I4 H. C. COOKE 
been due to the presence of a soluble impurity in the natural miner- 
als; or perhaps the artificial materials may actually dissolve less 
readily than the natural. The results obtained from Series 1 
are, however, fairly well substantiated, and the additional conclu- 
sion might be drawn that, in the case of the double compounds of 
silver with antimony or arsenic, it is the silver which is the less 
soluble constituent. This result is inferred from observation of 
pyrargyrite during the reaction; it turned black within a very few 
days, an effect which could be due only to accumulation of silver 
sulphide on its surface as antimony was leached out. The writer 
did not confirm this conclusion by analysis, however. 
EFFECT OF NATURAL REAGENTS ON METALLIC SILVER 
In the investigation of the effects that the substances in solu- 
tion in natural waters might have upon metallic silver, the reagents 
used were sodium chloride solution, hydrochloric acid solution acidi- 
fied with sulphuric acid, in the presence of manganese dioxide so 
as to insure the presence of nascent chlorine, sulphuric acid solu- 
tion, and ferric sulphate solution. The silver used was chemically 
pure leaf silver, cut into pieces about 2 sq. cm. in area, 
freed from all tarnish by scraping with a dull knife, and weighed 
to 0.00001 gm. on an assay balance. ‘These were placed in large 
test tubes, covered with 75 c.c. of solution in each case, tightly 
corked, and placed in the dark for 73 days at room temperature 
(22° C.). At the close of the time mentioned they were taken out, 
carefully washed and dried, and weighed. In the cases where the - — 
silver had been covered with a coating of chloride, this was removed 
before weighing by washing with ammonia. 
Solution Loss of Weight of Silver 
IN/TosNa@l 5.0). eel iat Mie Wo cis Aue) a ana are eee a ©.00000 gm. 
INi/to! Na @lNy//ito EL.S@}s arin Ofna eee .01538 
IN to! BIC I i ines eed 0 aie iS ae .04502 
INS/ DOSER ES Ok Sy MMe ace Ce Rar ke he eR ee OS ea . OOO1Q 
Ver es Bedy de easton a CeG. rb ne rarer ere el ialityic: Ala t |) .08252 
These experiments show clearly the powerful solvent effect 
exerted by ferric solutions on native silver. It is probably this 
reagent which leaches the silver from the outer zones of gold 
