A tin pan of about live inches in diameter, and four inches deep, had a hole made in its bottom near one side, and in this hole was soldered a socket some what conical, which nearly fitted a barometer tube with which the experiments were to be made. This tube was about 36 inches long, and had a ball at one end about 11 inches diameter, the contents of which were nearly equal to those of the stem of the tube; some paper was lapped round the tube near the ball, and it was forced tight into the conical socket of the pan, so that the ball was within the latter, at such a height that it might be immersed in water. The tube and pan were then inverted, and the ball was filled with clean mercury, and the stem with distilled water fresh boiled. The tube was re-inverted, so that the ball and pan were uppermost; the lower end of the tube being shut by the finger, the water ascended into the ball, and the mercury occupied the tube. The lower end of the latter being then placed in a cistern of mercury. and released from the finger, the mercury and water descended, and the ball was left partly emp ty: being agitated in this position, and let stand some time, much air was extricated from the water; the tube was inclined as much as it could be, and again inverted, the air let out, and its place supplied with boiling water. It was again placed with the ball up permost, the end of the tube stopt, the pan filled with hot water which was made to boil by means of a lamp,the lower end of the tube being placed in the cistern, and released from the finger, the mercury descended into the cistern, but, upon the water in the pan being suf fered to cool, partly rose again into the tube. Much air was thus liberated, and more was got rid of by agitation, in the manner of the water-hammer, and by leaving it standing for some time erect, until at last I got it so free from air, that when I raised it upright, it supported a column of mercury 34inches high; and no vacuum was formed until it was violently shaken, when it fell clown suddenly and settled at 28.75 inches, but upon being inclined, a speck of air always remain ed, though, when it was expanded by a pillar of mer cury 27 inches high, this speck was not larger than a pin's head.
In this state, when th..c was perpendicular, I found the mercury to stand at 28.75 inches, the co lumn of water above it was about 61 inches, —_-: half an inch of mercury. The whole then being 29.25 inches when the stationary barometer stood at 29.4, the dif ference, or pillar supported by the elasticity of the steam 0.15 inch. The water in the pan was then heated exceeding slowly by a lawn, and stirred con tinually by a leather, to make the heat as equal as possible. The results are shown in the following table.
To determine the heats at which water boils when pressed by columns of mercury above 30 inches, a tube of 55 inches long was employed; one end was put through a hole in the cover of a digester, and made tight by being lapped round with paper, and within the digester the end of the tube was immersed in a cistern of mercury. A thermometer was fixed in another opening, so that the bulb was in the inside of the digester, and the stem and scale without; and the bulb was kept half an inch from the cover of the di gester by a wooden collar. The cover being fixed on tight, and the digester half filled with water, it was heated by means of a large lamp.
The air in the upper part of the digester expand ing by heat, the column of mercnry in the tube was considerably raised by that expansion before the water boiled. The air was let out, and the water heated to boiling; still, however, sonic air remained, for the mercury stood at 2131°. That deduction being made, the following table shows the heats and correspond ing elasticities.
In making these experiments, the digester was heated very slowly, and the heat was kept stationary as much as was possible at each observation, so that the whole series occupied some hours. The degrees
of elasticity were observed by my friend Dr. Irvine, whilst I observed those of the thermometer in all these experiments.
With the whole of the observations. I was, after all, by no means satisfied, as I perceived there were irregularities in the results which my more urgent avocations did not permit me to explore the cause of, and to correct.
fished, in the Memot•s , :t ments on the elasticity of steam, from the ietopei ture of 32° to that of 212°. The following are a few of the results, which are here compared with those of Mr. Watt and Mr. Robison: The following results were obtained by Dr. Robison by the different operations which he has described in the article Steam in his works.
The next experiments on the elasticity of steam were made by Mr. Bettancourt, an ingenious Spaniard, who communicated them in 1790 to the Academy of Sciences, who published them in the Memoires des &weans Etrangeres.
The following are some of the results reduced to English inches, and to Fahrenheit's thermometer: Mr. Bettancourt made similar experiments on the elasticity of the vapour of spirit of wine, and he found it at all temperatures equal to 21 times that of steam.
The next set of experiments on steam were made by Mr. Dalton about 1800, with a degree of accuracy and care, which gives them a high value. The result:; from 32° to 212° were obtained by direct experiment, but those from 212' to were obtained by calcu lation.
`: ro:ioWh3g is hir, own account of the method by ' they were made:— take a barometer tube perfectly dry, and fill it with mercury just boiled, marking the place where it is stationary; then having graduated the tube into inches and tenths by means of a file, I pour a little water, (or any other liquid the subject of experiment) into it, so as to moisten the whore inside; after this, I again pour in mercury, and carefully inverting the tube, exclude all air. The barometer, by standing some time, exhibits a portion of water, Sze. of one eighth or one-tenth of an inch upon the top of the mercurial column, because, being higher, it ascends by the side of the tube, which may now be inclined, and the mercury will rise to the top, manifesting a perfect vacuum from air. I next take a cylindrical glass tube, open at both ends, of two inches diameter, and fourteen inches in length, to each end of which a cork is adapted, perforated in the middle, so as to admit the barometer tube to be pushed through, and to be held fast by them; the upper cork is fixed two or three inches below the top of the tube, and is half cut away, so as to admit water, and to pass bv, its service being merely to keep the tube steady. Things being thus circumstanced, water of any temperature may be poured into the wide tube, and thus made to surround the upper part, or vacuum, of the barome ter; and the effect of temperature in the production of vapour within, can be observed from the depression of the mercurial columns. In this way, I have had water as high as 155° surrounding the vacuum; but as the highest temperatures might endanger the glass apparatus, instead of it I used the following:— Having procured a tin tube, of four inches in dia meter, and ten• feet long, with a circular plate of the same, soldered to one end, having a round tube in the centre, like the tube of a reflecting telescope, I got another smaller tube of the same length soldered into the larger, so as to be in the axis or centre of it; the small tube was open at both ends, and on this con struction, water could be poured into the large vessel to fill it, whilst the central tube was exposed to its temperature. Into this central tube, I could insert the upper half of a syphon barometer, and fix it by a cork, the top of the narrow tube also being corked; thus, the effect of any temperature under 212° could he ascertained, the depression of the mercurial co lumns being known by the ascent in the exterior leg of the syphon.