Extraordinary Hydraulic Performance at Woolwich Dock-Yard. A most interesting exhibition of hydraulic prowess recently took place in her majesty's dock-yard at Woolwich, where there is a floating caisson of large dimensions, from which it is occasionally necessary to remove the water. This has hitherto been accomplished by means of a pair of ten-inch pumps, fitted up in the best possible manner by an eminent engineering firm in London. These pumps have been worked by a party of thirty-two convicts, in two gangs of sixteen each, relieving each other at intervals of ten minutes, by which means the water has been pumped out in three hours and a half, the men at the end of that time being much distressed by their continued exertions, Mr. Walker (of Crooked-lane, King William street,) having offered to raise the required quantity of water in half the time, with half the number of hands, by means of his newly invented pump of which we gave an account in volume xl, page 307*, his proposal was made known to the Board of Admiralty, who immediately called upon Mr. Walker to fulfil his promise. Mr. Walker accordingly fitted up a pair of twelve-inch pumps worked by a rotary motion, which were completed and tried on the 20th of September last, under the superintendence of Captain Dennison, R. E., in the presence of Lord Adolphus Fitzclarence, Sir Francis Collier, Mr. Oliver Lang, and the principal authorities of the dock-yard, who seemed to take a lively interest in the experiment, as the speedy emptying of the caisson is to them a matter of great moment. The new pumps were manned by fourteen convicts (the same formerly employed in this work,) in two gangs of seven each, relieving each other at intervals of fifteen minutes. In one hour and fourteen minutes the required task was accomplished, the men being in no way fatigued! The quantity of water raised was about 3350 cubic feet, or 95 tons, lifted 13 feet high! The result of this trial created great astonishment among all present; Mr. Walker was warmly congratulated on having more than fulfilled his promise, and a full report of the trial was duly made to the Board.

By placing a second pair of Mr. Walker's improved pumps in the caisson, it may, in case of emergency, be emptied in half an hour by 28 hands, although with the former pumps 32 men could not accomplish that task in less than three hours and a half. It is always very desirable to have the power of quickly emptying the caisson, but under certain circumstances, in the event of fire, for instance, it is of the utmost importance to be able to do so.

Barometer Pump.

Ibid.

Colonel Everest also described an instrument called a barometer pump, for filling barometer tubes in vacuo. This was a single acting air-pump, so arranged as to exhaust the air from the tube to be filled, * See Journal of the Franklin Institute vol. iv, 3rd series, page 109.

while a capillary tube, dipping into a reservoir of mercury, and curved at the end next the tube, dropped the mercury into the tube as it rose above the bend, (after the exhaustion had been carried as far as possible,) by dipping a glass rod into the reservoir. The mercury as it comes into the tube is heated to a temperature sufficient to boil it, and it is desiccated by a bottle of strong sulphuric acid, which is made to communicate with the canal into which the tube to be filled, and the capillary filling tube are luted. Colonel Everest mentioned that the best material for the valves of an air-pump was the swimming bladder of a fish.-(Proc. Brit. Assoc.)

Lond. Athenæum.

Report on a Hydrogen Furnace for Vitrification, and other applications of Heat in the Laboratory. By the Rev. W. V. HARCourt. At the request of the British Association Mr. Harcourt had undertaken, some years since, to make experiments on vitrification. Dr. Faraday, in his experiments on glass, had the greatest difficulty in procuring perfectly homogeneous masses, arising, in most cases, from the almost impossibility of procuring a regulated heat in the ordinary furnaces. Mr. Harcourt, impressed with the advantages which might be gained for optical purposes, by procuring glasses formed by other salts and bases, instituted some experiments with a view of ascertaining this point. It was considered, that if a tribasic phosphate formed ed a glass, and the bibasic phosphate formed a glass, we should have, in all probability, glasses having different optical properties. Finding difficulty in proceeding with these experiments, at the heat given by ordinary furnaces, and the risk to which the platina crucibles were exposed, he was induced to try the effects of hydrogen burning in common air. Dr. Dalton was consulted on the construction of the first hydrogen furnaces, and he suggested the difficulty which was found to arise in practice-that hydrogen gas burning, through small orifices, with great pressure, would blow itself out. This difficulty was, however, overcome in the management of the apparatus brought before the Section. This apparatus consisted of an iron tube, in which the gas was generated by the addition of 15 ounces of zinc to three-quarters of a pint of oil of vitriol, and ten pints and a half of water. The gas produced was found to be in ten minutes under a pressure of 21 atmospheres, in sixteen minutes and a half under a pressure of 25 atmospheres, and in eighteen minutes under a pressure of 26 atmospheres. The gas was conducted into another cylinder, and from thence to the jets, over which was suspended a platina crucible. The gas being ignited at these jets, maintained, with the above charge, the platina crucible at a white heat for twenty minutes. Gems had been fused by the heat thus generated. Several kinds of jets were used, as it might be necessary to surround the crucible with heat, or only to apply the heat to the bottom of it. Experiments with this apparatus have been made upon the phosphates of antimony, ziuc, barytes, and cadmium: the results have not been, however, quite satisfactory. In some the striæ inter

