THE PHYSICAL PROPERTIES OF METHYL-ALCOHOL. 519 



tube through a long-necked stop-cock funnel until the metal comes almost close 

 to the necks of the two cups. Supposing now two specimens of methyl-alcohol 

 to be operated upon, a small quantity of one is introduced into, say, the left 

 limb, boiled there to expel its air, the stopper inserted, a little mercury poured 

 into the cup, a little of the respective alcohol added, and the cup closed by 

 means of a small glass cap fixed on by means of good india-rubber tubing, so 

 that the two glass rims touch each other inside. The india-rubber is well wired 

 on both sides. In a similar manner the right limb is charged with the other 

 specimen, and the greater part of the mercury of the middle tube syphoned out. 

 The charged tensiometer is suspended in an exactly vertical position within a 

 large square water-bath, the front and back of which consist of plate glass, and 

 connected air-tight with the bottle, and thus indirectly with the manometer. 

 A standard thermometer, from Geissler of Bonn, suspended in the water-bath, 

 gave the temperatures. The higher temperatures were established by means of 

 a properly adjusted mixture of hot and cold water, and maintained by means 

 of steam sent into the bath through two block-tin pipes which pervaded the 

 bath in its entire height. By properly regulating the current of steam, and 

 perpetual agitation of the water in the bath, we soon learned to keep even the 

 highest temperatures constant to within ±0 o- l C. Immediately before and 

 immediately after each series of experiments the zero correction of the ther- 

 mometer was ascertained, to be allowed for in the ultimate record. To test 

 the thermometer for the exactitude of its calibration, we constructed an air- 

 thermometer — pretty much on the Jolly principle — and determined the true 

 temperature-values for a large number of the marks on the Geissler standard 

 by several series of experiments. As we had no real cathetometer at our 

 disposal, we were not able to bring down the uncertainty of the temperature 

 values, as determined by the air-thermometer, to less than o, l to o- 2 C, but 

 within these limits the Geissler instrument (as corrected for the zero displace- 

 ment) proved correct. We subsequently procured a large thermometer from 

 Mr Casella (London), which was made by him out of a long capillary tube 

 which we had calibrated most thoroughly by means of Rudberg's method. This 

 standard thermometer, by its calibration table, gives temperatures correctly to 

 within about 0°'02 C. ; but, unfortunately, before we had a chance of using 

 it for standardising the Geissler instrument, the scale of the latter (which is 

 on a separate glass strip enclosed with the thermometer stem within a glass 

 jacket) became loose, and we could not manage to refix it in absolutely its 

 original position. 



The millimetre scales on all our instruments we made ourselves by means 

 of an excellent screw-engine from Bianchi of Paris, which Professor Tait 

 kindly lent to us. 



In the numerous preliminary tension determinations, which we referred to 



