42 IV.- On a New Method of Determining the Tapour-pressures of Solids aid Liquids, and on the Vapour-pressure of Acetic Acid. By WILLIAM R.AMSAY, Ph.D., and SYDNEY YOUNG, D.Sc. I N determining the vapour-pressure of acetic acid, Regnault (MLmoires de I'dcadeinie, 1862, 26, 51-60) found at 0" numbers varying between 3.23 mm. and 4.9 mm., whilst Landolt (Annulen, Suppl. v1, 157) gave 7.6 mm. ; at lo", Regnault gave numbers differing as much as 6.3 and 8.2 mm., and at that temperature Landolt found 12.1 mm. ; at 1.5" the difference is still more striking, €or the pressure given by €henu (Annales de Chimie [3], 18, 226j is 7 mm., by Regnault 8.7 to 10.4 mm., and by Landolt 15.1 ; while at 14", Wullner (Pogy. Ann., 103, 529) observed a pressure of 15.7 mm. No one has attempted to account for these discrepancies, except Regnault, who supposed his variations t o be due to the presence of acetone when the vapour-pres- sure was high, and of water when low.In the course of an investigation '' On the Temperature of Volatili- sation of Solids (Trans. Roy. SOC., Part I, 18%, p. 37), a method of ascertaining the vapour-pressure of liquids, differing essentially from the one usually employed, was devised, of which the following i3 a description :- A is a vertical tube, closed at the top by an accurately fitting india- rubber cork perforated with two holes, through one of whichRAMYAY AND YOUNG ON VAPOUR-PRESSURES, ETC. 43 thermometer passes, the bulb of which is completely covered with cotton-wool, adhering closely when moist. Through the other hole is inserted a short narrow glass tube, drawn out to a point a t its lower end, and slightly curved so that the point touches the thermometer.To the other end of this tube is connected by india-rubber tubing a small reservoir, B ; the passage of liquid from B is controlled by means of a screw-clip. It is thus possible to allow liquid to enter the apparatus, trickling down the thermometer and soaking the cotton- wool. A t C a tube, 15 nim. in diameter, is sealed on to the vertical tube. The tube .C communicates with the condenser E ; near the poiut of junction an exit-tube, F, leads to a Sprengel pump. On one side of the exit-tube, a narrow tube, D, is sealed. This narrow tube is for the purpose of admitting air into the apparatus, and is closed by a short piece of india-rubber tubing and a screw-clip.The tube A may be heated either by hot water or paraffin, or it may be jacketed with a wider tube, as shown in the figure, and exposed to the vapour of any desired liquid. The condenser, E, may be cooled with a freezing mixture, especia,lly if the liquid is volatile. The actual experiment is performed by exhausting the apparatus as perfectly as possible with a Sprengel’s pump, to which a gauge is attached ; by unscrewing the screw-clip, liquid enters the apparatus, trickles down the thermometei-, and thoroughly moistens the cotton- wool. When a sufficient quantity has entered, the screw-clip is closed. The tube is then heated, and the temperature 2nd pressure noted as soon as they have become consbant. A little air is admitt,ed by means of the clip a t D, and the pressure and temperature again read off.When the supply of liquid on the cotton-wool has become exhausted, more of the liquid is admitted. This process is repeated until a snfficient number of observations have been taken. The results may he checked by beginning a t a high pressure, and gradually ex- hausting the apparatus with the pump, reading whenever convenient. We think that this process has advantages over the usual one, inasmuch as the temperature of the whole apparatus has not to be kept constant, and the pressure can be regulated as desired, and a great number of observations taken ; moreover, the extreme difficulty of introducing a liquid free from air into a barometer tube is avoided. We are induced to think that the presence of air and moisture is the cause of most of the discrepancies in the results obtained by different observers.This method is equally applicable to the determination of the vapour- pressure of solids, by