fashion, and connect its positive pole by a wire, with a piece of zinc in the porous cell. Having perfectly cleaned the surface of the article to be coated, connect it by a wire with the negative pole of the battery, and immerse it in the hot clay solution; immediately abundance of gas will be evolved from the whole of the immersed surface of the article, and in a few minutes, if the size of the article is adapted to the quantity of the current of electricity passing through it, a fine white deposit of aluminium will appear all over the surface. It may then be taken out, washed quickly in clean water, and wiped dry, and polished; but if a thicker coating is required, it must be taken out when the deposit