Intelligence and Miscellaneous Articles. 425 



still a gap, from the 22nd of September to the 7th of October 

 to fill up; as soon as that is done, 1 will immediately proceed to a 

 complete comparison of all observations, and think that I shall be 

 ready with it in eight or ten days; and I then hope to be able to 

 send you a more full and detailed communication. 

 Halle, Oct. 13, 1835. A - Rosbnbbbobb. 



(Sent as a circular by Prof. Schumacher from Altona, Oct. 17, 1835.) 





OBSERVATIONS ON THE ASSAY OF SILVER IN THE HUMID WAY. 

 BY M. GAY LUSSAC. 



There was lately sent to the Assay Office in Paris an ingot of 

 silver, containing 3-1000dths of gold, which had been stated by one 

 assayer to contain 990, and by another 995 thousandths of silver. 

 Numerous assays made by M. Besseyre, to whom M. Gay Lussac 

 had confided the process, gave 996J thousandths of silver in the 

 ingot; this proportion, added to the 3-1000dth of gold, gave 999| 

 as the sum of the precious metals. This result excited our attention, 

 for we had never found the fine silver of commerce so pure as to ex- 

 ceed 997 to 998 thousandths. On the other hand, the cupellation to 

 which the ingot was subjected to determine the quantity of gold 

 which it contained, gave only 990 thousandths of silver, instead of 

 996^ found by the humid way. These results agree with those ob- 

 tained by the commercial assayers, one of whom had operated in the 

 humid way and the other by cupellation. 



Surprised at so great a difference, M. Gay Lussac made researches 

 as to its cause, and he found that it was owing to mercury contained 

 in the ingot. On adding five milligrammes of mercury and one gramme 

 of pure silver, he found, after dissolving the silver in nitric acid and 

 precipitating it by common salt, that the silver had increased about 

 four thousandths. Instructed by this synthetic experiment, he ex- 

 posed 50 grammes of the ingot, in a small porcelain retort, to a very 

 high temperature, and he obtained small globules of mercury visible 

 to the naked eye. 



The cause of the different fineness obtained by the two processes 

 being thus known, it remained to correct it, in order to give the humid 

 process that degree of certainty which it appeared to have lost by this 

 unexpected circumstance; for although silver containing mercury is 

 very rare in commerce, it is sufficient that the case has happened to 

 put the assayer on his guard, and supply him with the means of over- 

 coming it. 



M. Gay Lussac at first thought that the mercury had not been 

 completely oxidated, and that it would then precipitate with the sil- 

 ver as an insoluble chloride; but an assay of pure silver to which six 

 thousandths of completely oxidated mercury were added in nitric acid 

 gave 1005 thousandths, instead of 1000 as ought to have been ob- 

 tained : this result proves that the mercury was precipitated with the 

 silver. 



It was then supposed that the mercury, although at the maximum 

 of oxidation, might have been reduced to the minimum, at the mo- 

 Third Series. Vol. 7. No. 41. Nov. 1835. 3 1 



