90 On "Surcharge" of the Bullion Assay. 



approximately corresponding to the presumed fineness of 

 the several assay pieces under trial, correcting each of the 

 latter by its corresponding proof; gold of '9 by the 9 grains 

 proof, gold of '7 by the 7 grains proof, and so on (supposing 

 the assay pound in these instances to be 10 grains). But 

 with rough gold especially, of which often a large range of 

 finenesses is passed in one fire, it would be exceedingly 

 operose to provide proofs for each variation and for com- 

 mercial, as distinguished from purely experimental work, 

 some kind of general rule or compromise has to be made. 

 The following experimental trials illustrate the case : 



Silver employed 2J times the weight of the gold. 



Lead ,, 84 grains. 



All other conditions the same throughout. 



According to the above results, when with full pound of 



fine gold, the surcharge equals + '00085. Then, 



With 8 grains under same influences the surcharge is reduced to one-half. 

 With 7 „ ,, „ ,, to one-quarter. 



At 6 ,, ,, ,, ,, to zero. 



At 2-5 the " minusage " is nearly equal in amount to the " plusage " at 10. 



Of course by altering the weight of lead or in any other 

 manner modifying the ruling conditions, other figures would 

 be obtained, but special experiment under any given routine 

 would show the interrelation existing between the surcharge 

 quantities for the several finenesses of gold. 



The attached graphic illustration shows the results of 

 these experiments. The vertical column represents sur- 

 charge ; the horizontal series of figures shows fineness or 



quantity of gold contained in the assay ; the line A ( ) 



connects the results of actual experiments ; the line 



_g ( ) averages the results ; and the straight line 



C ( ) connects the extreme results. 



When samples of gold of different finenesses are passed 

 with proofs of the full pound of fine gold, with proportions 

 of silver and lead, &c, as already stated ; from the surcharge 

 indicated by these proofs, that for any low gold may be 

 approximately estimated by reference to the subjoined table 

 deduced from lines ruled parallel to G, 



Half these experiments were performed by Mr. Foord, and 

 half by myself, so that personal error may be considered to 

 be eliminated by the combination of results. 



