RONE- ASH CUPELS. 119 



To prepare Bone-ash Cupels. 



The ash of burnt bones (that of the sheep or horse is 

 preferable) should, in not too fine nor too coarse a state, be 

 mixed with water (about an ounce of water to a pound of 

 bone ash), so that it may, when of the proper consistency, 

 adhere together when pressed, although not stick to the 

 fingers. Place a metal disc a coin if it fits well into the 

 bottom of the cupel mould, and then fill the cavity with 

 bone-ash ; place the hammer with the convex base on the 

 top of the ash and give it a smart blow by a mallet or other 

 hammer. The cupel can then, by means of the finger, be 

 pushed uppermost and out of the mould. 



Assay for certain Metals other than Gold or Silver. 



To find the amount of lead in Galena, the usual lead 

 ore. 



Charge powdered ore, two or three times the weight of 

 carbonate of soda, three iron nails (tenpenny) placed in 

 the top for taking up the sulphur, and a cover of salt or 

 borax. 



The assay may be conducted in a muffle or other 

 furnace. 



The crucible two-thirds full of ore and fluxes should 

 be heated to redness, and the temperature gradually raised 

 until the operation is finished, which will be in about twenty 

 or twenty -five minutes. 



The contents of the crucible are to be poured into a 

 mould, and, when cool, the lead button separated from the 

 slag. 



Weight of button , AA , 



TI7 - . , . .. i X 100 = percentage of metal. 



Weight of ore sample 



As galena always contains more or less silver, the resulting 

 button ought to be assayed for the precious metal in the 

 cupel. As a cupel does not conveniently absorb much more 

 than its own weight of lead, the button may have to be 

 divided into two or more portions, and each of these 

 cupelled separately. 



Galena may be roughly assayed for lead by placing the 

 powdered ore, without fluxes, in an iron dish, and exposing 

 ii to the heat of a blacksmith's forge. 



