KRRORS IX PRECISION". 3! 



the mercuric oxide as determined by him to the exact 

 hundredth of a milligramme. 



This is as perfectly and absolutely the case that this series 

 of determinations, if true, is most marvelous and created a 

 suspicion of being manufactured. 



In the reduction by Mr. Hardin the atomic weight of 

 mercury is affected with from o to 6 hundredths above 200. 

 These atomic weights are published as the expression of the 

 weighings, and are so taken by the chemical public. 



Such data as these are not data of observation, for they 

 are not representing the stated weighings; they represent 

 imagination and not observed facts. 



It is true, Mr. Hardin has said this series is vitiated by 

 other experiments made with larger amounts; but these six 

 determinations still stand on record as data of actual experi- 

 mental determination. 



If we are to have true atomic weights, we must first blot 

 out all false statements of fact, all invented atomic weights, 

 from the records and publications. 



It is well known, that such calculation of decimals can 

 not be carried beyond the limit of precision. Every manual 

 on experimentation gives rules for such limitation, as may 

 be seen in Kohlrausch. 



v My method is perhaps the simplest, equally applicable in 

 all cases, ftls found in my Elements of Physics, p. 12 ; 1870. 



It consists in actually calculating the value sought from 

 the formula by using the actual data determined and also 

 modified by one unit in the last place. The difference 

 between the two values evidently is the variation for that 

 unit. 



In the case before us, we must bear in mind, that for a 

 given amount of oxide, the increase in mercury would 

 necessitate a decrease in oxygen given by difference. 



Accordingly, for the first determination, in which 262.23 

 milligrammes of the oxide gave 242.81 mgr. mercury and 

 by difference 19.42 mgr. oxygen, we calculate Hg both for 

 these weights and for 242. 82 and 19.41. We find a change in 

 Hg of o.i i. 



Accordingly, as lialf a. hundredth of a milligramme is the 



