SILVER COI^^S. 399 



SaU. Hence, to find the quantity of silver in muriate of 

 silver dried at a heat of nearl}^ 400", we have only to mul- 

 tiply its weight by 0.756. This was the method which I 

 followed. It corresponds very nearly with the result of former 

 anslyses as rtiade by others. 



4. Tiie solution thus freed from the silver, and containing a Kesidvie of the 

 considerable excess of muriate of soda, vvas mixed with fill the ^^^^^^"^ j^_ " 

 water employed to wash the muriate of silver, and evaporated dissolved. 

 to dryness in a porcelain capsule. The dry mass was dissolved 

 in water. Sometimes alittle muriate of silver separated during 

 the solution. It was always carefully washed, and added to 

 the precipitate of silver previously obtained. 



' A polished plate of iron was then put into the liquid, which Precipitatioti 

 was diluted with water, if necessary, till it just covered the j^ ji-oii^^^" 

 upper end of the plate ; it was then laid aside till the whole of 

 the ctDpper was thrown down. Two days were usually required 

 for this separation; sometimes longer, sometimes a shorter 

 time sufficed. Care was taken not to disturb the liquid during 

 the process; for when the copper falls down, the separation is 

 always more tedious. When the process was finished, the plate 

 of iron was withdrawn, and the copper washed from it in dis- 

 tilled water. A portion of the copper often fell down when the 

 plate was withdrawn. As soon as it had subsided, the liquor 

 was decanted off, and water, acidulated with muriatic acid, 

 poured upon the copper. This also was poured off after a few 

 minutes, »nd pure water substituted in its place. The portion 

 of copper washed oif the iron plate was edulcorated in the 

 same manner with water acidulated with- muriatic acid. The 

 whole was then collected on a fdter, and carefully washed. 

 It was allowed to dry in the open air, and aftervv'ards placed 

 f()r some hours on a steam bath. It was then weighed, and 

 considered as the proportion of copper contained in the coiii. 



As copper in the metallic stale does not combine with water. Desiccation o: 

 the powder thus obtained is easily dried. Indeed, if it be tho- ^^^ copper, 

 roughly dried in the open air, it loses no sensible weight after- 

 wards, though heated to 300". It cannot be heated to red- 

 ness, because even though this be done in a covered crucible, 

 it very rapidly combines with oxygen, and is converted into a 

 black powder. If it be heated to redness in an open crucible, 

 100 grains generally increase in weight to 120 grains. 



Almost 



