122 ABSOLUTE ATOMIC WEIGHT. 



Lamy, in 1863, obtained a mean 611 high, in 3 determin- 

 ations. 



Hebberling, in 1865, also made 3 determinations; the 

 range was nearly a thousand (923). 



All these determinations are simply worthless. 



Accordingly, the determinations of Lepierre establish 

 the atomic weight of thallium as 204, independent of any 

 work done by Crookes at any time, before or after the work 

 of Lepierre. 



We are now able to take up the work of Crookes for 

 separate and independent consideration. 



Crookes' Determinations of Thallium. 



Ad hominem: We have no access to the original publi- 

 cation of Crookes in the Philosophical Transactions for 

 1873, where it begins on page 277, according to Clarke's 

 Constants (1882, p. 95, and 1897, p. 185), the only record at 

 hand giving the weighings and ratios of Crookes. 



It may be interesting to the student to read the general 

 statement of Clarke from this record. The italics are ours. 

 The quotation may be read identically the same in both 

 editions of Clarke, of 1882, p. 95, and of 1897, p. 185. 



t{ In 1873, Crookes, the discoverer of thallium, published 

 " his final determination of its atomic weight. His method 

 il was to effect the synthesis of thallium nitrate from weighed 

 " quantities of absolutely pure thallium. No precaution 

 " necessary to ensure furity of materials was neglected; the 

 " balances were constructed especially for the research ; the 

 a weights were accurately tested and their errors ascertained; 

 " weighings were made partly in air and partly in vacuo, but 

 u all were reduced to absolute standards; and unusually large 

 tf quantities of thallium were employed in each experi- 

 "ment." 



" In short, no effort was spared to attain as nearly as 

 a possible absolute precision of results. The details of the 

 a investigation are too voluminous, however, to be cited here; 

 11 the reader who wishes to become familiar with them must 

 "consult the original memoir. Suffice it to say that the 

 " research is a model ivhich other chemists will do vvell to coS ' 



