which is generally found in the shops, and is worked with singular facility. Recent sections made with a sharp knife or scissors, when brought together and pressed, adhere so firmly as to resist rupture as strongly as any other part, so that if two sheets be laid together and cut round, the mere act of cutting joins the edges, and a little' pressure on them makes a perfect bag of one piece of substance. The adhesion of the substance in those parts where it is not required, is entirely prevented by rubbing them with a little flour or other substance in fine powder. In this way flexible tube catheters, &c. are prepared; the tubes being intended for experiments on gases, and where occasion might require they should sustain considerable internal pressure, are made double, and have a piece of twine twisted spirally round between the two. This, therefore, is imbedded in the caoutchouc, and at the same time that it allows of any extension in length of the tube, prevents its expanding laterally.

The caoutchouc is, in this state, exceedingly, elastic. Bags made of it, as before described, have been expanded by having air forced into them until the caoutchouc was quite transparent; and when expanded by hydrogen they were so light as to form balloons with conconsiderable ascending power, but the hydrogen gradually escaped, perhaps through the pores of this thin film of caoutchouc. On expanding the bags in this way the junctions yielded like the other parts, and ultimately disappeared.

When cut thin, or when extended, this substance forms excellent washers, or collars for stop-cocks, very little pressure being sufficient to render them perfectly tight. Leather has also been coated on one surface with the caoutchouc, and without being at all adhesive, or having any particular odour, is perfectly water-tight.

Before caoutchouc was thus worked, it was often observed how many uses it might in such a case

be applied to; now that it is so worked, it is surprising how few the cases are in which persons are induced to use it. Even for bougies and catheters it does not come into usc, although one would suppose that the material was eminently fitted for the construction of these instruments.- Quarterly Journal.

ON

PROCURING OXYGEN

FROM MANGANESE. To the Editor of the Chemist. SIR,-The oxide of manganese of commerce, or otherwise the peroxide of manganese, is very seldom found free from carbon. There are two tests to discover this; first, which is, however, not the most certain, generally the peroxide of manganese, which is crystallized in shining needles, is not carbonated; secondly, reduce the peroxide to powder, and pour on it some nitric acid: if it is carbonated, an effervescence will take place immediately. If the chemist, therefore, wishes to employ such an oxide, he should previously agitate it in an earthen vessel with an excess of dilute muriatic acid. The carbonic acid gas is set at liberty; and as soon as the effervescence is finished, the chemist has only to pour out the liquid, to wash the oxide once or twice with a great deal of water, and then to dry it; it is afterwards fit for use, and will produce very pure oxygen. Without this previous step, on the bottle being heated to a high temperature, the carbonic acid gas would be disengaged during the operation, and would render the result Very different from what was expected.

Such, Sir, is the process recommended in this case by several chemists, particularly by Lavoisier and Thenard.

I am, Sir,
Your obedient servant,
A* D*

July 10.

QUERIES.

To the Editor of the Chemist. SIR,--Having succeeded more than once in obtaining abundance of hydrogen gas, I made a balloon of fine tissue paper, which I could fill tolerably well with the common bellows; but when I made an attempt to fill it with hydrogen, my hopes were all frustrated, it would not fill at all. I tried again, but with the same result. I can only account for this, by concluding, that the gas being more subtle than common air, penetrated through the pores of the paper. Now, Sir, I should be obliged to you, or some of your Correspondents, to inform me of the cheapest way in which I could make and fill a balloon on a small scale, to send up without any burden, and whether or not one could be made of paper?

A YOUNG ADMIRER OF CHEMISTRY. July 9.

Is it possible to find a cement or putty, which could not be attacked by sulphuric acid?

ANSWERS TO QUERIES. MR. EDITOR, Having seen several Queries in No. XVII. of The Chemist, I shall proceed to answer some of them to the best of my knowledge.

