of war; and there seems every reason to expect (unless causes should interfere, of which our present knowledge gives no indications,) that small quantities of zinc, or, which is much cheaper, of malleable or cast iron, placed in contact with the copper sheeting of ships, which is all in electrical connexion, will entirely prevent its corrosion. And as negative electricity cannot be supposed favourable to animal or vegetable life, and as it occasions the deposition of magnesia, a substance exceedingly noxious to land vegetables, upon the copper surface, and as it must assist in preserving its polish, there is considerable ground for hoping that the same application will keep the bottoms of ships clean, a circumstance of great importance both in trade and naval war.

It will be unnecessary for me to dwell upon the economical results of this discovery, should it be successful in actual practice, or to point out its uses in this great maritime and commercial country.

I might describe other applications of the principles to the preservation of iron, steel, tin, brass, and various useful metals; but I shall reserve this part of the subject for another communication to the Royal Society. From the Philosophical Transactions for 1824. Part I, just published.

BORAX.

We understand, by a communication from a Correspondent, that we were mistaken in supposing that this salt is not yet manufactured in England. He assures us, that there are three or four manufactories of borax in London, and that the acid is imported in large quantities. The mode in which we expressed ourselves must, however, satisfy him, that we were at the time not confident on the subject; and that our mistake was a very venial one, since chemical works of high authority, published in 1824, 1, mention borax as still imported from India, and say nothing of its being manufactured in Eng

land. We are happy to learn that we are mistaken, and that, in small things as well as great, the zeal and enterprize of our countrymen are equally conspicuous.

TESTS FOR METALS. To the Editor of the Chemist. Aug. 4. SIR, I have often observed, that the three universal tests for metals, viz. tincture of galls, sulphuretted hydrogen, and prussiate of potass, precipitate many of the metals but very imperfectly, and so many of the same colour, that it is often almost impossible to be sure, whether it is one metal or another which is held in solution. Besides this, if one metal resemble another in appearance, and at the same time the precipitates formed by these tests are similar, the difficulty is much augmented. Tin and lead are an instance of this; they both give a white precipitate with prussiate of potass.

Now I have found, that the bydriodate of zinc will precipitate most of the metals, and no two metals resembling each other give the same coloured precipitate with it. Besides, the hydriodate of zinc is prepared in the utmost purity, merely by digesting zinc, iodine, and distilled water together, while it is very difficult to obtain the prussiate of potass perfectly pure; and, if not pure, it is liable to give false results.

I should remark, however, that the different acids with which the metals are combined make a material difference in the colours of the precipitates.

Table of Precipitates formed by Metallic Salts with Hydriodate of Zine, Muriate of Gold, no precipitate. Nitrate of Silver, yellowish-white. Muriate of Platinum, deep brownish-red precipitate, which remains suspended.

Nitrate of Mercury, dirty orange.
Muriate of Arsenic, no precipi-

tate.

Muriate of Tin, no precipitate. Nitrate of Lead, bright lemon colour.

you

PROBLEMATICUS.

RANCID BUTTER. To the Editor of the Chemist. SIR,-If think it worth insertion in the Chemist, the following will be found a simple and effectual mode of preventing the rancidity of butter for several months.

Press and beat all the milk out of the butter, then divide it into separate pounds. Put each pound into a linen cloth moistened with common salt and water, deposit them in a stone jar, and fill it up

with the same mixture. Place a slate over the mouth of the jar till the butter is wanted for use. Call me, if you please,

ANOTHER DAIRYMAID

QUERIES.

To the Editor of the Chemist. Croydon, Aug. 2. SIR, I have now before me a Number of the New Monthly Magazine, from which I copy the following:

"Professor Meinecke, of Halle, has just succeeded in producing a brilliant illumination by means of electric light, and with the aid of an artificial air inclosed in glass tubes."

If, Sir, either of your Correspondents can inform me how to do the like, and will be so good as to communicate such information inclosed to you, I shall be thankful; and if it answers I will endea. vour to make satisfactory remune, ration.

I respectfully subscribe myself,
Sir,

Your attentive reader,
ELECTRICICUS.

SIR, I have a friend, a veterinary surgeon, who informs me that he has employed, for the last six months, sulphuret of copper, given in doses of from three drachms to an ounce and a half, daily, for the cure of the disease termed glanders. It is given in solution. One of his patients (a horse or an ass?) in particular, must have taken upwards of fourteen pounds of this substance, and yet, after death, he could not detect the least trace of copper in any of the secretions. It appears to act as a tonic and astringent on the system generally.

The only test that he has employed, is a piece of burnished iron or steel, thinking if there were any copper present, it might be precipitated by the superior affinity of

the acid for the steel.

If you, Mr. Editor, or any of inform me in what manner I can your numerous correspondents, can proceed to detect its presence, either in the blood, urine, or fæces, you will much oblige

A constant reader,
London, Aug. 8.
W. F.

ANSWER TO QUERY. We cannot exactly solve all the difficulties pointed out by Chemicus Ignoramus; but there are two facts, one relative to the muriates, and another in his statement, which will probably enable him to see

his way to a solution. In his third note, which we characterised as more marvellous than the two former, he says, the pasteboard never was wet. But in his second letter, it is mentioned, that not above one or two crystals formed on the under side of the card, whence it is evident, that the card must have been wet; and as the dish was at first nearly full, the card, we suppose, was the means of conveying the solution from one dish to the other. There can be no doubt but the outside of the upper dish would appear more or less wet according to the state of the atmosphere, all the muriates having a very great affinity for moisture; and what our Correspondent states in the first letter, of the outside never having been wet, is contradicted by what he states in the second, and must, we should suppose, have arisen from inaccurate observation. The general fact relative to the muriates, to which we have alluded, is very curious, and we shall transcribe it from Mr. Parkes' Chem. Cat. page 189:"The muriates are among the most volatile, and yet are the least decomposable by fire of all the salts." "Muriate of soda (common salt) may be volatilized by heat, but if the vapour be collected, it will be found still to be muriate of soda."

