878 PROCEEDINGS OP THE AMERICAN ACADEMY. 



the loss of water and possibly of carbon dioxide from the ordinary form 

 of potash bulbs. We also found a single sulphuric acid tube entirely 

 insufficient to absorb all the water. Clearly, then, if we were to use this 

 method, an elaborate investigation of the form of apparatus, method of 

 procedure, and limits of error, was absolutely imperative. The use of 

 the oxalate, however, did not seem sufficiently promising to warrant the 

 necessary expenditure of time. 



After thus investigating the uranium compounds which seemed likely 

 to furnish a suitable basis for an atomic weight determination, anhydrous 

 uranous bromide, in spite of its disadvantages, seemed most likely to fulfil 

 the necessary requirements. As already mentioned, this compound oxi- 

 dizes with the greatest ease on exposure to moist air. It was necessary, 

 therefore, to devise apparatus which should preclude any possibility of 

 bringing the sublimed bromide in contact with the air of the laboratory 

 until it had been collected and weighed. After much experimenting 

 with different forms of apparatus, the ibllowing method was adopted. 



Preparation and Collection of Pure Uranous Bromide. 



The mixture of urano-uranic oxide and carbon was placed in a porce- 

 lain boat within the larger of two " telescoping " porcelain tubes. The 

 portion of the tube containing the oxide was heated in a Fletcher furnace, 

 and after thoroughly sweeping out the apparatus with dry nitrogen, a 

 mixture of dry nitrogen and bromine vapor passed over the oxide. 

 The sublimed bromide collected near the inner end of the smaller porce- 

 lain tube. The very efficient and elaborate desiccating apparatus which 

 served so well in the work on the atomic weights of cobalt and nickel, 

 was very kindly given by Dr. Baxter for use in this investigation.* 

 This apparatus , with slight modifications, was used for drying the nitro- 

 gen and bromide, and was connected by a ground glass joint with the 

 porcelain combustion tube. 



With this apparatus traces of air diffused through the annular joint 

 between the porcelain tubes, forming a coating of oxide on the inner 

 tube.f In the case of uranium, the oxide is found to be copiously mixed 

 with the sublimate also. This diffusion of air takes place even when the 

 outer end of the inner porcelain tube is nearly closed, thus making a 

 considerable outward current within the tubes. 



* For a full description of this apparatus see There Proceedings, 33, 124 

 (1897). 



+ In the case of cobalt and nickel this oxide was easily removed by subsequent 

 treatnoent, but in the present case removal was impossible. 



