■474 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



estimated by precipitation as silver chloride. Three series of experi- 

 ments are given, representing three distinct preparations, as follows : 



Series I. 

 Am.PtCle. Pt. Per cent. Pt. 



2.1266 .9348 43.957 



1.7880 .7858 43.948 



1.8057 .7938 43.960 



2.6876 1.1811 43.946 



4.7674 2.0959 43.963 



2.0325 .8935 43.961 



Mean, 43.876, ± .001 



Another portion of this preparation, recrystallized from water, of 

 1.4358 grm. gave 0.6311 of platinum, or 43.955 per cent. 



Mean, 44.001, ih .003 



If these series are treated as independent and combined, giving each 

 a weight as indicated by its probable error, and regarding the single ex- 

 periment with preparation II as equal to one in the first series, we get 

 a mean percentage of 43.907, ±.0009. On the other hand, if we regard 

 the twenty-two Experiments as all of equal weight in one series, the 