First, The best method of obtaining sulphur from native sulphuret of iron, upon a large scale, so that sulphuric acid may be obtained from the disengaged sulphur, is by sublimation in large glass or earthenware matrasses or subliming pots, which are placed in large round sand-baths; but sulphate of iron cannot be obtained from the residue, if it be entirely or nearly void of sulphur, for the sulphur is necessary to the formation of the sulphuric acid of the sulphate of iron. But if much sulphur be left in the residue, or if the sulphuret of iron in its natural state be used for making sulphate of iron, the operation must be carried on in the following manner :The sulphuret of iron being broken up, it is to be exposed in one large

heap to the air and rain for at least twelve months. The heap should: have a channel all round it, with another leading to a large reservoir, in which the solution of sulphate of iron is to be received, and from thence it is to be conveyed to: the boilers for boiling it down to. crystallize. In this process the sulphur is acidified, and the iron, oxidated by the oxygen of the air and water. Part of the water dis-: solves the sulphate of iron as it is. formed, and carries it into the reservoir.

Your same correspondentwishes to know, if heat and light are really emitted, or only reflected by the sun? This question, I fear, he will not get satisfactorily answered, as there are several theories about it, none of which can be satisfactorily proved. Some have said that the sun merely reflects the heat and light of the earth; others, that it is the primary source of both. Some have even gone so far as to assert that it is a solid mass of phospho

rus!

In short, it is quite above our comprehension.

Solar light is not different in its nature from the light emitted during combustion, animal decomposition, percussion, or friction.

Should this meet your approbation, I shall feel myself obliged by, its insertion, and remain,

Your humble servant,
PROBLEMATICUS.

TO STAIN THE HAIR, MR. EDITOR,-In reply to your correspondent Prism, I beg to state, that a solution of muriate of gold diluted with water, stains the air of a brown or auburn colour, and this colour is as permanent as the hair. July 6.

SIMPLE TESTS FOR OXALIC ACID.

(From a Correspondent.)

LET a few drops of vinegar be mixed with the solution; if it is oxalic acid its colour will change, if Epsom salts it will not. As it respects the taste, if the tip of the

tongue be applied to the solution the detection will instantly appear, and without danger, for oxalic acid is strong, hot, and very sour; Epsom salts have merely a gentle sort of bitter saltness. Or, dip the end of a piece of dark purple paper (procure it from the grocer's) into the solution; if oxalic acid, the colour of the paper will change to a bright red; on the other hand, if Epsom salts, it remains unchanged. Or, dip a silver spoon, or put a sixpence into the solution; if oxalic acid the colour of the silver will be changed: or if some of the supposed solution be poured on a heated plate of iron, (the fire-shovel will do) if oxalic acid it will, when evaporated, leave a brown sediment; but if Epsom salts, it will leave a white powder.

BUGS DESTROYED BY
STEAM.

MR. SEALY, of New York, has announced, that steam is an effectual means of destroying this noxious insect. It is only requisite to expose the place where they herd for a short time to the action of steam, and the more the water boils the better; it kills the eggs as well as the vermin. The employment of this method is both so convenient and cleanly that we think we need say nothing of the mode of applying it, nor by way of recommending it to trial.

* POISONOUS CATSUP.

FISH eaters and catsup buyers, look sharp, for you may be taken in and poisoned! Catsup is, in fact, adulterated in a most reprehensible way. Much of what is sold abounds with copper, which is highly deleterious. After the process for obtaining distilled vinegar has been completed, the residuum is diluted with a decoction of the outer green husk of walnuts; it is then spiced with Cayenne pepper, pimento, garlic, common salt, and allspice, and sold for walnut catsup. The quantity of poison in this substance is greater than is met with in any other article of food or

sauce.

ce. Although it is taken in

such small quantities as not to be at the moment perceptibly mischievous, yet, in the long run, it is very much so, and from its cheapness, this sauce is very generally used. We recommend lovers of fish, therefore, to adopt Mr. Mariner's method of eating them. That gentleman, from his long residence at the Tonga Islands, acquired an invincible partiality for raw unadulterated fish, which he said were in that state preferable to carp stewed in wine, or turbot swimming in lobster sauce. His recommendation, we are told, has made eating raw fish somewhat fashionable, and as ladies now eat fish with their fingers, (see Times, July 2,) there may be some apprehension that we are relapsing into the barbarity of our primeval ancestors, or, what is worse, adopting the customs of the Esquimaux.

