518 PROFESSOR DITTMAR AND MR C. A. FAWSITT ON 



Our apology for publishing these in the following section is the conviction that 

 the numbers, though not what we would wish them to be, are probably better 

 approximations to the truth than those given in the present handbooks of 

 chemistry. 



The Tension-Curve of Methyl- Alcohol. 



In regard to it our programme from the first was limited in the sense that 

 we did not intend to go beyond about 760 mm. as our maximum value. 



The apparatus which we used is substantially the same as that which one of 

 us employed many years ago for comparing the vapour tensions of the two fatty 

 esters C 3 H 6 2 . # Figure 2 on Plate XXXIII. shows the form which it assumed 

 on the present occasion. The part which receives the liquids to be operated 

 upon consists of a glass U-tube A, with a vertical tube soldered in between the 

 two limbs. The two side tubes have an inner diameter of about 1 centimetre ; 

 the section of the middle tube is about equal to those of the two side tubes 

 taken together. The side tubes are contracted somewhere near the upper end, 

 and a well-ground glass stopper is fitted into the neck of the cup at the top. 

 The exit end of the central tube communicates with a large bottle, and through 

 it with a syphon-barometer B. In the latter the close limb is so long that the 

 vacuum can be expanded into very much more than the customary volume. 

 This long limb terminates in a funnel-shaped cup, the neck of the funnel being 

 provided with a well-ground-in stopper. A mercury reservoir R, connected 

 with a short side-branch from the open limb by means of a long piece of capil- 

 lary india-rubber tubing, enables one to bring the two mercury-menisci into 

 convenient positions. A small air-pump constructed so that it may serve for 

 exhaustion or compression, and communicating more immediately with the bottle, 

 serves to establish the required degree of attenuation in the latter. The three 

 limbs of the W-tube and those of the manometer bear etched-in millimetre scales. 

 The close limb of the manometer, from the top clown to the lowest occurring 

 position of the meniscus, is calibrated so that the unavoidable residuum of air in 

 that limb can be determined by ascertaining the height of mercury supported 

 by the atmosphere at two widely different vacuum volumes. Before charging 

 the W-tube, a true zero plane for the three scales must be found by charging 

 the apparatus with mercury up to a little beyond the three nominal zero-marks, 

 making the limbs exactly plumb, and reading the three menisci in reference to 

 their respective scales. Supposing the zero in the middle tube to be taken as 

 the standard, this gives the corrections for the mercury columns in the two side 

 tubes. By means of the well-known artifices, it is easy to fill the bends of the 

 tensiometer with air-free mercury. More mercury is then run into the middle 



* Chem. Soc. Jour., [2], vi. 477; Annal. iJ. CJiem. u. Pharm., Suppl., vi. 313; Jahresb. f. 1868, 

 p. 500. 



