BAXTER. — A REVISION OF THE ATOMIC WEIGHT OF IODINE. 429 



to small diameter, was inserted into one end of the weighing tube. After 

 the weighing tube had been filled, the glass stoppers were inserted, the 

 tube was carefully wiped with a slightly damp " chemically clean " cloth, 

 and was allowed to stand in a desiccator for some time. It was then 

 weighed. Needless to say the weighing tube had been originally treated 

 as above before being weighed empty. Both weighings were made with a 

 counterpoise exactly similar to the weighing tube. 



In all but one of the experiments the weighing tube was broken during 

 the solution of the iodine, so that it was impossible to weigh the tube after 

 the experiment, and determine how much the glass was attacked by the 

 warm iodine. In one experiment, however, a loss in weight of 0.00032 

 gram was found. Whether or not this change was accompanied by the 

 evolution of a gas, the loss in weight must have been at least partially 

 due to combination of the iodine with the alkaline metals of the glass, with 

 the formation of soluble iodides which were dissolved by the solution of 

 sulphurous acid. Hence the error must have been considerably less 

 than three tenths of a milligram, if, as was necessarily the case owing to 

 breakage of the tubes, the first weight of the tube was used in determin- 

 ing the weight of the iodine. 



Immediately after being weighed, in order to avoid loss by volatiliza- 

 tion, the iodine was converted into hydriodic acid by means of pure 

 sulphurous acid. This acid was made by heating sulphuric acid with 

 metallic copper and collecting the sulphurous oxide in water, and then 

 distilling the sulphurous oxide from the solution into the purest water. 

 During this distillation any trace of halogen acid which might have had 

 its source in either copper or sulphuric acid must have been completely 

 eliminated, for it must have been almost wholly in the ionized condition. 



A considerable quantity of this sulphurous acid was poured into one 

 of the precipitating flasks, and the weighing tube, containing the iodine, 

 was introduced, after the lower stopper had been allowed to drop out of 

 tlie tube into the flask. The sulphurous acid immediately sealed the open 

 end of the tube so that no iodine vapor could escape. The other stopper 

 was then removed by means of a platinum wire, the wire was rinsed 

 into the flask, and the flask was quickly closed by means of its glass 

 stopper. Solution of the iodine in the sulphurous acid was hastened by 

 gently agitating the flask. Any iodine vapor which escaped from tlie 

 tube must have been instantly converted into hydriotic acid. After suf- 

 ficient time had been allowed for every trace of this hydriodic acid to be 

 absorbed by the solution, the flask was opened and the solution was 

 transferred to another precipitating flask, and a slight excess of the purest 



