Imágenes de páginas
PDF
EPUB

the precipice at Queenston, and there commence anew its great work of retrocession. It will be seen by reference to fig. 4, that the ravine at Queenston and onward, to the whirlpool, is not parallel to the lateral valley, (represented by dotted lines,) but makes an angle, the apex of which is the head of the valley. When the falls advance to the dotted lines, W, which mark the boundary of this valley of drift, and had broken and cut its way through the hard limestones, &c., into this soft and very thick bed, a violent and rapid excavation would go on by the mighty force exerted from the falling cataract on the soft material, most of which would be carried away in the form of mud. As this drift descended far into the soft shale below the quarztose rock, it is highly probable that it was cleared out, forming a vast circular pit, and it is this which caused the gyratory motion of the water. Fig. 2, W, gives a representation of this pit. Had the falls retrograded a few yards east of the point, W, which represents the head of the valley, there would not have been what is now called the whirlpool; for then it would not have entered the soft bed of drift at the head of the valley, out of which I believe the whirlpool was formed.

On the falls retreating from the whirlpool, it will be noticed, that the hard quartzose rock, 2, fig. 2, would form the base of the falls, and then an obstruction would be made to the free egress of the water; the hard rocks would then fall on this pavement, which would greatly increase the obstruction and give rise to the rapids, and this would continue as the falls receded, until by the indication of the strata, this hard rock would by degrees sink so low as to allow a depth sufficient for the waters to flow without commotion. This will be evident by an inspection of fig. 2, the stratum, 3, being soft shale. The inclination of the strata and the soft character of the rocks through which the river flows at the falls, are the causes of that apparently miraculous tranquillity which is observed to take place immediately after the river has plunged down the precipice. This sudden repose surprised me more than the falls themselves.

[ocr errors]

Art. VI.-On certain Improvements in the Construction and

Supply of the Hydro-oxygen Blowpipe, by which Rhodium, Iridium, or the Osmiuret of Iridium, also Platinum in the large way, have been fused; by ROBERT HARE, M.D., Professor of Chemistry in the University of Pennsylvania. (Communicated by the Author.)

Having observed while I was a pupil of my predecessor, Dr. Woodhouse, in the year 1801, that a jet of hydrogen when inflamed in atmospheric air, of which only one-fifth is oxygen, produced a heat of pre-eminent intensity, I was led to infer that in combining with pure oxygen, the gas in question ought to produce a temperature at least five times as great. This led to the contrivance of two modes of producing a jet consisting of a mixture of hydrogen with oxygen. Agreeably to one mode, the gaseous currents meeting like the branches of a river, were made analogously to form a common stream. This object was accomplished by means of perforations drilled in a conical frustum of pure silver, so as to converge until met by another shorter perforation, commencing at the opposite surface, and so extended as to join them at the point of their meeting. The other mode was that of causing one tube to be within another, so as to be concentric; the outer tube being a little the longer of the two, the latter being employed for hydrogen, the former for oxygen.

In the year 1814, this last mentioned mode was improved, so as to have the means of securing, by adjusting screws, the concentricity of the tubes, and varying the distance of the orifice of efflux of the inner tube from that of the other.

The constructions employed in 1801, were described and published in a pamphlet, and afterwards republished in Tilloch's Philosophical Magazine, Vol. xiv, and in Annales de Chimie, Vol. xlv. At the same time an account was given of the fusion of pure lime and magnesia, and of the fusion of platinum. Subsequently in a paper published in the Transactions of the American Philosophical Society, it was mentioned that I had volatilized platinum.

About the year 1811, Professor Silliman, in a memoir read before the Connecticut Academy of Sciences, gave an account of a series of experiments, in which the experiments which I had performed were repeated, and many additional fusions made. I had adverted to the intensity of the light produced during the exposure of lime to the flame. Alluding to the heat and light, my words were, “the eyes could not sustain the one, nor the most refractory substances resist the other." The intensity of the light was still more insisted upon by Silliman.

My experiments were also repeated by Mr. Rubens Peale, during many successive years, at the Philadelphia Museum, for the amusement of visitors.

About the year 1813–14, it was ascertained, at the laboratory of Dr. Parrish, that a bladder being supplied with a mixture of hydrogen and oxygen, in due proportion, and punctured by a pin, while subjected to compression, on igniting the resulting jet, the gas within the bladder did not explode. Of course a burning jet of flame thus created, was found competent to produce, while it lasted, the same effect as when otherwise generated by the same gaseous mixture.

Soon after this result was obtained, Sir Humphrey Davy discovered, that if a lamp flame be completely surrounded by a gauze of fine wire, it may be introduced into an inflammable gaseous mixture without causing it to explode. This was ascribed to the refrigerating influence of the metal, keeping the gaseous mixture below the temperature requisite for inflammation. Hence it was inferred, that if a mixture of hydrogen and oxygen, while condensed within a suitable receiver, were allowed to escape through a capillary metallic tube, so as to form a jet, this might be made to burn without communicating ignition to the portion remaining in the receiver.

By means of an apparatus contrived agreeably to this idea, Dr. Clark of Cambridge, England, repeated the experiments, made many years before by Silliman and myself, without any other reference to ours, than such as was of a nature to do injustice. An exposition of the invalidity of Dr. Clark's pretensions to originality was made in Silliman's Journal for 1820, vol. ii, and in Tilloch's Philosophical Magazine, for 1821, vol. Ivii.

