THALLIUM. 95 



Fi'om the foregoing results three values for the atomic 

 weight of thallium are calculable : 



From the sulphate TI = 204.169, rh .166 



From the chloride " =: 203.879, =b .126 



From the iodide " = 203.886, ± .054 



In 1873 Crookes,* the discoverer of thallium, published 

 his final determination of its atomic weight. His method 

 was to effect the synthesis of thallium nitrate from weighed 

 quantities from absolutely pure thallium. No precaution 

 necessary to ensure purity of materials was neglected ; the 

 balances were constructed especially for the research ; the 

 weights were accurately tested and all their errors ascer- 

 tained ; weighings were made partly in air and partly in 

 vacuo, but all were reduced to absolute standards; and un- 

 usually large quantities of thallium were employed in each 

 experiment. In short, no effort was spared to attain as 

 nearly as possible absolute precision of results. The details 

 of the investigation are too voluminous, however, to be cited 

 here ; the reader who wishes to become familiar with them 

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

 research is a model which other chemists will do well to 

 copy. 



The results of ten experiments by Professor Crookes may 

 be stated as follows. In a final column we may state the 

 quantity of nitrate producible from 100 parts of thallium. 

 The weights given are in grains : 



Thallium. ll/VO.^ -(- Glass. Glass Vessel. Ratio. 



497.972995 I12I. 851852 472.557319 130.3875 



293-193507 nil. 387014 729.082713 130.3930 



288.562777 971.214142 594.949719 130.3926 



324.963740 II42. 569408 718.849078 130.3900 



183.790232 1005.779897 766.133831 130.3912 



190.842532 997.334615 748.491271 130.3920 



195-544324 1022.176679 767.203451 130.3915 



201.816345 1013.480135 750.332401 130.3S97 



295.683523 1153.947672 768.403621 130.3908 



299.203036 1159.870052 769.734201 130-3917 



Mean, 130.3910, ± .00034 

 * Philosophical Transactions, 1873, P- 277. 



