576 



ON SILVER. 



yields 10 per cent by fusion will not give above 8|, 9, ot 

 thereabouts, by precipitation. Th« estimation deduced 

 from the muriat of silver too being a language not un- 

 derstood by those, who would have the clear product of 

 their ores set before their eyes, it is better to proceed to 

 the assay by fusion. The following method, an imitation 

 of the operation in the large way, and practised by Sage, 

 appears to me preferable to any other. 

 The best me- Melt a quintal of the roasted ore with as much litharge, 

 t'^'^db ^ S '^^^' ^"^ ^^'''ce quintals of common carbonat of potash, in a 

 crucible, the bottom of which is lined with 24 or 30 

 grains of charcoal, softened with a little oil, so that the 

 paste may be applied to the bottom and half way up the 

 side by the finger. Put on a cover, but without luting it. 

 Place two such crucibles side by side in a common fur- 

 nace, and cover them with charcoal. The bellows are 

 not necessary. When the mixtures enter into fusion, 

 which will readily be perceived by the ear, push the 

 charcoal aside, so that you may be able to take off the 

 lids, and see what is going on. If the efiervescence raise 

 the contents above the middle of the crucible, remove the ^ 

 lids, when the weight of the air will check the swell, and 

 prevent it from running over. As soon as all is quiet, 

 put on the lids again, cover up the crucibles with char- 

 coal, and let them ^tand till they are cold. If the assd,ys 

 have been well fused, the leads obtained will not differ in 

 weight two grains. Subject them to cupellation, and you 

 will obtain buttons, which ought not to differ a sixteenth ^ 

 of a grain. A sixteenth of a grain represents an ounce 

 in a hundred pounds : but if the ore be so poor as to yield 

 less than an ounce, as is the case with most of the mines 

 at present worked in America, the assay should be made 

 with four hundred grains at least. 



Niirat of Silver at a Minimum, 

 Trcparation of In a solution already saturated boil powder of silver, 



nnimmum ni- ^^^^ ^^^ instance as is obtained in ordinary parting ; and 

 - liAb oi Silver* ■ 1 *» 



> continue the ebullition for an hour after nitrous gas has 



ceased to be evolved. Pour off the liquid with its sedi- 

 ment, and leave it to grow clear by subsidence. I>raw 

 off the clear fluid with a bulbed siphon, and, if you wish 



to 



