118 RICHARDS — THE ATOMIC WEIGHT OF NITROGEN. [April 7, 



weight of the nitrogen, since this is merely the remainder left after 

 subtracting that of the bromine and the hydrogen. Hence, Stas's 

 estimate of the atomic weight of nitrogen is probably too high — 

 how much too high it is impossible at once to decide. Some of the 

 possible impurities have so powerful a color that an inappreciable 

 weight of them might darken visibly an otherwise pure sample of 

 salt ; but an inappreciable weight could not affect the combining 

 proportion, hence the error may be negligible. 



In any case it is obviously well that Stas's experiments on 

 ammonic bromide should be verified ; and the repetition was under- 

 taken by Scott. His ammonium preparation was purified, as he 

 states, by drastic methods, and was beautifully clear and colorless. 

 There is little doubt that, so far as the ammonium was concerned, 

 the salt was purer than Stas's. Unfortunately, however, in his 

 anxiety to purify the ammonium, Scott evidently neglected to 

 purify adequately the bromine which he combined with it. His 

 own results prove this fact indubitably, for he found on the aver- 

 age^ that 107.93 parts of silver combined with only 79.943 parts of 

 his bromine,^ a figure perceptibly lower than the most probable 

 value, 79.955. This latter value, computed from Stas's work, has 

 been repeatedly verified in the Chemical Laboratory of Harvard 

 College during the last twelve years with only very slight variations. 

 In order to show how definite the figure is, there is given below a 

 table of all our most refined recent work on this ratio. ^ 



1 Neglecting one imperfect experiment,/. Chem. Soc. Trans., 79, 147 (1901). 



2 Even this weight of, bromine may have b;en too high, since Scott apparently 

 overlooked the danger of the inclusion of water by the argentic bromide (Proc. 

 Am. Phil. Soc, 1903, 28). The fused substance is the only safe standard of 

 reference. In this connection it should be noted that an impurity in Scott's 

 silver would have caused an error in the same direction, Scott seems to have 

 taken more pains with his silver than with his bromine, although indeed he con- 

 demns on the basis of a single analysis a method of fusing it which many others 

 have found satisfactory (/. Chem. Soc. Trans., 79, 15, 1901). 



3 Clarke's similar table, Recalc, p. 46 (1897), is necessarily incomplete and 

 includes some imperfect preliminary results, besides containing several minor 

 mistakes in calculation. 



