GOLD. 105 



From the second and third of the ratios measured by Thorpe and 

 Laurie an independent value for the ratio Ag : Br may be computed. It 

 becomes 100 : 74.072, which agrees closely with the determinations made 

 by Stas and INIarignac. Similarly, the ratios Ag : KBr and AgBr : KBr 

 may be calculated, giving additional chocks upon the accuracy of the 

 manipulation, though not upon the purity of the original material 

 studied. 



Thorpe and Laurie suggest objections to the work done by Kriiss, on 

 the ground that the salt KAuBr^ cannot be completely dried without 

 loss of bromine. This suggestion led to a controversy between them and 

 Kriiss, which in effect was brief! 3^ as follows : 



First, Kriiss* urges that the potassium auribromide ordinarily contains 

 traces of free gold, not belonging to the salt, produced by the reducing 

 action of dust particles taken up from the air. He apjilies a correction 

 for this supposed free gold to tbe determinations made by Thorpe and 

 Laurie, and thus brings their results into harmony with his own. To 

 this argument Thorpe and Laurie t reply, somewhat in detail, stating 

 that the error indicated was guarded against by them, and that they 

 had dissolved quantities of from eight to nineteen grammes of the auri- 

 bromide without a trace of free gold becoming visible. A final note in 

 defense of his own work was published by Kriiss a little later.;}; 



In 1889 an elaborate set of determinations of this constant was pub- 

 lished by Mallet, § whose experiments are classified into seven distinct 

 series. First, a neutral solution of auric chloride was prepared, Avhich 

 was weighed off in two approximately equal portions. In one of tbese 

 the gold was precipitated by pure sulphurous acid, collected, washed, 

 dried, ignited in a Sprengel vacuum, and weighed. To the second por- 

 tion a solution containing a known wei^lit of pure silver was added. 

 After filtering, with all due precautions, the silver remaining in the fil- 

 trate was determined by titration with a weighed solution of pure hydro- 

 bromic acid. We have thus a weight of gold, and the weight of silver 

 needed to precipitate the three atoms of chlorine coml)ined with it ; in 

 other words, the ratio Ag., : Au : : 100 : x. All weights in this and tlie 

 subsequent series are reduced to vacuum standards, and all weighings 

 were made against corresponding tares. 



Au. Ag^. Ratio. 



7.6075 12.4875 60.921 



8.4212 13.8280 6o.goo 



6.9407 11.3973 60.898 



3.3682 5-5286 60.923 



2.8244 4-6371 60.909 



Mean, 60.910, ± .0034 

 Hence Ag : Au : : 100 : 182.730, ± .0102. 



*Ber. Deutsch. Chera. Gesell., 20, 2365. 1SS7. 

 tBerichte, 20, 3036, and Journ. Chem. Soc, 51, 866. 1SS7. 

 X Berichte, 21, 126. 1888. 

 g Philosophical Transactions, 180, 395. 1889. 



