TO PREPARE CHLORATE OF

POTASH.

THE variety of uses to which this salt is now put, particularly in making those matches which we import apparently in such large quantities from France, induces us to transcribe, from a French work, an account of the method of manufacturing it. A convenient number of coarse earthenware retorts, containing peroxide of manganese reduced to coarse powder, are placed over and around a furnace, as seen in the plate. Each of them has a crooked tube adapted to it, and is placed in communication with a Woolf's flask by means of another tube bent at right angles; and water is put in the flask in order that the passage of the gas may be seen. There is an upright tube of safety, which also reaches a little under the surface of the water in each flask; and a third tube, which does not descend to the water, connects it with the vessel containing the potash. This tube is of large diameter, having its two legs of unequal length; the shortest goes into the flask, and the longest plunges into a large vessel, generally of stone or common glass, containing subcarbonate of potash. A long and very small glass rod, bent somewhat like a hook, passes through the cork of the large bottle, and is made to fit as tight as is consistent with moving. The bent end enters the end of the tube, and the purpose of it is to keep the latter clear of crystals, which are apt to form at its mouth and stop it up. This is the reason, too, why it must be of a considerable diameter. Generally the solution of subcarbonate is made of American potash, which is purified as much as possible, by allowing it to remain for some days in earthen vessels before using it; and it should be concentrated from 30 to 35, according to the temperature of the season, After the apparatus has been made ready, and the joinings carefully luted, a quantity of muriatic acid is poured alternately into every retort, which is

repeated when chlorine ceases to come over; and this is continued till all the acid is consumed the operator chooses to employ. As the quantity of chlorine necessary to saturate the potash employed is known pretty accurately, the two are proportioned to one another by the operator, and he pours no more muriatic acid into the retort than will produce chlorine enough to answer this purpose. When all the acid has been added, and the gas has nearly ceased to pass over, heat is applied, but very gradually, and without interruption, till it is perceived that vapour and not chlorine comes over. This is known by the high temperature acquired by the tubes of communication, and by the liquid in the Woolf's bottle being discoloured and augmented in quantity. During the operation care must be taken to keep the tubes clear of obstruction, and to notice the height of the liquid in the safety-tubes, or the operator, in addition to other evils, will be much incommoded by the emission of chlorine. The alkaline solution, into which the chlorine is conveyed, grows at first thick, owing to the silica contained in the potash, which is precipitated as the saturation is effected; afterwards an effervescence takes place, which increases as the operation is continued, and crystals of chlorate of potash are deposited in brilliant scales. It should be observed, that in some places the solution of potash is filtered after the operation has been begun, in order to separate the silica, which is almost wholly deposited at the commencement. This, however, is an inconvenient method, and in general it is better to wait till the operation is over; when, after having allowed the chlorate and the silica to drain well, boiling water is poured on them, which dissolves the salt and leaves the silica. It is then filtered, and the chlorate crystallizes as the water cools. This is the salt the French use to make what they call oxygenated matches; and the process they employ we shall describe in our next. At

present we mean only to observe, that this salt has the property, when mixed with combustibles, of decomposing them with a violent detonation. On this account, Berthollet, the discoverer of it, proposed to use it in making a gunpowder, and a manufactory was begun at Essonne, in France; but the very first attempt at making it cost two persons their lives, the project was immediately abandoned, and has never since been revived. We mention this quality of the chlorate that our readers may be cautious how they employ it. It may also be mentioned, that this salt forms the basis of Mr. Forsyth's percussion powder, which is now employed as priming for fowling-pieces. THE INFALLIBLE BAROMETER.

To the Editor of the Chemist. SIR,-In No. XVII, of your excellent Work is an account of an infallible barometer, and without giving it the least thought, I went to purchase some chloride of ammonia; and when I arrived at Plough-court, I was informed that no such composition as chloride of ammonia could be formed; for by attempting to unite its bases, decomposition would take place. There is chlorate of ammonia and

hydrochlorate; and I presume, that it is the hydrochlorate that is meant, or, to speak in plainer terms, muriate of ammonia, or sal ammoniac. By the insertion of the above you will much oblige,

Yours truly, Potter's-fields, Horsleydown.

T. P.

The Article to which this alludes was taken without much attention from a French journal, which took it from an American scientific journal, into which it had probably been copied from the Mechanic's Magazine, where it appeared, we find, several months ago, and where it was also several months ago proved to be very erroneous. We confess we were caught by the title, not reflecting that claims to infallibility might be in barometers, as well as in churches and women,

only pretensions put forth to prevent examination and conceal frailty or error.-ED.

