Page 219 - My FlipBook

GOLD. — — — 207 ;

"To illustrate this, take the following" cxaini)le :
"
Raise i pennyweight of i6-carat gold to 18 carats.
"The numbers representing the proportions of alloy in
this exam])le are found by respectively subtracting" 18 and
16 from 24. The statement is, therefore
6:8:: i: iVs.
from which it follows that to raise i pennyweight of 16
carat gold to 18 carats, there must be one-third of a penny-
weight of pure gold added to it.
" But suppose that, instead of pure gold, w^e w^ish to effect
the change by adding 22-carat gold. The numbers, then,
respectively representing the proportions of the alloy would
be found by subtracting, in the above example, 16 and 18
from 22, and the statement would be

4:6 : : I : iH.
" It follow^s, then, that to each pennyweight of i6-carat
gold a half pennyweight of 22-carat gold must be added
to bring it to 18 carats."

CONVERTING GOLD ALLOYS INTO THE REQUIRED FORMS
FOR DENTAL PURPOSES.
Procuring an Ingot.—The metal to be molded in the
form of ingot is put into a clean crucible lined on the inside
with borax, and placed in the furnace. As soon as the
metals are fused, the crucible should be removed and the
contents poured cjuickly but carefully into the ingot-molds
the latter being conveniently near the furnace, as the molten
metals soon become chilled on exposure to the open air.
Before pouring, the molds, if made of iron, should be mod-
erately heated and oiled, or coated with lamp smoke by
holding their inner surfaces over the fiame of an oil lamp
or gas-jet.