550 Mr. F. B. Jewett on a New Method of 



sodium in this coating, and consequently the amount of 

 saturated vapour that Had filled the bulb, the tube (b) was 

 cracked off at some point (m), thus getting rid of the metal 

 remaining in (a) ; the bulb was then thoroughly washed out 

 with hot water until the washings failed to show an alkaline 

 reaction with phenolphthaline, and the amount of Na present 

 as NaOH in the washings determined by differential titration 

 with standardized N/10 • NaOH and N/10 * H 2 S0 4 solutions ; 

 this amount, together with the corrected volume of the bulb, 

 furnished the requisite data for finding the vapour-density. 

 As this process had to be repeated for every determination, 

 the making of a large number of observations was an ex- 

 ceedingly tedious matter. 



The above-described method was the one finally chosen for 

 sodium ; a number of methods depending upon the gravi- 

 metric determination of the amount of metal volatilized, 

 while giving good results for those metals which do not 

 oxidize easily at low temperatures, e.g. Cd, proved absolutely 

 useless in the case of sodium on account of the rapid oxidiza- 

 tion of the latter when in contact with the air. 



A difficulty which it was at first feared might render the 

 determination impossible at the higher temperatures, viz.., the 

 action of sodium on glass, was not encountered except when 

 the residual atmosphere contained or water-vapour, the 

 solvent action being apparently exhibited only for the oxide 

 or hydroxide ; aside from this fact the results obtained in 

 the presence of air w r ere so extremely erratic that all the 

 final determinations were made either in the presence of 

 oxygen or nitrogen. (The majority of the tests were made 

 with hydrogen, and as they gave consistent results the 

 accuracy of the process was not questioned at the time, 

 especially as the hydride, Na i H 2 , was not supposed to form 

 at pressures so reduced as those employed "*. Owing, how- 

 ever, to a peculiar brown metallic appearance of the deposit 

 in some instances, doubt was cast on the validity of this 

 assumption, so that while the great mass of chemical data 

 seems to weigh against the formation of the hydride, there 

 still remains the possibility that the density of the vapour, 

 calculated on the assumption that it consisted of free Na, 

 gave too low a result. This question can be easily settled, 

 however, by the employment of N, since the nitride, NaN 3 , 

 is not formed by the direct combination of Na and N f.) 



Some of the results are given in Table I., and the curve, 



* Roscoe & Schorlemmer, ' Treatise on Chemistry/ vol. ii. pt. i. p. 107. 

 f Bevichte, xxv. p. 2084 (1892) ; Zeit.f. anorg. Ch. u. p. 38 (1894). 



