ers contained very little water, and had suddenly thrown in a plentiful supply.

Doubts as to the development of steam by heated metal have led to the supposition that water is decomposed in an unduly heated boiler, giving rise to the production of hydrogen gas.* We have always considered the attempts to explain explosions in this way as entire failures, from the impossibility of furnishing free oxygen to the hydrogen within the boiler to produce an explosion. The Committee whose labours are under discussion have made an elaborate set of experiments, to ascertain if water is decomposed, as has been assumed, when thrown into a red hot boiler. They find that no such decomposition takes place, and thus remove the very foundation of the hypothesis. They admit that carburetted hydrogen does, no doubt, exist at times in a boiler, in greater or less quantities, from the decomposition of oil or of vegetable substances introduced to stop leaks or to prevent deposits; but consider that there is no warrant for the idea that this gas can accumulate and mix with air within a boiler, so as to become a source of danger.

They then consider some cases of explosions which have been assumed as produced by hydrogen, particularly one which occurred at Pittsburgh in the United States. A cylindrical boiler was thrown up into the air, and a stream of fire described as issuing from it, by an eye witness of the explosion. This observation they explain by the optical phenomenon always occurring when luminous bodies are viewed in rapid motion.

Having proved that danger results from heated metal within a boiler, and disposed of various hypotheses connected with this fact of the subject, the Committee proceed to examine the probable causes which may lead to this source of danger, and the remedies which have been suggested to meet them.

The causes examined are: first, a deficient supply of water within a boiler; second, the existence of deposits from the water used to supply the boiler, or from other sources; third, in the particular arrangement of contiguous and communicating boilers on board of steam boats, by the deck of the boat being inclined to the horizon.

In all these cases it is necessary to shew, not merely that heated metal will result, but that water can get access to it; otherwise no dangerous effects follow. In the first case, besides the ordinary circumstances which suggest themselves, such as the introduction of water by a hand pump, the removal of an obstacle from the forcing pump which supplies the boiler with water, &c., a less obvious train of circumstances has been assumed as operative. When water is suddenly relieved from pressure, this hypothesis asserts that it foams up, and

This, with other errors which these Reports would have explained, if circulated in a popular form, appears in the evidence before the coroner's inquest in the matter of the late explosion at Hull.

that the foam being thrown upon the hot iron, is instantly vaporized. If this be true there are cases in which the opening of a safety valve may be a source of danger instead of one of safety! And this result was actually found experimentally to be true by M. M. Tabareau and Rey, of Lyons. But the fact of this foaming is also interesting as affecting the indications of the gauge-cocks and floats, commonly used to show the level of the water in a boiler. It must be especially effective in a small high pressure boiler.

The Committee found, by experiment, that when water boiling under pressure is relieved from that pressure a foaming commences, near the point at which the relief is given, extending throughout the fluid. That this is greater as the opening made is greater, the relief more sudden, and the previous pressure greater. In one of the experiments indications of water were found by a guage-cock two inches above the true level of the water in the small experimental boiler, these guage-cocks being at the time open.

The glass guage-tube used in our locomotive engines they found not to be affected by this foaming, until it reached the top of the tube. They recommend its use strongly, and propose to substitute green glass in high pressure boilers, for the white glass which erodes under the action of high steam.

It is obviously impossible to determine, as a general phenomenon, whether the steam produced by the projection of foam upon the heated sides of the boiler, produces more steam than that which escapes through the opening causing the foaming. It depends upon circumstances liable to vary in every case. This view the Committee take of the subject. They refer to the experiments of M. Arago, at Paris, made upon boilers not unduly heated, in which the mercury guage always fell on making an opening from the boiler; to their own experiments on a boiler of which the sides were heated when the same result followed; and to those of M. M. Tabareau and Rey, when the boiler was surrounded by a charcoal fire, and when the reverse always took place, the pressure being increased by making an opening. It must be admitted then, that with a boiler presenting a great extent of highly heated surface upon which foam may be thrown, the making of an opening may be attended with danger. Indeed the successive explosions, recorded by Mr. John Taylor to have occurred in connected boilers in the Polgooth mines, do not admit a contrary supposition, for the second boiler had just had an opening of large size made by the explosion of the first, with which it had been in connection.

To avoid the source of danger resulting from the presence of heated metal, it is necessary to have some means of ascertaining the temperature of those parts of a boiler which are most liable to become overheated, so as to give notice before they reach a temperature at which danger would result. The Committee discuss various inventions which have been brought before them for this purpose, and give the experiments made upon one proposed by their chairman.

These experiments, which were favourable, were made the upon apparatus shown in the annexed figure. A B is a section through the top

of a boiler; C D is the flue, or fire-place, to which the tube RL is supposed to be fastened at the bottom, the flue closing the tube. The lower part, HI, of the tube contains a small quantity of fusible metal, by which a stem, L K, is soldered, as it were, to the flue. The weight, M, upon the lever, P K, tends to draw the stem, K L, upwards, and, when the fusible metal is softened, will actually disengage the stem. The weight, M, descending,

rings the bell, N, giving notice that the proper limit of temperature has been reached. If by throwing cold water into the boiler, which at this temperature may be done without danger, or by other appropriate means, the temperature of the flue is reduced, the stem, K L, having previously put in its place, is soldered again to the flue, and the weight, M, being applied to the lever at P, the apparatus is ready for action.*

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The second cause assigned for the undue heating of parts of a boiler is the accumulation of sedimentary matter upon them. this the boilers of steam boats plying on the western rivers of the United States are stated to be particularly exposed, those waters containing both mud and calcareous matter in great abundance. The facts brought together, from different quarters, in relation to sediments from salt water, from river water, and spring water, are interesting. They are examined with a view to the application of various remedies which have been proposed to the Committee, none of which, however, are considered as proper substitutes for frequent

