54 THE ATOMIC WEIGHTS. 



With the help of these molecular weights, we are now able to com- 

 pute seven independent values for the atomic weight of silver. 



First, from (10) and (20) Ag 107.1 1 1, db .0106 



Second, " (u) " (21) " = 107.378,^.0837 



Third, " (12) " (22) " = 106.921,^.0278 



Fourth, " ( 8 ) " (23) " = 107. 102, .0092 



Fifth, " (13) " (24) " = 107.122, .0050 



Sixth, " (14) " (25) " =107.113, dr. 0079 



Seventh, " (15) " (26) " = 107.091, dr .0062 



General mean Ag = 107. 108, dr .0031 



It is noticeable that five of these values agree very well. The second 

 and third, however, diverge widely from the average, but in opposite 

 directions ; they have, moreover, high probable errors, and consequently 

 little weight. Of these two, one represents little and the other none of 

 Stas' work. Their trifling influence upon our final results becomes 

 curiously apparent in the series of silver values given a little further 

 along. 



When we consider closely, in all of its bearings, any one of the values 

 just given, we shall see that for certain purposes it must be excluded 

 from our general mean. For example, the first is derived partly from 

 the ratio between silver and potassium chloride. From this ratio, the 

 atomic weight of one substance being known, we can deduce that of the 

 other. We have already used it in ascertaining the atomic weight of 

 silver, and the value thus obtained is included in our general mean. 

 But if from it we are to determine the molecular weight of potassium 

 chloride, we must use a silver value derived from other sources only, or 

 we should be assuming a part of our result in advance. In other words, 

 we must now use a general mean for silver from which this ratio with 

 reference to silver has been rejected. Hence the following series of silver 

 values, which are lettered for reference : 



A. General mean from all eight 107.108, dr .0031 



B. " excluding the first 107.108, dr .0032 



C. " " second 107.107, .0031 



D. " third 107.1 IO, rfc .0031 



E. " " fourth 107. 109, dr .0033 



F. " " fifth 107.099, dr .0039 



G. " sixth 107.106, dr .0034 



H. " seventh .... 107.113, dr .0036 



We are now in a position to determine more closely the molecular 

 weights of the haloid salts which we have already been considering. 



For silver chloride, still employing the formula for the probable error 

 of the last term of a proportion, we get the following values : 



