buoyancy, and, consequently, be seen, by an observer, at a much greater distance than those in ordinary use, and also be kept much steadier, particularly in a rough sea, or tide, way.

The patentee claims the construction, or formation, of buoys, or water marks, having the lower end open for the admission of water for a certain space, and apertures at the upper part of the open compartment, to allow the air to escape, as herein particularly set forth and described, and also shown in the drawing, whether such buoys, or water marks, be made of iron, wood, or other materials.-Enrolled in the Petty Bag Office, September, 1843.

Lond. Journ. Arts & Scien.

Mechanics, Physics, and Chemistry.

On a re-arrangement of the Molecules of a Body after Solidification. By ROBERT WARINGTON, ESQ.

Having occasion lately to prepare some alloys of lead for the purpose of lecture illustration, I was much surprised at an alteration taking place in the arrangement of the particles of one of these alloys, as shown by the appearance of the surfaces of fracture, after the metal had assumed the solid form. The alloy experimented on was that known as Newton's fusible metal, composed of 8 parts of bismuth, 5 of lead, and 3 of tin. On pouring this alloy, in the melted state, on a marble slab, and breaking it as soon as solid, and when it may be readily handled, the exposed surfaces were found to exhibit a bright, smooth, or conchoidal metallic appearance, of a tin-white lustre ; and the act of disjunction, at one part, will frequently cause the whole to fly into a number of fragments, analogous to the breaking a piece of unannealed glass.

The metal after this becomes so hot as to burn the fingers if taken up, and when this evolution of heat has ceased, the alloy will be found to have entirely altered its characters, having lost its extreme brittleness, requiring to be bent to and fro several times before it will break, and presenting, on fracture, a fine granular, or crystalline, surface, of a dark color, and dull, earthy aspect. Similar phenomena accompany the casting of the fusible alloy of H. Rose, composed of 2 parts of bismuth, 1 of lead, and 1 of tin.

The fact of the evolution of heat from the alloy of Newton, and its cause, are thus noticed by Berzelius, in his Traité de Chimie. "If this alloy is plunged into cold water, and quickly withdrawn, and taken in the hand, it becomes sufficiently hot, after a few moments, to burn the fingers. The cause of this phenomenon is, that during the solidification and crystalization of the internal parts, the latent heat of these is set free, and communicates itself to the surface before the fixing and cooling." The alteration in the internal arrangement of the particles, as proved by the surfaces of fracture, is not, however, noticed, and the explanation is defective, as it supposes the interior not to have assumed the solid state, until the evolution of the heat

occurs.

If such were the case it would be seen on breaking it in the first instance. The phenomena can only be accounted for by admitting a certain degree of mobility among the particles, and that a second molecular arrangement takes place after the metal has solidified; this may arise from their not having assumed, in the first state, that direction in which their cohesion was the strongest.

That a very marked and extraordinary alteration in the characters and properties of various substances, arises entirely from this change in the position of their component particles, effected either by the communication, or abstraction, of heat after solidification, there can be no doubt. And these changes are applied to many very important purposes in the arts and manufactures; such as the hardening and tempering of steel, the rolling of commercial zinc, and rendering that metal permanently malleable, the annealing of glass, and a variety of other uses, particularly in crystalization, which might be adduced.

The following experiments were made to ascertain to what extent the emission of latent heat takes place. The melted alloy was poured in a perfectly fluid state on the bulb of a thermometer placed in a small platinum crucible, having a capacity equal to about 70 grain measures of water, and standing in a vessel of cold water, or mercury. The thermometer, surrounded by the solidified metal and crucible, was removed from the cooling medium before it had reached its stationary point, and the greatest decrease of temperature noted. The heat then rose rapidly again, and the maximum effect was registered. The fusing point of the alloy was 202° Fahr.; the following results were obtained:--

So that in four, out of the eight, trials a difference of 60° Fahr. was

rendered apparent.

