17 



of grains of gold per ton is found by x 3 x 0*2045288, in 

 which x=the diameter of the sphere of gold in thou- 

 sandths of an inch. By taking 978 grains for assay x 3 = 

 grains of gold per ton. 

 To test the accuracy of the above figures a comparatively 

 speaking large sphere of gold from an assay was measured, and 

 found to be 0*593 mm., or ^j of a millimetre in diameter, 

 and 59*3 3 x 0*000000102102=0*002129 of a gramme. When 

 weighed on a very delicate balance it was found to weigh 

 00021 gramme, and as this balance does not indicate beyond 

 the fourth decimal the results may be considered identical. 

 This sphere indicated gold in the sample tried at the rate of 

 3ozs. 9 dwts. 13grs. per ton. The smallest sphere of gold I 

 have yet measured was 0*024 mm. in diameter, and by applying 

 the above rule the weight would be 2*4 3 x 00000000102102 x 

 15*43235 (to convert grammes to grains) =0*000002178, or a 

 trifle over two millionths of a grain. 



Spheres of silver may be obtained and measured in a similar 

 manner ; the boracic acid acts slightly on the silver, but the 

 quantity dissolved is inappreciable, as the action is not pro- 

 longed. The specific gravity of silver being 10*53 the weight 

 of y^ mm. would be 0*0000000005236 x 10*53= 

 0*000000005513508 of a gramme. In a test assay made with 

 silver the sphere measured 0*57=yo 7 o oi a mm., from which 

 the weight deducted would be 0*00102096 of a grain, the 

 balance showing the weight as 0*0010. 



Copper, lead, and other metals cannot be melted in boracic 

 acid on platinum wire without dissolving to a perceptible 

 amount, but may with care be melted in sodic carbonate, and 

 by dissolving the latter in hot water the sphere of copper, &c.,. 

 obtained and measured. 



