172 SMITHSOXIAX MISCELLANEOUS COLLECTIONS VOL. 54 



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

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

 this argument Thorpe and Laurie ' 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 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, which 

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

 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 weight of pure silver was added. 

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

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

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

 needed to precipitate the three atoms of chlorine combined with it; in 

 other words, the ratio 3Ag: Au : : 100 : r. All weights in this and the 

 subsequent series are reduced to a vacuum standard, and all weighings 

 were made against corresponding tares : 



Au. Ag. Ratio. 



7.6075 12.4875 60.921 



8.4212 13.8280 60.900 



6.9407 11.8973 60.898 



3.3682 5.5286 60.923 



2.8244 4.6371 60.909 



Mean, 60.910. ± .0034 



Hence Ag: Au :: 100 : 182.730, d=. 0102, and Au = 197.13. 



The second series of determinations was essentially like the first, ex- 

 cept that auric bromide was taken instead' of the chloride. The ratio 

 measured, 3Ag: Au, is precisely the same as before. Eesults as follows: 



Mean, 60.927, ± .0038 

 Hence Ag: Au: : 100: 182.781, ±.0114, and Au = 197.18. 



^Berichte, 20, 3036, and Journ. Chum. Soc, 51, 866. 18S7. 



^'Berichte, 21, 126. 1888. 



" Philosophical Transactions, ISO, 395. 1889. 