Our Correspondent must, we should suppose, be quite aware, that it is not possible for the solution to escape from one dish into the other by evaporation. Evaporation would have carried it off into the atmosphere; the solution, therefore, was conveyed from one dish to the other by some mechanical means, and was of course equally salt in

both.-ED.

SULPHURETTED HYDROGEN GAS.

To the Editor of the Chemist. SIR, I agree with my friend' Cat's-paw as to the effects of sulphuretted hydrogen, and the incorrectness of M. Chaussier's statement. I placed a mouse under a receiver full of this gas, and kept

it there for more than three minutes, after which he recovered. Yours, &c.

CHLORINE.

P.S. I hope to send you in a day or two a description of a new alkali, which I have discovered in the senna folia.

TO CORRESPONDENTS.

The letter of W. M. S. is scarcely fit for publication; we thank him, however, for the information he has afforded us, and have made use of it to rectify the error committed."

The other communication of Chlorine in our next. We regret as much as he can do the circumstance of quacks and ignorant people injuring the health of his majesty's subjects by selling them improper drugs; but we cannot agree with him that it is right to call on government to interfere. In this respect, people must help themselves; and the way in which they can easily accomplish this, is by only purchasing of respectable dealers. Individual sharpness and discretion is a better preventive of such evils than the interference of government. We shall be happy to receive the communication he promises us.

We are obliged to Damon for defending us against the imputation of Castigator; but his letter is too long, and, we must say, too severe for publication. If he will reduce it to about the length of Castigator's letter, we will, however, insert it.

Chemistry as a Science. Art. XXIII.

General Characteristics of the
Metals.........

373

ib.

A

374

381

Analysis of Scientific Journals. The
Technical Repository for August.. ib.
Discovery of a Mine of Quicksilver
at Idria, in Carniela..

CHLORATE OF POTASH. SIR-I observed in Number XX. of The Chemist, a tedious method described of making chlorate of potash, which may be more easily obtained by the following method:-Three jars are to be procured, one of which is to be double the size of the others, and the large one is to answer the purpose of a retort. A solution of potash is to be placed in the two small ones, three quarts in the first

383

ib.

jar and one quart in the latter. The retort is to be placed in a sand or water-bath (I prefer the latter,) and one and a half peroxide of manganese, three muriate of soda, and three of water placed in it. The three vessels are all afterwards to be well luted together with a luting of linseed meal; after which is added, very gradually, by the funnel, sulphuric acid. When the chlorine ceases to come over, or begins to come less ra

pidly, heat is applied to the bath, and chlorine will be again extricated. During the process the solution will appear white and milky, owing to the silica in the potash, which will gradually be precipitated, and the chlorate of potash will be deposited at the bottom and sides of the jar. The fluid (which is excellent bleaching liquid) is to be drained off, and boiling water poured upon the remainder, which is a solution of chlorate of potash, the silica remaining. The solution is to be afterwards evaporated and crystallized. Yours, &c.

STEAM-ENGINES.

We have for some time past had the intention of endeavouring to give our readers a concise account of the improvements said to have been made in the steam-engine by Mr. Perkins. Before we have been able to execute our intentions, we find it done to our hand in a very able work, which has just fallen under our notice, and from which we shall make some extracts. Its title is, "A DESCRIPTIVE HISTORY OF THE STEAM-ENGINE, by Robert Stuart, Esq. ;" and the object of the book is to give a history of the invention and improvement of steam-engines.

The author, beginning from the earliest notice he can find, of the employment of steam as a moving power, which he traces up to a period before the birth of Christ, has recorded every valuable improvement or considerable alteration which has been made in steamengines up to the present time. His book is intended, he says,

* One volume 8vo, with forty-seven engravings of different engines,

"particularly for the meritorious classes who are engaged in the construction of machinery;" and being enriched with numerous plates, illustrating the progress of the art of making steam-engines, must be of considerable interest to all who live by the mechanic arts, or study them as a branch of general knowledge. Its great merit, as it appears to us, is having brought into a small compass and a cheap form all which is worth knowing of the history of steam-engines. The author has set in a clear point of view the contested claims of different ingenious men, as to having invented or improved different parts of the engine; and, if such a thing were possible, we might expect that even partisans would now cease to dispute on these difficult matters.

We shall at present content ourselves with making the following extract, which we think our readers will find both amusing and instructive :

“ The introduction of the steamengine into Peru arose from a series of incidents which have almost the air of romance. We have described the high pressure engine of Mr. Richard Trevithick, for which he obtained a patent in 1802. In order to give a better idea of the arrangement and operation of his engine, he had constructed a working model, which was so highly finished that it had found its way to London as a cabinet curiosity.

"About the same. period M. François Uvillé had found in Peru some of the richest mines falling into decay, or totally drowned, from the impossibility of draining them by manual labour; and learning also that these mines were considered to be richer in silver ore than those of Mexico, he conceived the idea of introducing the steamengine as a substitute for animal power, to accomplish their draining. M. Uvillé came to London in 1811; but among those whose opinions he asked, he met with no encouragement to pursue his plan, on account of the inefficacy of steam in an atmosphere so rare as that in