15 



On the Production and Measurement of 

 Gold and other Metallic Spheres to 

 Determine their Weight. 



By Mr. Gr. G-oyder, Jim. 

 [Read July 6, 1886.] 



In making assays for gold where the amount of gold is very 

 small alittle silver is required in which the gold maybe collected. 

 As nearly all commercial litharge contains silver it is rarely 

 necessary to add any separately for this purpose. The litharge 

 I at present use contains at the rate of six pennyweights of 

 silver and one- seventh of a grain of gold per ton. 



Having obtained a prill in which the amount of gold is a 

 third, or less than the silver, the prill is boiled in dilute nitric 

 acid in a porcelain capsule, to dissolve the silver ; and where 

 the amount of gold is more than one pennyweight to the ton, a 

 second boiling in strong nitric acid should be given. If care 

 be taken in using dilute acid at first and boiling gently the gold 

 will be left in one piece of a nearly black colour. The acid is 

 now decanted off, and the gold washed two or three times with 

 distilled water. The gold may now be placed on an aluminium 

 or other polished metal plate by inverting the capsule and 

 leading the last drop of water and the gold with a glass rod 

 on to the plate ; the water is drawn off by a piece of filter 

 paper, and the plate gently heated till dry. 



Having thus obtained the gold in a pure state, a bead is 

 made with boracic acid on a platinum wire loop, and pressed on 

 the gold while still red hot. The gold adheres without diffi- 

 culty, and by heating the bead before the blowpipe the gold is 

 obtained as an almost perfect sphere. Should the resulting 

 sphere of gold be very minute it is better to measure it under 

 the microscope while in the bead, but if large enough to be 

 seen with the naked eye it can be measured more accurately 

 after dissolving the boracic acid bead in a watch glass with hot 

 water, and placing the sphere of gold on a glass slide. 



The plan of measuring minute prills of silver and gold to 

 determine their weight was first introduced by Harkort, who 

 used an ivory scale engraved with two fine lines, meeting at an 

 acute angle, and divided into fifty equal parts. According to 

 the fifth edition of Plattner's " Probirkunst," page 520, G-old- 

 schmidt determines the weight of silver and gold prills by 



