11.1?11.1?11.1
The calculations are simplified by the use of a table of cubes. The
standard prills used in the comparison should not differ much in size
from the prills to be determined. They are prepared by alloying known
weights of gold and lead, so as to get an alloy of known composition,
say one per cent. gold. Portions of the alloy containing the weight of
gold required (say 0.1 milligram) are then weighed off and cupelled on
small smooth cupels, made with the finest bone-ash. Care must be taken
to remove the cupels as soon as cupellation has finished. Several
standard prills of the same size should be made at the same time, and
their mean diameter calculated. The lead for making the gold-lead alloy
is prepared from litharge purified by reducing from it about 10 per
cent. of its lead by fusion with a suitable proportion of flour; the
purified litharge is powdered, mixed with sufficient flour and reduced
to metal.
In determining the gold contained in small buttons of silver-gold alloy
obtained in assaying (and in which the silver is almost sure to be in
excess of that required for parting), transfer the button from the cupel
to a small clean porcelain crucible; pour on it a drop or two of nitric
acid (diluted with half its bulk of water), and heat gently and
cautiously until action has ceased.
Pages:
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802