substituting a cork perforated with one hole instead of two, and coating the thermometer with the solid, by dipping it repeatedly into the melted substance. The only precaution required is to avoid dipping the bulb E so deeply into the freezing-mixture as44 RAMSAY AND YOUNG: NEW METHOD OF DETERMINING to block the exit-tube by condensation of the solid. Results proving the accuracy of this process have already been communicated in the paper previously referred to. The results obtained by this process of determining vaponr-pressures agreed closely, in the case of water, with Regnnult's results.We are therefore confident that the following numbers for acetic acid closely approximate to the truth. Moreover, as will be pointed out in a, sub- sequent paper, the curve for acetic acid given by this process is abso- Vapour-pressure of Acetic Acid. Solid. Temp. - 5.68" - 0.60 + 1.85 2 -86 5 *32 6.30 6.41 6 -68 7 -09 7 *20 8 *40 8.50 8 -72 9 *16 10 *40 11 *39 11-70 12 -10 12 *20 12.60 13.30 13 -96 14 *30 14 -58 14.85 15 -15 15.40 15.60 15 .SO 16 -09 16.20 16.32 16 * 4 i Pres. --- 1 ' 3 mm. 1 *95 2 -35 2 '80 3 *30 3.70 3 -75 3 *85 4 *oo 4 -05 4.25 4.35 4 -60 4 -70 5.30 5 -75 6 -15 6 *05 6 *05 6 -65 6 -75 7.30 7 *20 7 -95 8 -00 8.40 8.75 8.55 8 -85 8.95 9 '10 9 *15 9 *45 Liquid. Temp. 2 '72" 4 -20 4.70 6.30 7 *06 7 '13 8 '54 8 *58 9 -70 10 *60 10.70 12 '30 13 *70 14 *20 14 *39 14 *72 14.90 15 '50 15 *60 15 -70 16 -75 17 *OO 18 *60 19'20 20 '10 20 *go 21.40 21 * 68 22 -05 22.40 23 'OC! 23 -40 25.60 27 *20 27 *30 31 *30 32-70 36 .l o --- Pres. --- 4 *OO mm. 4 -25 4.75 5.00 5 *25 5 - 4 4 5.95 5 .Y5 6 -20 6-50 6 '75 7.30 8 *10 8.30 8.45 8 '50 8.55 9 '10 9 *15 9 -35 10 *45 9-75 11 *10 11 -05 12 '00 12 -45 12 *65 12 *85 13 -05 12 *go 13 *65 13 -80 15 *95 16 -80 17 *45 21 *80 2z -90 28.30 Liquid. Temp. 36 -9' 40 '1 43 *8 48 '2 48 -5 49 '2 49 -65 50 *5 53-5 57 -4 59 -6 61 -8 68 '5 69 '1 71 -6 73 -2 76 -4 78 -8 79 -8 81 -65 83.4 83 -9 84 -6 87 -5 91 -4 94 -5 97 - 4 98 *6 100-6 103 -3 105 *45 107 -45 110 *4 112 -4 113 -4 114 *1 117.15 --- Pres. 28 *9 mm. 34 '3 41 -7 51 -3 51.*7 53 *7 55 -6 58'1 66 -7 78 -7 87.6 96 *3 127 * 5 131 '9 146.3 156 - 2 177 *3 194 -4 19Y -5 215 -2 228.0 236-3 242 *1 267 -8 307 *Y 344 -3 376 - 4 396 *3 425 *2 460 -3 501 '8 540 -0 587 *1 623 *8 642 -6 657 -5 717 -9THE VAPOUR-PRESSURES OF SOLIDS AND LIQUIDS. 45 lntely coincident with that obtained by the usual process, when air and moisture were rigorously excluded, and when an absolutely pure specimen was employed. These results, which are here arranged in order, mere obtained in eight different series, f o r each one of which the acetic acid was fractionated from a large stock. From the numbers, the following results were obtained by graphic interpolation; it may be interesting to compare them with results obtained by Regnaidt, by Landolt, and by Wiilluer.1 Rarnsar and Young. I Tcnip. P. (solid). 00.. ,. i 2.02 10. .. .. 5.19 20. . . . . 30.. . . . 40. . . . . 50. . . . . , 60.. . . . 70. . . . . , 80 . . . . . I 90.. . . . ' - - - - - - - - 100.. . . . - 110 .....I - P. (liquid). 3 -50 6 .34 11 -80 19 -90 34 *o 56 '2 88 -3 137 *1 202 '0 292 '8 416.5 582 -6 Regnault. Pres. 3.23- 4.89 6.30- 8.20 11 '58-13 '65 ~~ Landolt. Pres. - 7 . 6 12.1 18 *9 29 *1 44.1 66 .O 97 -4 142 -0 204 - 3 290 -6 408 -5 - Wiillner. Pres. 19 .o 30 -5 45 * 5 72 *o 107 -3 155'2 232 -9 346 *7 473 .o - Results are also given by Bineau: a t 15', 7.70 rnm. ; at 22", 14.5 mm.; at 32', 23 mm. ; and by Naumann (Annulen, 155, 325) at 7S0, 185 mm. I n conclusion, it may be pointed out that the correct boiling point of a liquid a t atmospheric pressure is best determined by wrapping cotton-wool, or if the liquid at>tacks that substance, a,sbestos, round the bulb of the thermometer. By this plan, even though the vapour limy be superheated, yet the liquid in contact with the thermometer bulb must be a t the true boiling poiiit, since it has a free surface of evaporation. It is to be hoped that future experimenters will adopt this method, for little confidence is to be placed in the results obtained in t,he usual way.