RICHARDS AND ARCHIBALD. — ATOMIC WEIGHT OF CAESIUM. 451 



pliate, using in the second case a pure block-tin condenser, fitted to the 

 neck of a Jena flask. It was kept in Jena flasks, and used as soon after 

 distilling as possible. Portions were always tested with the nephel- 

 ometer * for the presence of chlorine. 



(b) Method of Analysis. 



Having now obtained pure material, it was essential to free the chlor- 

 ide from all traces of moisture without loss of a trace of chlorine. 



It was soon found that this condition is assured when the substance is 

 fused in a current of nitrogen and bottled in an atmosphere of dry air. 

 For this purpose the apparatus which has been employed in this Labo- 

 ratory to such advantage in determining other atomic weights is suitable 

 and convenient, — namely, the " bottling apparatus," devised first for 

 preparing and weighing pure magnesic chloride, f This device enables 

 the substance to be ignited in a boat contained in a tube of the hardest 

 glass or porcelain in the purest of dry nitrogen ; and the final transfer- 

 ence of the boat to the weighing bottle filled with dry air takes place 

 without an instant's exposure to the outside atmosphere. The platinum 

 boat, which had been freed from superficial iron in other investigations, 

 was boiled in several different portions of nitric acid, and finally hydro- 

 chloric acid. Afterwards it was scrubbed with clean round sand, washed, 

 ignited, and cooled in its own weighing bottle. Another weighing bottle, 

 containing an appropriate amount of metal, of the same weight and 

 volume as the first, was used as tare. The platinum boat was now 



B 



A__jOl _ c c 



D 



Figure 1. — Bottling Apparatus, Horizontal Section. 



A = weighing bottle. B = stopper of bottle. C C = bard glass tube. 



D = Platinum boat containing fused caesic chloride. 



weighed in its bottle, the weighing being done by substitution, and all 

 precautions used in recent work done in this Laboratory were strictly 

 followed. X This weight of tube and boat scarcely changed throughout 



* Richards, Proc. Am. Acad., 30, 385 (1894) ; Z. anorg. Chem., 8, 269 (1894). 



t Richards and Parker, These Proceedings, 32, 55 (1896); Z. anorg. Chem., 

 13, 81 (1896). 



t Richards, Proc. Am. Acad., 26, 240 (1891) ; 28, 1 (1893) ; 29, 55; 30, 369; 

 Z. anorg. Chem., 1, 150 (1892) ; 6, 441 (1893), etc. 