On this apparatus, the Magazine of Popular Science has these remarks: "No doubt! there can be no doubt of this effect occurring, the most perfect fluidity may be obtained; but cui bono ?-for what purpose ?" We can scarcely understand how an individual should be so dull, the mode of action seems level to so mean a capacity. Perhaps our cotemporary was not aware that letting off steam was not always the "true remedy" to the danger of an overheated boiler. Perhaps he did not see that the same power which rings a bell, will equally open a valve or turn a stop-cock, if required, and that if a large opening is not preferred to be made it is not without cause. Here is his note on the subject; it may be taken as a specimen of his fairness and of his style: "We cannot help thinking that the following parallel case of a "true remedy" would be prescribed by the Sub-committee, if the question were presented to them. Suppose a man has a box which can only be opened by a certain crooked sixpence; what is the best way of being sure to up in have the sixpence always at hand when wanted? Answer.-Shut it the box! enclose the metal in a case!"

cleansing of the boiler. This is impracticable in the connected boilers before referred to, when used on board of steamers; and the fact may serve to explain the frequent explosions which occur in the United States, on the Mississippi river. It is to this kind of boiler that the third mode assigned by which unduly heated metal may be produced is applicable. This form is condemned by the Committee, and is not in use, we believe, for our steamers. We wish they may be successful in preventing the further extension of its use in their own country. When the deck of the steam vessel is inclined by passengers moving to one side, by wind, &c., the upper boilers are more or less emptied of water; they are thus exposed to the fire, without the protection of a covering of water, and become unduly heated. The water which is forced into them on the return of the boat to its proper position is thrown upon the heated metal and flashed into steam.

For a connected view of the conclusions drawn from the discussion of this part of the subject we would refer to the Report itself. One of the articles in which these are exhibited contains a table of alloys applicable to boilers working at pressures from one to thirteen atmospheres, and is deduced from experiments by the Committee, in which much labour must have been encountered, and in the course of which some curious properties of alloys appear to have been developed. The temperatures given in this table as corresponding to the assumed pressures are from data drawn up by the Committee from their own experiments. This differs considerably from that lately given by a Committee of the French Institute. The results, however, are the mean of many experiments, in which the data appear to have been calculated with care. The pressures increase more rapidly with the temperatures than in the table of the French commissioners, agreeing more nearly with the experimental results of Dr. Ure and Professor Robison than with those of other experimenters.

3rd. Explosion may arise from defects in the construction of the boiler or of its appendages.

Under this head are discussed the influence of the form, material, and manufacture of a boiler. The waggon boiler is considered as applicable only when low steam is used. Boilers with interior flues commonly give way by blowing off the heads of the boiler, or by the flattening of the flues. Those in which the flues pass through both heads of the boiler are, cæteris paribus, the most safe, while those in which the flue passes through the steam chamber and top of the boiler are liable to accident. Weakness arising from irregular forms, from the cutting out of the metal by rivets, from the wearing of the junctures of the plates when exposed to the fire, &c., are discussed. Frequent proving of the boiler is recommended, while in use, as the only means of being certain of its retaining the strength shewn in the preliminary proofs before its use.

The Committee consider it important that several valves should be placed in the induction and eduction pipes of the forcing pump which supplies the boiler with water, in order to prevent the derangement

of the pump by sedimentary matter. To ascertain its action at any time, they recommend a small stop-cock in the supply pipe, similar to that used in locomotive boilers.

4th. The carelessness or ignorance of those entrusted with the management of the steam engine may produce, and have produced, the most disastrous accidents. To guard against these the Committee have proposed certain provisions in their project of a law for regulating steam navigation and the steam engine, and to which we must refer for details.

5th. Cases of collapse from a partial vacuum within a boiler or its flues.

The ordinary air-valve is commonly provided, to prevent danger from this source by the condensation of the steam. A singular case, described, by Mr. John Taylor, as having occurred at the Mold Mines, is discussed by the Committee. It appears than an explosive mixture of coal-gas and air was formed in the flues on the closing of a damper, and became ignited. A burst of flame was seen from the mouth of the flue at the moment of explosion. The boiler was one of those with interior flues. The precaution which suggests itself to prevent the possibility of such an accident is an obvious one.

6th. Having closed the subject of the means of preventing explosions, the Committee consider briefly whether it is possible to provide protection against them when they occur.

The means proposed are by carrying passengers in a boat separate from the engine, or by placing the boilers on the "guards" of the boat, and separating them by a suitable bulwark. The first of these plans, it is stated, has been tried in America, and abandoned on account of the impediment to speed. The second, the Committee are of opinion, might be rendered effectual, but they prefer strongly attempts to render the boiler safe to those intended to ward off the effects of its explosion. These means, as far as have occurred to them, are embodied in the project of a law, from the adoption of which we should anticipate much good would result, and which, with the Reports, we recommend to the perusal of our readers.

An Address delivered at the Opening of the Worcestershire Museum, by Charles Hastings, M.D., F.G.S.; to which is subjoined the First Fasiculus of the Statistical and General History of Worcestershire-Parish of Great Witley-by the Rev. Thomas Pearson, Rector of Great Witley, and the Rev. John Pearson. pp. 97, 800. London: Sherwood-Worcester: Deighton.

FOREMOST among the Natural History societies that, like brilliant syngenesious flowers opening before the unclouded sun, met the bright beams of the sun of science, shone forth the Natural History Society of Worcestershire. Its founders seemed men endued with enthusiastic ardour, its patrons appeared liberal and judi