MORRIS LOEB 



of the bottles, the iodine solution is placed, whilst the pure 

 solvent is put into the other. These liquids are contained in 

 glass tubes, drawn out at both ends into capillaries that make an 

 obtuse angle with the wider part. The tubes are first weighed, 

 then filled, closed before the blowpipe, and again weighed. 

 They contain about 3 cc. of liquid, pass readily through the 

 narrow necks of the bottles, and can be broken by moderately 

 shaking the bottles. Before this is done, however, the bottles 

 are closed with their stoppers smeared with deliquesced 

 phosphoric acid to insure a perfect joint and are placed in a 

 water-bath of constant temperature. The T-tube is now con- 

 nected with a two-necked Woulff's bottle, filled with colored 

 distilled water, and communicating by its second neck with an 

 air-pump. Air is exhausted, until the pressure within the appa- 

 ratus is diminished to an extent equivalent to the amount of 

 tension to be expected from the vapors of the liquids, and 

 the pinch-cock is then closed, so as to interrupt communica- 

 tion with the Woulff s bottle. The air-pump being discon- 

 nected, atmospheric pressure is restored in the WoulfFs 

 bottle, and on carefully opening the pinch-cock the water is 

 allowed to ascend halfway up the long tubes; the pinch-cock 

 is then closed, and the WoulfFs bottle removed. The appa- 

 ratus is thus converted into a very delicate differential mano- 

 meter, affording direct readings of the difference of pressure 

 in the two bottles in terms of water centimetres; for con- 

 venience, the two tubes are brought closely together (see 

 figure) and a scale is placed behind them. 



The apparatus is quite independent of changes in the at- 

 mospheric pressure; the change in capacity, caused on either 

 side by an alteration in the level of the water in the tubes, is, 

 moreover, so slight in proportion to the volume of air in the 

 bottles, that it can safely be neglected; the effect of capillarity 

 in the two tubes is equal and opposite, so that this too may 



