GOLD. 109 



Of the foregoing values the first one, which is derived from Berzelius' 

 work, should certainly be rejected. So also, apparently, should the eighth 

 and ninth values. Excluding these, values 2 to 7, inclusive, give a gen- 

 eral mean of Au = 195.743, .0049. With = 16, this becomes Au = 

 197.235. Probably these values are more nearly correct than those which 

 include all the determinations. 



The ninth value in the list given above represents Mallet's comparisons 

 of gold directly with hydrogen, and is peculiarly instructive. In Mal- 

 let's paper the other determinations are discussed upon the basis of 

 O = 15.96, which brings them more nearly into harmony with the hydro- 

 gen series. The great divergence shown in this recalculation is due to 

 the new value for oxygen, 15.879, and its effect upon the atomic weights 

 of silver, bromine, etc. The former agreement between the several series 

 of gold values was therefore only apparent, and we are now able to see 

 that concordance among determinations maybe only coincidence, and 

 no proof of accuracy. It is probable, furthermore, that direct compari- 

 sons 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 determinations of atomic weights hitherto made by the hydrogen 

 method. 



