A

To illustrate the principles of the saturation gauge, suppose two globes, A and B, fig. 1, connected by a bent tube containing mercury at a b, and placed in a bath in which they can be raised to any required temperature. Suppose a Torricellian vacuum to have been created in each globe, and twenty grains of water to have been added to A, and thirty or forty grains to B. Now, suppose the temperature to be slowly and uniformly raised around these globes; the water in each will go on evaporating at each temperature, being filled with steam of a density corresponding to that temperature, and the density being greater as the temperature increases. At last a point will be reached at which the whole of the water in globe a will be converted into steam, and at this point the mer

α

cury column will rise at a and sink at b; this is the saturation test, and the cause of its action will be easily seen. So long as vaporization went on in both A and B, and the temperature was maintained uniform, each globe would contain steam of the same pressure, and the columns of mercury, a and b, would remain at the same level. But so soon as the water in A had vaporized, and the steam began to superheat, the pressure on a would cease to remain uniform with the pressure on b, and the mercury column would at once fall, and thus indicate the difference. The instantaneous change of the position of the mercury is the indication of the point at which the temperature in the bath corresponds with the saturation point of the steam in A. To show the delicacy of this test, I may instance, that at 290° Fahrenheit, the mercury column would rise nearly two inches for every degree of temperature above the saturation point, as the increase of pressure arising from vaporization is about twelve times that arising from expansion in superheating at that point, and a similar difference exists at other temperatures.

The arrangement of the apparatus, as employed for experiment, varies according to the pressure and other circumstances of its use. Fig. 2 represents one of the arrangements which has been employed with success. It consists of a glass globe A of about seventy cubic inches capacity, in which is placed, after a Torricellian vacuum has been formed, the weighed globule of water; this is surrounded by a copper boiler B B, prolonged by a stout glass tube CC, enclosing the globe stem. This copper boiler forms the water and steam-bath through which the globe is heated, and in fact corresponds to the second globe B in the former figure. The fluctuating mercury column, or saturation gauge, is placed at the bottom of the tube C C, and the saturation point is indicated by the rise of the inner mercury column b, and the fall at the same time of the outer mercury column c. As soon as the whole of the water in the globe A is evaporated, there is an instantaneous rise of the inner mercury column to restore the balance of pressure, and that progressively with the rise of temperature.

As an auxiliary apparatus the boiler is provided with gas-jets, E, to heat it, and with an open oil bath G to retain the glass tubes at the same temperature as the boiler, and this oil-bath is placed on a sand-bath, and also heated with gas. A thermometer D registers the temperature, and a pressure gauge F the pressure of the steam; and a blow-off cock H serves to reduce the temperature when necessary. A number of results

b....

H

T

G

B

have already been obtained, but they are not yet sufficiently advanced to be made public. The following numbers have been, however, approximately reduced from the theoretical formula above, and the experimental results may illustrate the use of this method of research. The most convenient way of expressing the density of steam, is by stating the number of volumes into which the water of which it is composed has expanded. Thus one cubic inch of water expands into about 1670 cubic inches of steam at 212° Fahr., into 882 cubic inches at 251°, and into 400 cubic inches at 304°, and so on; in this way the following numbers have been computed :

These determinations at pressures varying from ten to fifty lbs. above the atmosphere, uniformly show a decided deviation from the law for perfect gases, and in the direction anticipated by Professor Thomson, the density being uniformly greater than that indicated by the gaseous formula. We hope, by the time of the next meeting of the Association, to be enabled to lay before the Section a series of results which will fully determine the value of superheated steam, and its density and volume as compared with water at all pressures, varying from that of the atmosphere to 500 lbs. on the square inch.

An Experimental Illustration of the Gyroscope. By ALEXANDER GERARD.

Description of the Granite Quarries of Aberdeen and Kincardineshire.

By ALEXANDer Gibb.

The author gives an account of the commencement, progress and present condition of the granite quarries of Aberdeenshire and Kincardineshire, particularly of those in the immediate neighbourhood of Aberdeen, giving an account of the chief uses to which the stone has been applied. He then proceeds to show the most economic methods of working, the drawing steam power required, the tools and number of workmen employed, with the improved methods of dressing the stone, and the various ornamental as well as useful purposes to which the stone has been applied.