In a platinum crucible of larger size, the effects were not so marked, 34° Fahr. being the greatest difference obtained; this, of course, would arise from the greater bulk of the melted metal not exposing comparatively so large a surface to the cooling medium.

Mem. Chem. Soc., Lond.

On the conversion of Benzoic Acid into Hippuric Acid, in the Animal Economy. By Mr. ALFRED BARING GARROD, of University College.

A paper has appeared in the Medico-Chirurgical Transactions for last year, and also in the first number of the Pharmaceutical Trans

actions, by Dr. Alexander Ure, in which it is stated, that by the internal administration of benzoic acid, or any of its salts, hippuric acid is formed in the system, and is eliminated from the kidneys in the form of a soluble hippurate, and that this hippurate is formed by the benzoic acid uniting with uric acid. It is also stated, that no trace of uric acid, or any of its salts, could be found in the urine after the administration of the benzoic acid.

I have repeatedly performed Dr. Alex. Ure's experiment, swallowing from a scruple to half a drachm of benzoic acid at a time, and have always obtained a copious crop of crystals of hippuric acid, amounting to from fifteen to twenty-nine grains, by the addition of hydrochloric acid to the urine, passed about three, or four, hours afterwards, (evaporated, or not, according to its state of dilution.) These crystals possessed all the characters of hippuric acid, with the crystaline form, the small solubility in cold water and ether, the ready solubility in alcohol, the evolution of nitrogen, and also the odor of the tonquin bean when heated to destruction; and my experiments, therefore, so far confirm Dr. A. Ure's fundamental observation. He also mentions another test of hippuric acid, viz., that when evaporated to dryness with dilute nitric acid, and ammonia added, a beautiful purple color is produced. This is certainly true of the crystals obtained from the urine, but it is not a character of pure hippuric acid. The cause of this color will be shown presently.

Dr. A. Ure states that no trace of uric acid could be found in the urine; but on examination I have always been able to obtain a distinct trace of uric acid from a drop or two of the urine, by adding a little nitric acid, carefully evaporating, and holding the capsule containing it over ammonia, when a distinct trace of murexide was formed; also, when the dish containing the crystals of hippuric acid is carefully examined, minute grains are found at the bottom, which are uric acid crystals; and on examining the crystals of hippuric acid with the microscope, uric acid crystals are found adhering to them in immense numbers, and this is the cause of the production of the purple color spoken of, and which has been given as a test of hippuric acid. When the crystals are dissolved in alcohol the uric acid is precipitated, and the hippuric acid crystalized from the alcoholic solution no longer gives the purple color. On collecting the uric acid from the same quantity of urine, formed on successive days, the same food being taken, one containing about twenty-seven grains of hippuric acid, and the other none, the following results were obtained:

From 41⁄2 oz. of urine, when no benzoic acid had been taken, uric acid 1.07 grain.

From 41⁄2 oz. of urine, after taking 30 grains of benzoic acid, uric acid 0.96 grain.

Difference in favor of first 0.11 grain.

In the second experiment also, a small loss might have occurred from the greater washing of the crystals necessary in that experiment. Now if we suppose that uric acid is decomposed to afford the elements necessary to be added to benzoic acid to form hippuric acid, we find that each equivalent of benzoic acid requires the addition of

4

6 4

CH. O, N. To obtain the nitrogen, four atoms of benzoic acid would require one atom of uric acid, or half a drachm of benzoic acid would require rather more than ten grains of uric acid. Now the quantity of urine, in the experiment without the benzoic acid, only contained 1.07 grain of uric acid, and yet that quantity was not materially diminished when twenty-eight grains of hippuric acid were found in the urine. It cannot, therefore, be from the uric acid that the hippuric acid is formed.

