MOLECULAR WEIGHT OF IODINE 231 



Two liquids at once presented themselves as the appropriate 

 solvents, ether and carbon bisulphide; they both have a con- 

 siderable vapor tension, and they may be considered as typi- 

 cal of the two kinds of solvents for iodine. For, whereas 

 many iodine solutions show impure tints, that in ether is of a 

 deep reddish-brown, and that in carbon bisulphide of a pure 

 violet. It was not so easy to find a proper 

 apparatus, as Raoult's is quite inap- 

 plicable. He operates in the Torricellian 

 vacuum, and has merely to note the com- 

 parative heights of the mercury when 

 the solution and the pure solvent are 

 introduced above it. In the case of 

 iodine, all contact with mercury must 

 obviously be avoided. After various 

 attempts, the following apparatus was 

 devised, which is an adaptation of 

 Regnault's manometer to the [807] pres- 

 ent purpose. It consists of two bottles of 

 nearly equal capacity, provided with care- 

 fully ground, hollow glass stoppers. To 

 these stoppers, glass tubes are adapted, 

 60 cm. long, and of about 6 mm. bore, which are bent twice 

 at right angles, so that there is an ascending limb and a hori- 

 zontal piece of 10 cm. length each, and a descending limb, 40 

 cm. long, for each half of the apparatus. The lower ends of 

 these two tubes are connected with each other by means of 

 a T-tube, to which they are joined by short pieces of very 

 stout rubber tubing; the third end of the T-tube serves as a 

 communication with the exterior when needed, and carries a 

 rubber tube with pinchcock. The communication between 

 the two halves of the apparatus can also be interrupted by 

 means of a pinch-cock on one of the rubber joints. In one 



