176 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



Eejection .of the very doubtful values from ratios 1, 8 and 9 lowers 

 the mean to 197.19. The atomic weight of gold is probably not far from 

 197.2. 



The ninth or last value in the foregoing series represents Mallet's I'atio 

 between gold and hydrogen, and is peculiarly instructive. In Mallet's 

 paper the several ratios determined were discussed upon the basis of 

 = 15.96, referred to hydrogen as unity. This, on the oxygen scale, is 

 equivalent to H = 1.0025. On that basis the determination in question 

 agreed well with the others; but with 11 = 1.00779, the present value, it 

 is enormously raised. The former agreement between the several series 

 of gold values was therefore only apparent, and shows that concordance 

 among determinations may be only coincidence, and no real proof of 

 accuracy. It is probable, furthermore, that direct comparisons of metals 

 with hydrogen cannot give good measurements of atomic weights, for 

 several reasons. First, it is not possible to be certain that every trace of 

 hydrogen has been collected and measured, and any loss tends to raise 

 the apparent atomic weight of the metal studied; secondly, the weight 

 of the hydrogen is computed from its volume, and a slight change in the 

 factors used in reduction of the observations may make a considerable 

 difference in the final result. These uncertainties exist in all determina- 

 tions of atomic weights hitherto made by the hydrogen method. 