CHEMISTRY AS A SCIENCE. Art. XIX.

GOLD. PLATINUM.

GOLD is always found native or in its metallic state; sometimes it is alloyed with copper or silver, and occasionally with tellurium. Some species of pyrites also contain a sufficient quantity of gold to make it worth while to extract it. The most usual forms in which metallic gold is found, are grains, leaves, and small crystals. It is contained in the sands of many rivers, both in Africa and Europe, and is found abundantly in South America and India. France, Sweden, Norway, and Ireland all possess gold. Spain was formerly celebrated for its mines, but the principal places where this metal is now procured are South America, Hungary, and Germany. Though not so abundant as iron, nor so easily procured, it is, perhaps, as widely scattered through the mineral kingdom, and has been certainly as long, if not longer known. At present it is not put to so many uses as iron, nor is it so indispensible for the welfare of man. An experience of twenty years, during which it was rarely seen in England, has shown, too, that its place as money, for which it was considered as the best adapted of all the metals, may be advantageously supplied by a material that does not cost so much to obtain it, and is kept in repair at a much less expense. Theory also has stepped in, and confirmed the observations of experience. According to that, it is only necessary that those who promise to pay on demand, should be under an obligation to fulfil their engagements, or at least should not be exonerated from fulfilling them, to make their "promises to pay," or bank-notes, a better and more convenient money than gold. In fact, gold, as money, has no other utility than representing other commodities;

but it is of itself a very costly thing, while its representative faculty may be equally as well performed by paper, which costs little or nothing. By using paper, which would never have been brought into discredit but for the unjust manner in which those who promised to pay were exonerated from fulfilling their engagements, mankind would save all the expense, which is very considerable, of a metallic currency. Thus, therefore, in alluding to the uses of gold, we cannot say much in its favour as money. The expense of procuring it, however, its great durability, its remaining unaltered when exposed to the action of the atmosphere and to great heats, make it,-after bank-notes, to represent certain quantities of it as that commodity which is least liable to alteration, the best material we possess for coin. This is, indeed, a most valuable use, and it is as money that gold is most extensively employed. It is, moreover, of considerable use in the arts: though we never can place a gold drinkingcup on a level with a good knife, in point of utility, yet, if the latter is a useful instrument, the former is a graceful ornament, and the severe morality which would lead us to despise trinkets and ornaments, is as unworthy of the approbation of a wise man, as that fashionable sort of humbug which scorns as vulgar every thing useful. One of the most valuable properties of gold, however, seems to be of modern discovery: it forms, in various ways, some of the most brilliant colours and dyes the moderns possess. Without iron the progress of man would be very slow and circumscribed, and with out gold life would be less adorned and less graceful.

1

When gold is found in the sand of rivers, no other process is employed than to wash the sand well with a quantity of water, so that all the lighter particles are carried off. In general, the quantity of metal contained in the sand is so small that this process, though there seems nothing costly in it, requires

so much time and labour, as, in fact, to be very expensive. Gold has, indeed, been found so plentiful, that the Spaniards, on one occasion, collected in a few hours upwards of thirty thousand pounds worth. One piece weighed 132 ounces, and was worth 5001.; but such mines are like hidden treasures; and if they were frequent," and could be worked at pleasure, would reduce the value of the metal below that of copper. When gold is found alloyed with silver, and mixed with earthy matter, the ore is first broken into pieces about the size of a nut, separated as much as possible from earthy matter, and afterwards reduced to a fine powder. By the addition of salt and water, this is made into a thin paste, mercury is then squeezed into it through a leather bag, and is intimately mixed with it. The mixture is kept at the temperature of boiling water about three days, when the earthy matter is separated by washing, and an amalgam remains of gold and silver. The mercury is distilled off, and the silver separated by cupellation and parting, or subjecting the metals to the action of nitric acid, which dissolves the silver and leaves the? gold. When other metals besides silver are mixed with the ore, it is pounded, washed, and the gold after wards separated by cupellation." When the proportion of gold to silver is much less than 1-4th, it is separated by heating the alloy with 1-8th part of sulphur, and when it has been fused for about H three hours, it is poured into cones greased on the inside. As it cools, the gold sinks to the bottom, and a sulphuret of silver remains at the top. There are other processes for procuring gold, but being neither generally practised, nor of an in teresting nature, we shall say nothing about them.

The chemical and mechanical properties of gold may be described in a few words:-Its colour is reddish-yellow, and in lustre it does→ not equal mercury, silver, steel, or platinum, though it is superior to all other metals. It is rather softer