On Gas Carriages for lighting Railway Carriages with Coal-gas instead of Oil. By G. HART.

The author proposes to have a reservoir of gas or a carriage constructed to carry gas and to accompany each train. He then proceeds to show how it may be conveyed to each carriage and burned in the ordinary way. Supposing a train to consist of two first, four second, and four third-class carriages, and fitted up with twenty-two Argand burners (twelve holes), the quantity of gas required for a journey of twelve hours would be 800 feet.

On Indian River Steamers and Tow Boats. By ANDREW Henderson. The author gave an account of their improved construction for light draft, capability for cargo, and fittings conducive to management in shallow rapid rivers, &c., and of the practical value of the dynamometer in showing the resistance of vessels in tow, at different speeds and loads, with the result of test-trials made in England.

On a Deep-sea Pressure Gauge. By HENRY JOHNSON.

The pressure gauge may, in its present form, be considered as a small hydraulic press; of which the ram is forced into the cylinder by the increasing pressure of the sea when sinking, and expelled by the expansion of the water in the cylinder when rising.

It consists of a small tube or cylinder having at one end a tap, through which water is admitted; the tap having in addition to the passage admitting water, a smaller passage for the escape of air. At the other end of the cylinder is a packing box, through which a round bolt or solid piston passes. A scale by the side of the piston contains the degrees of compression, and an index at the further end of the scale is drawn along the scale by the piston when forced by increasing pressure into the cylinder, and secured in its position by a spring taking hold on a toothed rack at the side of the scale, where it remains when the piston is pushed back by expansion of water in the cylinder to its former position.

The scale and index are protected by a tube screwed on to the cylinder, and the cylinder is protected from the risk of indentation by an outer tube.

In an experimental instrument the packing-box has remained water-tight under the application of a pressure of 400 lbs. to the square inch on the piston; so that the isolation may be considered sufficiently perfect, as in actual use this pressure on water in the cylinder would be counterbalanced by the external pressure of the ocean. As the amount of friction required to obtain this isolation is considerable, and may be affected by the screwing down the packing-box, it would be desirable that after any alteration of the packing-box the instrument should be suspended, and the amount of friction ascertained, by hanging on to the piston a weight sufficient to overcome the friction.

In ascertaining the pressure of water, the amount of friction overcome should be added to the compression indicated by the index, to obtain the total amount of pressure.

Some portion of the diminution of bulk will probably be occasioned by variation of temperature, and which causes a greater variation in bulk at high temperatureAs 4000 parts of sea-water at the temperature of 86° Fahr.,

contracted to 3986 parts at the temperature of 65°, being parts for 21°. While from the temperature of 65° to 35°, the diminution to 3977 parts was only at the rate of ........ 4000 parts for 30°. The contraction of the cylinder by variation of temperature counteracts the variation of water to a very small extent, being about th parts for 40° Fahr.

On Surface Condensation. By J. P. JOULE, LL.D., F.R.S. The author described the experiments he had made on this important subject. A peculiar arrangement he had introduced gave a very increased effect to a given surface. In this arrangement a copper spiral was placed in the water spaces. The spiral had the effect of giving the water a rotatory motion, and the water was thus compelled to travel over a larger surface than it otherwise would do.

On a Submarine Lamp. By Mr. KETTIE.

The principle on which the lamp is constructed and depends for action, is that arising from the discrepancy of the gravity of the two columns of air necessarily engaged, viz. the column of cold for supplying combustion, and the column of heated air ejected; and in the arrangement of the tubes, advantage is taken to foster the peculiar qualities of the respective columns; thus the cold being made to descend by the larger and outer tube, whose surface is exposed to the action of the water; while the heated or centre column is placed immediately over the powerful burner of the lamp.

The lamp may be made either of a globular or cylindrical form, the bottom being made of brass, with a large screwed opening for the admission of the Argand burner used; on the top of the globe is a brass cap, into which is screwed a strong copper

tube, in the centre of which is fixed another tube less in diameter, and so fixed that air may pass freely in the space between the two: the lower end of this inner tube has a trumpet-shaped termination, which enters into the globe, reaching within two inches of the top of the chimney of the Argand burner of the lamp. The upper ends of the tubes terminate in a sort of lantern-top, which is divided into a lower and upper compartment; from the lower compartment the larger tube conveys the air required by the lamp for effecting combustion; while through the upper compartment is discharged, by the inner or centre tube, the vitiated air as ejected from the lamp.

