ASSAYING. 129 



was therefore resorted to. After they were loosened from the bone ash, the 

 cupel was tipped up and the buttons were allowed to fall upon a polished 

 steel anvil. When struck by a polished steel hammer any adhering impuri- 

 ties were removed and the flattened button was found sticking to the face of 

 the hammer, from which it could be easily brushed into the scale-pan. 



Manner of weighing. — In the Becker balance, used in weighing the silver but- 

 tons, the right arm of the beam is divided into twenty parts. If a rider 

 weighing .005 grain is used each one of these spaces will represent .001 

 grain, and if a weight of rock equal to 377.09 grains is used in making the 

 assays each one of these parts will represent 10 cents to the ton, or 0.0002652 

 per cent. By placing a card-board scale, on which each one of these parts 

 is divided into ten, behind the beam and using a magnifying glass in front 

 of it the position of the rider between any two of the points marked on 

 the beam can be determined with accuracy up to one-tenth of the space, 

 which would represent a value of one cent to the ton (0.0000265 per cent.). 

 "When new and in good order the Becker balance is sensitive up to .0001 

 grain, which represents a value of one cent to the ton. Allowing a differ- 

 ence of one cent (0.0000265 per cent.) one way or the other, it is safe to say 

 that buttons can be weighed with almost absolute accuracy up to within 

 two cents to the ton, or plus or minus one cent. As is well known, Harkort 

 and afterward Plattner," instead of attempting to weigh extremely small but- 

 tons, measured their diameters between two fine lines converging at a small 

 angle, which were engraved on an ivory scale. Very small silver buttons are 

 almost exactly spherical, and the method is therefore not only rational but cal- 

 culated to give more exact results than weighing, but it requires very delicate 

 manipulation to place the button so that both lines are exactly tangent to it. 

 A common microscope with a micrometer eye-piece may be used instead of 

 Plattner's scale, and the measurement made both more rapidly and more 

 accurately. This method also obviates the necessity of removing the but- 

 tons from the cupel. 



inaccuracies of the results. — Admitting that the loss by cupellation is so small 

 that it can be neglected, and that the method of weighing is correct within 

 two cents, the other sources of inaccuracy attending the assaying of rock 

 containing but minute quantities of silver are reduced to two, the imperfect 



" Plattner's Probrikunst. Theodor Richter, p. 35 ; Leipzig, 1865. 

 2654 L 9 



