TOLMAN. — ELECTROMOTIVE FORCE PRODUCED IN SOLUTIONS. 123 



of great importance since the slightest loss of iodine in the neighbor- 

 hood of either of the electrodes created a large potential difference 

 between them. The tubes were carefully annealed and were floated 

 in oil inside the rotator arms ; nevertheless, the end thrust produced 

 by the centrifugal force was great enough to break many tubes even 

 at speeds as low as five thousand revolutions per minute. 



With the hope of obtaining some material which would stand higher 

 speeds, a great many other materials for tubes were investigated, includ- 

 ing porcelain, paraffined paper and wood, celluloid, vulcanite, and steel 

 tubes lined with paraffine, sulphur, and enamel but none was found 



B 



F 



Figure 4. Rotator Arm and Solution Tube. ^ size. 



satisfactory. Tubes of vulcanite, which has a specific gravity only 

 slightly greater than water, practically floated in the steel arm without 

 danger of breakage, and many experiments were made with them. 

 There seemed, however, to be a distribution of iodine between the hard 

 rubber and the solution which made it very difficult to keep the iodine 

 concentration the same at the two electrodes, and they were finally 

 discarded in favor of glass. 



Figure 4 gives a detail of one of the tubes with its electrodes. The 

 tubes were annealed by carefully wrapping them in asbestos and heat- 

 ing in a large electric furnace to about 500° C. and then allowing the 

 furnace to cool, which took a day and a half. The electrodes were 

 platinum. The outside electrode G rested on the bottom of the tube. 

 The connecting wire had to be platinum-iridium in order to stand the 

 centrifugal force. This wire was insulated from the solution by a glass 

 tube which is slightly enlarged at M. On the enlargement M rests 

 the inner electrode H. N shows the cross section of a glass thimble 

 which is slipped down on to the electrode. A bubble of air was en- 

 trained in this thimble to allow fof temperature expansion, and to 

 provide a means of stirring the solution. Melted ceresin which had 



