62 Assaying Ores of the Precious Metals. 



combines with the lead, and multitudes of little scales of 

 litharge form upon the surface of the glowing metal. Dart- 

 ing from its centre outward, they fall upon the cupel at the 

 circumference of the button where they disappear alto- 

 gether, being quickly absorbed by the porous bone ash. 

 In this way the lead is gradually carried into the substance 

 of the cupel while every particle of precious metal is left 

 behind. At length the little button suddenly displays a 

 surface over which play all the beautiful colors of the rain- 

 bow. This splendid appearance continues until, the su- 

 preme moment having arrived when the last trace of baser 

 material has been driven away, the little button of precious 

 metal, with dazzling brightness, remains unmoved in the 

 intense heat of the furnace. It is then taken from the fire 

 and carefully cooled, after which it only remains for the 

 assayerto consult his balance to learn the value of the ore. 



The blow-pipe is a favorite instrument when the mere 

 presence of precious metal is to be determined. The small 

 amount of necessary apparatus to accompany it and the 

 simplicity of the operations required, highly commend it 

 and have prompted many attempts to extend its application 

 to the quantitative estimation of these metals. Methods 

 have been devised by Plattner and others, which, in the 

 hands of skillful operators do, doubtless, give satisfactory 

 results, but they have never become popular with assayists. 

 The objection to these methods does not spring from want 

 of confidence in the chemical actions involved ; these are 

 satisfactory : nor from the amount of labor required, for 

 this is less than the furnace demands. The objection to 

 the use of the blow-pipe for determining the value of 

 ores, springs from the necessity of using such small quanti- 

 ties of ore that the silver button obtained from it is too 

 minute to be satisfactorily valued. Rarely can this button 

 be obtained large enough to be weighed. Its value is gener- 

 ally sought by measuring its diameter and comparing it 