If we examine the subject theoretically, it does not seem probable that such a body as benzoic acid, possessing such feeble affinities, and producing no sensible action on the body when taken, should be able to break up such a stable compound as uric acid; to abstract from the latter the requisite elements for its conversion into hippuric acid; but as hippuric acid is really formed in the urine, from whence does it obtain the necessary addition? The quantity of urea was noticed in several experiments to be deficient; could this be the source? We can find no rational formula for the explanation of the conversion, if we suppose it to be from urea alone. We can, it is true, select the elements required; but, as in the last case, we should leave some compound in the system, which cannot be resolved into any known compounds, as ammonia, water, carbonic acid, &c., while from the ready conversion of the benzoic acid into hippuric acid we should expect that the change was one which could easily take place, without the action of any unusual affinities being brought into play. It occurred to me that it might be the lactate of urea, instead of pure urea, which is taken up; and upon comparing the formula for hippuric acid, benzoic acid, and the lactate of urea, it appeared that one equivalent of lactate of urea minus three eqs. of water, gave exactly the requisite elements for the conversion of 2 eqs. of benzoic acid into 2 eqs. of hippuric acid. 2 eqs. of benzoic acid +1 eq. of lactate of urea➡2 eqs. of hippuric acid +3 eqs. of water.

Now the urea has, by MM. Cap and Henry, been found to exist in human urine as lactate, and the separation of the elements of water is a change which might be expected to take place in the system under such circumstances. The benzoic acid merely taking up the lactate of urea, and throwing off water, is certainly a more probable occurrence, than the destruction of such a stable compound as uric acid.

In analyses for the quantity of lactate of urea, according to the method of Cap and Henry, I found that although I could not obtain it in crystals, yet the quantity in a siropy state was much reduced

after taking the benzoic acid, and the same appeared on forming nitrate of urea from it. I obtained 14 grains less of urea in 41⁄2 ozs. of urine when the benzoic acid had been taken. In another experiment I obtained 17 grs. less of urea when 30 grs. of benzoic acid had been taken; this is a greater loss than can be accounted for by the formation of the hippuric acid; but this can be referred to the urine, from some accidental circumstance, being of nearly as high specific gravity, in this case, as when the benzoic acid had been taken. 30 grs. of benzoic acid, swallowed, usually increased the specific gravity of the urine from four to six-thousandths.

From these results two inquiries suggest themselves:-1st, may not hippuric acid be formed artificially out of the body? 2nd, if sufficient benzoic acid were swallowed at such a time when the least urea was contained in the urine, would the benzoic acid not cease to be all converted into hippuric acid, part of it then appearing in the urine unchanged?

Ibid.

Iron Founding.-From the Glasgow Practical Mechanic and Engineer's Magazine.

(Continued from page 196.)

SECTION IV.-LOAM-MOULDING.

Loam-moulding, the last branch of the art, as it has been treated in these papers, falls to be discussed in the present article. As already described, the peculiar functions of the loam-moulder is to construct loam patterns and mouldings of certain cast-iron work, by which the mould may be formed without incurring the expense of the construction of a wood pattern for that purpose. In many cases, also, the loam-moulder constructs moulds for which wood patterns could not be provided. The economical employment, however, of loam as a substitute for wood patterns and sand, is restricted, in general, to the manufacture of the more regularly shaped work of a foundry. Every variety of circular bodies may be done in loam: large square vessels, too, are done by the same process.

Every piece of loam-moulding, of any considerable extent, is a regularly built structure, being composed of bricks, arranged in layers, and bedded in loam, in which they are also entirely enveloped, particularly on those sides contiguous to the mould. The composition of loam demands strict attention, varied, as it requires to be, suitably to the various applications of loam. Two indispensable qualities are those of firmness and porosity. The first is evidently necessary, considering the very great hydrostatic pressure to which, in large castings, mouldings are subjected, while the iron is liquid. And again, the copious effusion of gases from the mould, arising from the action of the heat of the cast, renders it absolutely necessary to provide for their escape through the material of the mould. This is provided for in the porosity of the mass, which must, therefore, be in such a degree as to offer a transit sufficiently free to the airs evolved, while the mould