fered with the transparency of the glass formed; and in the case of the monobasic phosphate of zinc, it was found that, to whatever heat the compound may have been exposed, the glass, thus formed, was deliquescent. The reading of this report was accompanied by some experiments with the hydrogen furnace in question, for the purpose of showing the intense heat which could be produced.

Dr. Faraday bore testimony to the advantages of this arrangement. He had found in all his experiments on glass, in which the elements were chemically combined, that crystalization took place. He regarded all common glass as examples of solution, rather than of chemical combination. Borate of lead, and sillicate of lead, if fused in small quantities, so that they cooled quickly, were transparent, but if fused in masses, which required a longer time, they were in a crystalline condition. Mr. Harcourt remarked, that in the monobasic phosphate of zinc, which was transparent when vitrified, the quantity of acid was probably exceedingly small, but this glass was striated.— Dr. Faraday said, that some of the purest specimens of American ice show similar striæ, although it was in a state of exceeding purity, yielding the purest of all water when liquified.-Some remarks were then made by Mr. Pearsall, on the action of hydrogen on platina. An experiment was named by Mr. Harcourt, in which a platina tube was destroyed by an attempt to fuse ultra-marine in it.-Prof. Liebig stated, that platina was soon fused if exposed to a charcoal fire, from the action of the silicon contained in the charcoal.-(Ib.)

Ibid.

Contributions to Actino-Chemistry.-On the Amphitype, a new Photographic Process. By Sir J. HERSCHELL.

At the end of my paper "On the Action of the Solar Spectrum on Vegetable Colors," communicated to the Royal Society, in 1842, a process is alluded to (in Art. 230,) by which positive pictures are obtained, having a perfect resemblance to impressions of engravings taken with common printers' ink. I had hoped speedily to have perfected this process so far as to have reduced it to a definite statement of manipulations, which would insure success. But, capricious as photographic processes notoriously are, this has proved so beyond even the ordinary measure of such caprice; and, having of late been able to give little or no time to this pursuit, I have thought it preferable to describe the process in a general way, and in a form in which I have found it frequently, and sometimes eminently successful; not so much for the sake of its results, which yet are not wanting in interest, or beauty, as for the curious and very complicated photographic habitudes of iron, mercury, and lead, which are concerned in their production, rather, in short, as a contribution to the newly created science of actino-chemistry, than to the photographic art. Paper proper for producing an amphitype picture may be prepared either with the ferro-tartrate, or the ferro-citrate, of the protoxide, or the peroxide, of mercury, or of the protoxide of lead, by using creams of

these salts, or by successive applications of the nitrates of the respective oxides, singly, or in mixture, to the paper, alternating with solutions of the ammonio-tartrate, or ammonio-citrate, of iron,* the latter solutions being last applied, and in more or less excess. I purposely avoid stating proportions, as I have not yet been able to fix upon any which certainly succeed. Paper so prepared and dried takes a negative picture, in a time varying from half an hour to five or six hours, according to the intensity of the light; and the impression produced varies in apparent force from a faint and hardly perceptible picture, to one of the highest conceivable fullness and richness both of tint and detail, the color in this case being a superb velvety brown. This extreme richness of effect is not produced except lead be present, either in the ingredients used, or in the paper itself. It is not, as I originally supposed, due to the presence of free tartaric acid. The pictures in this state are not permanent. They fade in the dark, though with very different degrees of rapidity, some (especially if free tartaric, or citric, acid be present,) in a few days, while others remain for weeks unimpaired, and require whole years for their total obliteration; but though entirely faded out in appearance, the picture is only rendered dormant, and may be restored, changing its character from negative to positive, and its color from brown to black, (in the shadows,) by the following process:

