BAXTER AND WILSON. — THE ATOMIC WEIGHT OF LEAD. 373 



containing lead nitrate, silver nitrate, and nitric acid of the concentra- 

 tion of these filtrates, was passed through several small filter papers, 

 which were then very carefully washed. In four cases, after incinera- 

 tion of the papers, there was found, —0.00001, +0.00002, -f 0.00003, 

 +0.00001 gram of residue, exclusive of ash. This correction is so small 

 that it is neglected in the calculations. In all the analyses the plati- 

 num boat behaved admirably, the loss in weight never amounting to 

 more than a few hundredths of a milligram. 



The balance used was a short arm Troemner, easily sensitive to a 

 fiftieth of a milligram. The gold-plated brass weights were carefully 

 standardized to hundredths of a milligram. All the weighings were 

 made by substitution with tare vessels as nearly like those to be 

 weighed as possible. 



Vacuum corrections : The values of the density of lead chloride as 

 given by various observers range from 5.78 to 5.805,^^ the mean of 

 the more accurate determinations being 5.80. This gives rise to 

 a vacuum correction of +0.000062 for each apparent gram of lead 

 chloride, the density of the weights being assumed to be 8.3. The 

 other vacuum corrections applied were silver chloride, +0.000071, and 

 silver, —0. 000031. 



All analyses which were carried to a successful completion are 

 recorded in the preceding tables. 



The close agreement of the averages of the two series is strong 

 evidence that no constant error, such as occlusion, affects the results. 

 Furthermore, in all, 19.55663 grams of silver produced 25.98401 grams 

 of silver chloride, whence the ratio of silver to silver chloride is 132.865, 

 a value in close agreement with the result 132.867 obtained by Richards 

 and Wells.20 Furthermore, the different samples, A, B, and C, all 

 give essentially identical results. 



It appears, then, that if the atomic weight of silver is taken as 107.93 

 (0 = 16.000), the atomic weight of lead is 207.19, nearly three tenths 

 of a unit higher than the value now in use. If the atomic weight of 

 silver is 107.88, a value probably nearer the truth than 107.93, lead 

 becomes 207.09, a number still much higher than that depending upon 

 Stas's syntheses, as is to be expected. 



"VVe are greatly indebted to the Carnegie Institution of "Washington 

 for assistance in pursuing this investigation, also to Dr. Wolcott Gibbs 

 and to the Cyrus M. Warren Fund for Research in Harvard University 

 for many indispensable platinum vessels. 



Cambkidge, Mass., October 18, 1907. 



^9 Landolt-Bornstein-Meyerlioffer, Tabellen. 20 Lqc_ (.jt 