On a New Gas-burner. By the Abbé MOIGNO.

On an Automatic Injector for feeding Boilers, by M. Giffard.
By the Abbé MOIGNO.

On a Helico-meter, an Instrument for measuring the Thrust of the Screw Propeller. By the Abbé MOIGNO.

On an Application of the Moving Power arising from Tides to Manufacturing, Agricultural, and other purposes; and especially to obviate the Thames Nuisance. By the Abbé MOIGNO.

On the Performance of Steam-vessels. By Vice-Admiral MOORSOм. At the last Meeting of the Association, the author presented a paper in which some account was given of the 'Erminia:' he now presents further particulars of that vessel, with remarks on performance.

The performance at the measured mile, being the mean of four trips, was as follows:

:

From calculations previously made, it was anticipated that a speed of six knots would require 90 horse-power, and that the slip might be about 21 per cent. The resistance of the vessel at six knots in smooth water was first estimated by resolving the resisting surfaces into an equivalent plane surface, and deducing the specific resistance of form by an empirical application of the method of Don Gorges Juan. This gave 2763.5 lbs. It was, secondly, estimated by another empirical process, which I had found to answer within given limits of form, and was founded on Beaufoy's experiments. This gave a specific resistance of 1896 lbs. The pitch of a screw of 8 feet diameter, to produce a resultant thrust of 2763.5 lbs. at six knots, is 13:37. The pitch selected being 13 feet, the slip to balance should be 21:11 per cent. Then how comes the actual slip to be only 10·66 per cent.?

The answer to this is the key to the whole operation, and it is this:

The direct thrust of the screw under the actual circumstances of the trial was 2122 7 lbs., and the resultant was 1896 4 lbs., and the difference of the ratios of their square roots is 10:66.

But 1896 lbs. is also the specific resistance as estimated by the second method, and as the thrust calculated by an independent process comes out the same, within half a pound, the concurrence of the two seems to establish that as the actual resistance at the time of the trial. Such concurrence may not, however, be held to be conclusive.

There are two modes by which these results may be tested, the one analytical, the other synthetical.

I will begin with the first, and employ the other in elucidation. The effective power, or total resistance, from the actual power of 54.59 horse-power, or 1801470 lbs. at six knots, is 2961.67 lbs., which is thus distributed :

I have in this analysis, as in my former paper, classed under the general term "equivalent of slip," two distinct elements, which I must now separate.

The first is that portion of the effective power which overcomes the resistance of the water to the rotation of the blades of the screw, and which is sometimes called lateral slip." The second is that portion of the effective power which is employed in pushing back the water to obtain a fulcrum.

"

The absorbed power is composed of-1st, the friction of moving the machinery; 2nd, the additional friction of the load; 3rd, the back pressure (as we are dealing with a non-condensing engine) from the blast-pipes.

In order to give a clearer view of these elements, I will reverse them, and show the corresponding pressure upon the piston :

The pressure on the piston by the diagrams is 32:07 lbs., showing a difference of 0.37, which may be considered near enough.

Now, if it be said that this is an arbitrary classification not resting upon known data, I reply, not altogether so. I have lying before me diagrams of back-pressure from 3:45 lbs. per square inch on the piston, moving at 236 feet per minute, with a mean pressure of 67 56 lbs. to 12.3 lbs. per square inch on the piston, moving at 569 feet per minute, with a mean pressure of 65 lbs., the diameters of blast-pipes varying from 43 to 4 inches, and the relations of steam ports from 14 X 13 inches to 12X1 inches of area.

The 'Erminia's' blast-pipes were 4 inches in diameter, the steam ports 12×11, and the speed of piston 157 feet per minute, with a pressure of 32:07 lbs. per square inch in the cylinder.

The back-pressure of 4'64 lbs. which results from the analysis is therefore probable, and consistent with experience.

The next element of additional friction arising from the load, viz. 2'07 lbs. per square inch, is calculated upon the specific resistance of 1896 lbs., and may be dis