102 



THE ATOMIC WEIGHTS. 



Levol's * estimation of the atomic weight under consideration can 

 hardl3^ have much value. A weighed quantity of gold was converted 

 in a flask into AuClg. This was reduced by a stream of sulphur dioxide, 

 and the resulting sulphuric acid was determined as BaSO^. One gramme 

 of gold gave 1.782 grm. BaSO^. Hence Au = 195.06. 



All tliese values may be neglected as worthless, except that derived 

 from Berzelius' K.,AuCl- series. 



In 1886 Kriissf published the first of the recent determinations of the 

 atomic weight under consideration, several distinct methods being re- 

 corded. First, in a solution of pure auric chloride the gold was }ire- 

 cipitated by means of aqueous sulphurous acid. In the filtrate from the 

 gold the chlorine was thrown down as silver chloride, and thus the ratio 

 Au:3AgClwas measured. I subjoin Kriiss' weights, together with a 

 third column giving the gold equivalent to 100 parts of silver chloride: 



An. AgCl. Ratio. 



7.72076 16.84737 45.828 



5.68290 12.40425 45-814 



3.24773 7.08667 45-828 



4.49167 980475 45-811 



3-47949 7-59300 45-825 



3.26836 7 13132 45-S32 



5.16181 11.26524 45.821 



4.86044 10.60431 45-834 



Mean, 45.824, ± .0020 



The remainder of Kriiss' determinations were made with potassium 

 auribromide, KAuBr^, and with this salt several ratios were measured. 

 The salt was prepared from pure materials, repeatedly recrystallized 

 under precautions to exclude access of atmosjiheric dust, and dried over 

 phosphorus pentoxide. First, its percentage of gold was determined, 

 sometimes by reduction with sulphurous acid, sometimes by heating in 

 a stream of hydrogen. For this ratio, the weights and percentages are 

 as follows, the experiments being numbered for further reference, and the 

 reducing agent being indicated. 



KAuBr^. 



1. SO.^ 10.64821 



2. SO, 4.71974 



3- H 7.05762 



4. H 4-49558 



5- SO, 8.72302 



6. SO, 7.66932 



7- SO, 7-15498 



8. H 12.26334 



9- II 7-10342 



.002S 



* Ann. Chim. Phys. (3), 30, 355. 1850. 



t Untersuchungen iiber das Atonigewicht des Goldes. Mi'mchen, 18S6. 112 pp., 8vo. 