The light produced by the hydro-oxygen flame with lime having been observed by Lieutenant Drummond, of the British navy, was ingeniously proposed by him, as the means of illumination in light-houses, and in consequence, has been subsequently used as a substitute for the solar rays, in an instrument known as the hydro-oxygen microscope, which is a modification of that which has been called the solar microscope. The name of Drummond light has consequently been given to a mode of illuation, which I originally produced as above stated.

The instrument which was used by Professor Silliman and by Rubens Peale, was that above described as having two perforations meeting in one. In this form it was, I believe, employed by Dr. Hope, of Edinburgh, and Dr. Thompson of Glasgow, who both treated it as my contrivance, anteriorly to the publication of Dr. Clark's memoir.

The other form, consisting of two concentric pipes, was modified by a Mr. Maungham, with the view of producing a lime light for the microscope above alluded to. When I saw Mr. Maungham at the Adelaide gallery in 1836, he treated this instrument as mine, in another form. I was surprised afterwards to learn that he had obtained a premium for this modification from the British Society for the Encouragement of Arts, without any allusion to the original inventor.

After my return from Europe in 1836, I was very much in want of a piece of platinum of a certain weight, while many more scraps than were adequate to form such a piece were in my possession. This induced new efforts to extend the power of my blow pipe; and after many experiments, I succeeded so as to fuse twenty-eight ounces of platinum into one mass.

Although small lumps of platinum had been fused by many operators, with the hydro-oxygen blow pipe, as well as myself, it had not, up to the year 1837, been found sufficiently competent to enable artists to resort to this process. I am informed by Mr. Saxton, that some efforts which were made while he was in London were so little successful, that the project was abandoned. There was an impression that the metal was rendered less malleable when fused upon charcoal, as in the experiments alluded to. This is contradicted by my experiments, agreeably to which fused platinum is as malleable as the best specimens obtained by the Wollaston process, and is less liable to flake. The celebrated Dr. Ure, on seeing the platinum in the form of wire, of leaf, and plate, said that there was no one in Europe who could fuse platinum in such masses. He also alledged that it had been found so difficult to weld platinum, that no resort was had to that process. In this I concur, having had the welding tried by a skillful smith, both with a forge heat, and with a heat given by the hydro-oxygen blow pipe. An incorporation of two ingots was effected on their being hammered together, when heated nearly to fusion; but on hammering the resulting mass cold, a separation took place along the joint by which the ingots were united.

The difficulty seems to arise from the rapidity with which the platinum becomes refrigerated. It seems to have a less capacity for heat than iron, and, not burning in the air as iron does, has not the benefit of the heat acquired by iron from its own combustion with atmospheric oxygen.

Lately, by means of the instrument and process which it is my object here to describe, I have been enabled to obtain malleable platinum directly from the ore, by the continued application of the flame. From some specimens of platinum I have procured as much as ninety per cent. of malleable metal. The malleability is not inferior to that of the best specimens obtained by reducing it to the state of sponge, through the agency of aqua-regia and sal-ammoniac. There is, however, a greater liability to tarnish, arising, probably, from the presence of a minute portion of palladium.

Of the fusion of iridium and rhodium, I have already given an account in the Bulletin of the American Philosophical Society, which was subsequently embodied in an article in this Journal for October last, 1846.*

It remains now to give an account of the apparatus employed in the fusion of platina on a large scale.

Fig. 1 represents the association of fifteen jet pipes of platinum with one large pipe, B, D, at their upper ends, so that their bores communicate, by means of an appropriate brass casting, with that of the large pipe, the joints secured by hard solder. Their lower extremities are made to protrude about half an inch from a box, A, of cast brass, their junctures, with the appropriate perforations severally made for them, being secured by silver solder. They come out obliquely in a line along one corner of the box, an interval of about a quarter of an inch alternating with each ori ice. By means of flanges, the brass box is secured to a coniical frustum of copper, fig. 2, so as to form the bottom thereof, while the pipe, extending above the copper case, is screwed to a hollow cylinder of brass, A, fig. 3, provided with two nozzles and gallows screws, g, g, for the attachment of appropriate hollow knobs, to which pipes are soldered, proceeding from the reservoirs of oxygen and hydrogen. Cocks are interposed by which to regulate the emission of the gases in due proportion.

In connecting the pipes conveying the gases with the brass cylinder, A, fig. 3, care should be taken to attach that conveying oxygen to the upper nozzle, while the other, conveying hydrogen, should be attached to the lower nozzle ; since, by these means their great difference in density tends to promote admixture, which, evidently, it must be advantageous to effect.

The object of surrounding the jet pipes with water, by means of the copper box,t is to secure them against being heated to such a degree as to cause the flame to retrocede and burn within them, so as finally to explode within the cylinder, A, , g, fig. 3. It is preferable to add ice or snow to the water, in order to prevent undue heat.

Fig. 4 represents a movable platform, A, of cast iron, wholly supported upon the point of the iron lever, D, B, which is curved towards the extremity under the platform, so as to point upwards, and to enter a small central conical cavity made for its

* Since published in the Revue Scientifique at Paris.

1 Since ihe engraving was made, I have preferred to use water-tight boxes, with gallows screws and nozzles, situated one near the bollom on one side, the other on the opposite side near the top. By means of the lower nozzle, a pipe is altached, communicating with a head of cold water, the other being so situated as to carry the water into a waste pipe, or large tub; a circulation may be kept up dur. ing the whole time that the operation is going on.

As a support, a brick kaolin is nsed, having an oblong ellipsoidal depression on the upper face for the reception of the metal to be fused.

« AnteriorContinuar »