234 MORRIS LOEB 



centration of the solution at the moment of observation, I re- 

 quired two data: the amount of iodine and of solvent intro- 

 duced into the bottle (which I obtained from the weighings 

 of the sealed tubes and from the known strength of the solu- 

 tion with which they were filled) ; and secondly, the amount 

 of solvent which had assumed the gaseous state, and must 

 therefore be deducted from the original quantity in solution. 

 This was easily calculated by the regular gasometric formula, 

 the volume of gas being 270 cc., the temperature being known, 

 and the pressure being that of the vapor of the pure solvent, 

 less the depression formed by the direct observation. I found 

 that I could employ the vapor tensions of pure ether and car- 

 bon bisulphide from tables calculated from Regnault's meas- 

 urements, as a few direct comparisons proved that they agreed 

 with those given by my apparatus, within the limits of ex- 

 perimental error. The expression for the amount of solvent 

 remaining in the solution at the moment of observation is 

 therefore 



[809] g70.M(/-g) 



760(l+aO 



where a = grams of solvent originally present ;/= the tension 

 at the temperature t of the pure solvent, expressed in milli- 

 metres of mercury; 0=the depression of tension, also in terms 

 of millimetres of mercury; w= weight in grams of 1 cc. of the 

 vapor under standard conditions. Now if b = the weight of io- 

 dine in the solution, and p - the ratio of solvent to iodine 



b 



I. p- 



270 . w . (f-e) 

 760 . (1+ctf) 



The concentration being thus ascertained, the calculation 

 of the molecular weight of iodine was made according to the 

 formula 