A bath being prepared by pouring a small quantity of solution of pernitrate of mercury into a large quantity of water, and letting the sub-nitrated precipitate subside, the picture must be immersed in it, (carefully and repeatedly clearing off all air bubbles,) and allowed to remain till the picture, (if anywhere visible,) is entirely destroyed, or if faded, till it is judged sufficient from previous experience; a term which is often marked by the appearance of a feeble positive picture, of a bright yellow hue, on the pale yellow ground of the paper. A long time (several weeks) is often required for this, but heat accelerates the action, and it is often complete in a few hours. In this state the picture is to be very thoroughly rinsed and soaked in pure warm water, and then dried. It is then to be well ironed with a smooth iron, heated so as barely not to injure the paper, placing it, for better security against scorching, between smooth clean papers. If then the process have been successful, a perfectly black, positive picture is at once developed. At first it most commonly happens that the whole picture is sooty, or dingy, to such a degree that it is condemned as spoiled, but on keeping it between the leaves of a book, especially in a moist atmosphere, by extremely slow degrees this dinginess disappears, and the picture disengages itself with continually increasing sharpness and clearness, and acquires the exact effect of a copper plate engraving on a paper more or less tinted with pale yellow. I ought to observe, that the best and most uniform specimens which I have procured have been on paper previously washed with certain. preparations of uric acid, which is a very remarkable and powerful photographic element. The intensity of the original negative picture

So commonly called, and sold as such, but as I am disposed to regard their composition, their chemical na nes would be ferro-tartrate and ferro-citrate of ammonia.

is no criterion of what may be expected in the positive. It is from the production, by one and the same action of the light, of either a positive, or a negative, picture, according to the subsequent manipulations, that I have designated the process, thus generally sketched out, by the term amphitype,-a name suggested by Mr. Talbot, to whom I communicated this singular result; and to this process, or class of processes, (which I cannot doubt when pursued will lead to some very beautiful results,) I propose to restrict the name in question, though it applies even more appropriately to the following exceedingly curious and remarkable one, in which silver is concerned. At the last meeting I announced a mode of producing, by means of a solution of silver, in conjunction with ferro-tartaric acid, a dormant picture brought out into a forcible negative impression by the breath, or moist air. The solution then described, and which had, at that time, been prepared some weeks, I may here incidentally remark, has retained its limpidity and photographic properties quite unimpaired during the whole year since elapsed, and is now as sensitive as ever, -a property of no small value. Now, when a picture (for example, an impression from an engraving.) is taken on paper washed with this solution, it shows no sign of a picture on its back, whether that on its face be developed, or not; but if, while the actinic influence is still fresh upon the face, (i. e. as soon as it is removed from the light,) the back be exposed for a very few seconds to the sunshine, and then removed to a gloomy place, a positive picture, the exact complement of the negative one on the other side, though wanting, of course, in sharpness if the paper be thick, slowly and gradually makes its appearance there, and in half an hour, or an hour, acquires a considerable intensity. I ought to mention that the "ferro-tartaric acid" in question, is prepared by precipitating the ferro-tartrate of ammonia (ammonia-tartrate of iron,) by acetate of lead, and decomposing the precipitate by dilute sulphuric acid.

P. S.-When lead is used in the preparation of amphitype paper, the parts on which the light has acted are found to be in a very high degree rendered water-pooof.-( 1b.)

Ibid.

Workshop Micrometer.

Mr. Whitworth then exhibited an instrument for measuring bodies to a very minute degree of accuracy. It consisted of a strong frame of cast-iron, at the opposite extremities of which were two highly finished steel cylinders, which traversed longitudinally by the action of screws one-twentieth of an inch in the thread; these screws were worked by two wheels, placed at opposite extremities of the frame, the larger of which had its circumference divided into five hundred equal parts; the ends of the cylinders, at the places were they approached each other, were reduced to about a quarter of an inch, and their hemispherical ends were highly polished. To measure with this instrument, the large circle was brought to its zero, and the body