TO PREPARE SOLAR PHOSPHORUS.

CLEANSE oyster-shells by well washing, expose them to a red heat for half an hour, separate the purest part, and put it into a crucible (a small old flower-pot answers very well) in alternate layers with sulphur, till almost full; expose the vessel to a red heat for one hour at least; when cold, break the mass, and separate the whitest parts for use. When inclosed in a bottle, the figures of a watch may be distinguished by its light.Me= } chanic's Magazine.

TO PROCURE GOOD WATER

FROM SEA WATER.

CHEMISTRY AS A SCIENCE. Art. XVIII.

SILVER.

THERE is scarcely a country of the world where this metal is not found, and formerly it was procured to a considerable extent in several parts of Europe. The discovery of mines in America, in which it was much more abundant, and could be worked at a much less expense than in the silver mines of Europe, made it cease to be advantageous to work the latter, and many of them were abandoned. Silver is still obtained in various parts of the Continent; and a small quantity even is got from working lead mines in both Ireland and England. America, however, is the

great storehouse of this metal at present; and Humboldt says that the mines in three centuries have. afforded 316,023,883 pounds troy of pure silver, which would form a solid globe, 91.206 feet in diameter. But the richest and most productive of these mines is of comparative modern discovery, which gives some countenance to the opinion, that if America were properly peopled, and processes for abridging labour as numerous there as they are here, that silver would be as cheap as copper, and we should all be obliged to have recourse to paper money, as the only means by which we could carry enough about with us for our ordinary expenses. The following is given by M. Brog

Total from Amer. 2,285,000 lbs. per year.

If we multiply this last sum by 300 years, we shall obtain, as the probable supply for the next 300 years, more than double the quantity of that immense load which, according to Humboldt, has been already extracted from America. Notwithstanding this large supply, it would appear to be used and worn out almost as fast as it is obtained; for there is no great accumulation of silver in any part of the world, and the quantity has only, since the effect of the first discovery of the mines in America has fully taken place, reduced the value of silver a very little, compared with other commodities. In fact, however abundantly a metal may exist, not its quantity, but the trouble or labour necessary to procure it determines its value relative to other commodities. And as the labour and trouble of procuring silver ore, and separating the metal from other substances, will most probably always be considerable, it will require a large share of other commodities to purchase it. The principal process by which it is obtained at present is very costly, though there is some chance that this may be improved. It is called amalgamation, from being effected by mercury; and as

it is a curious process, we shall here give a short account of it.

There are numerous silver ores, but the principal ones are the native silver pre and a mixture of sulphuretted silver and lead. The native silver ore is the ore chiefly subjected to the amalgamating process, and it is employed as the cheapest method for ores that are not very rich. The inventor of this method, it is said, was a miner of Pachuca, called Bartholomew de Medina, and it dates from the year 1557; but some authors say that the Germans were acquainted with it, and practised it, long before that period. In Mexico the metal is first reduced to powder, and, according to M. Humboldt, this operation is there conducted with very great care. After being pulverized, it is sifted through a piece of leather pierced with holes, and again ground by stones moving in troughs. Each mill of this species, called in America arastras, grinds from eight to ten hundred weight of mineral in twenty-four hours. If the mine is rich, so much care is not employed in reducing the mineral to powder; it is sufficient if it be bruised of the size of coarse sand. When the schlich, as it is called, is thought to be fine enough, it is carried, while yet wet, into the amalgamating yard, which in general is paved with large stones. It is there heaped up in masses of from 20 to 30 cwt., and 40 or 50 of these heaps make what is called a tourte. This quantity is then left to itself for a considerable time, after which common salt is added, in the proportion of from 4 to 20 per cent., as the ore is poor or rich; if the ore does not contain, as it sometimes does, pyrites or sulphate of iron, this substance is also added, mixed with sulphate of copper, and finally, lime and vege table ashes are put on the heap. These different substances are carefully mixed, and allowed to remain together for several days. According to the nature of the ore, their action on one another is different. If it is naturally loaded with the sulphates of copper and