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VI. Researches on the Atomic Weight of Thallium. Bg William Crookes, F.R.S. &c. 
Deceived June 18, — Head June 20, 1872. 
Contents. 
Page 
Introduction 277 
Section I. 
On the Determination of Atomic Weights . . 278 
Section II. 
Apparatus employed 280 
The Balances 281 
The air-balance 281 
The vacuum-balance 281 
Weighing in a vacuum 282 
Correction for pressure and temperature 284 
The AVeights 287 
Method of adjusting a set of weights 288 
The Glass 294 
Improved Sprengel vacuum-pump 295 
Section III. 
The Chemicals 296 
AVater 296 
Nitric acid 298 
Oxalic acid 299 
Sulphuric acid 300 
Carbonic acid 301 
Ammonia 301 
Hydrogen 302 
Thallium 302 
Preparation of commercially pure thallium .... 303 
a. From the flue-dust of pyrites-burners . . 303 
h. From iron pyrites 306 
c. From sulphur or pyrites in the wet way. . 307 
d. From the saline residues of salt-works . . 307 
e. From commercial hydrochloric acid .... 307 
f. From the mother-liquors of the sulpbate- 
of-zinc works at Goslar 307 
Page 
Preparation of chemically pure thallium 308 
Purification of thallium by fusion in lime .... 309 
Section IY. 
Processes and Hesults 310 
Process of the conversion of thallium into nitrate 
of thallium 310 
Obtaining a weighed quantity of thallium .... 310 
AVeighing the thallium and glass apparatus in 
a vacuum 313 
Conversion of the thallium into nitrate of thal- 
lium 314 
Weighing the nitrate of thallium and glass 
apparatus 316 
Weighing the glass apparatus 316 
Section Y. 
Calculation of the Hesults 317 
Density of atmospheric air 317 
Values of 10 + log A, 318 
Influence of vapour of water 319 
Values of 0-378 x §v t 319 
First weighing in air of ordinary density .... 320 
Second weighing in a rare atmosphere 320 
Calculation of vacuum-weight of glass apparatus 321 
AVeighing of glass apparatus and nitrate of 
thallium 322 
Ditto in a rare atmosphere 323 
Calculation of vacuum-weight of glass apparatus 
and nitrate of thallium 323 
First weighing in air of ordinary density .... 323 
Second weighing in a rare atmosphere 324 
AVeight of thallium 325 
Results 326 
TnE atomic weight of thallium 329 
Conclusion 330 
In June 1862, and in February 1863, I had the honour to lay before the Royal Society 
communications on the subject of the then newly discovered metal, Thallium. In 
these I gave an account of its occurrence, distribution, and the method of extraction 
from the ore, together with its physical characteristics and chemical properties ; also 
mdccclxxiii. 2 p 
