158 R. N. Maxson — lodometric Determination of Gold. 



amount to an error of 0*00006 grm. of gold : while the arseni- 



ous acid employed in three determinations was so strong (— i 



that an inaccuracy in reading to the extent of O'Ol^""^ would 

 introduce an error of 0-0003 grm., actually greater than the 

 whole amount of gold involved in each of the individual deter- 

 minations of the greater part of the entire series of Gooch and 

 Morley, and nearly six times greater than their minimum 

 amounts. It is plain, therefore, that Rapp's experiments do 

 not relate to the small amounts of gold handled by Gooch and 

 Morley, and that experiments made with such solutions as 

 Rupp employed cannot form a basis upon which to found a 

 method for the determination of the very small amounts of 

 gold determined by Gooch and Morley. 



It has seemed to be desirable, therefore, to submit the pro- 

 cess of Kupp to further investigation. In these experiments 

 the procedure of Rupp was followed in general, but the 

 reagents were all used in solutions reasonably dilute, as must 

 be the case if accuracy is to be attained. The gold solution 

 used was prepared from pure gold chloride, and was carefully 

 standardized by means of metallic magnesium, and electroly- 

 tically with the revolving cathode, according to the method of 

 Gooch and Med way." The solution contained 0*0580^ of 

 metal in 1 liter, and was free from nitric acid. The arsenic 



N 

 solution was and was made by properly diluting a standard 



solution of — arsenious oxide. The iodine solution used was 

 approximately — , and was made by properly diluting an 



iodine solution, which had been carefully standardized against 



N 

 the — arsenic solution mentioned above. 

 10 



In reducing and determining the gold the procedure was as 

 follows:— A measured quantity of the slightly acid solution of 

 standard auric chloride was drawn from a burette into a 100^°^' 

 graduated ilask and to this was added a measured excess of a 

 standard solution of arsenious acid dissolved, as usual, in acid 

 potassium carbonate. In every case the excess of the arsenious 

 acid was considerable and the acid carbonate introduced simul- 

 taneously was enough to more than neutralize the slight 

 acidity of the auric chloride. Rupp states that the reduction 

 takes place in acid solution, but I have been unable to effect 

 the precipitation of the gold when free acid is present, but from 

 a solution made so acid that the carbonate present in the 

 * Tliis Journal, xv, 320 (1903). 



