322 ALBERT D. BROKAW 



series. The substances studied were ferric sulphate, ferric chloride, 

 sulphuric acid, hydrochloric acid, and manganese dioxide. These 

 were covered by the following experiments, each in duplicate. Solu- 

 tion of gold is shown by loss of weight. 



1. Fe,(S04)3+H3S04+Au 



{a) no weighable loss. 

 (6) " 



2. Fe,(S04)3+H,S04+Mn03+Au 



(a) no weighable loss. 

 {h) .00017 g. loss.^ 



3. FeCl3+HCl+Au 



(a) no weighable loss. 

 {b) " 



4. FeCl3 + HCl+MnO,+Au 



{a) .01640 g. loss. Area of plate 383 sq. mm. 

 {h) .01502 g. " " " " 348 "^ " ^ 



The solutions were tenth normaP with respect to ferric salt and to 

 acid. In each duplicate 50 c.c. were used. In experiments 2 and 4, 

 I g. of powdered manganese dioxide was added to each duplicate. 

 The gold was obtained from Goldschmidt Bros, and assayed 99.9 

 per cent pure. It was rolled to a thickness of about .002 in., and cut 

 into pieces of about 350 sq. mm. area, and one piece, weighing about 

 o . 15 g., was used in each duplicate. The gold was washed with alco- 

 hol and ether and dried, then each piece was carefully weighed. The 

 experiments were carried on in tightly stoppered test-tubes which 

 were thoroughly shaken from time to time. After two weeks the 

 pieces of gold were removed by means of a platinum wire, and washed 

 with water, alcohol, and ether, in turn, before weighing. In experi- 

 ments 2 and 4 a small amount of manganese dioxide adhering to the 

 plates was removed by means of a solution of ferrous sulphate acidi- 

 fied with sulphuric acid, after which the plates were treated as above. 

 At the end of two weeks all but experiment 4 gave negative results 

 when weighings were made to 0.0001 g., and the balance was ex- 



1 This duplicate was found to contain a trace of CI which probably accounts for the 

 loss. 



2 Normal as used in this paper refers to "equivalent normal" solutions. Tenth 

 normal concentration was selected rather arbitrarily except for the fact that it is well 

 within the range of concentration shown by mine waters. (See table of analyses, p. 326.) 



