4 
Transactions of the Society. 
and such steel withstood the test to which it was submitted. This 
does not prove that 0*05 p.c. phosphorus is too low a maximum, 
but rather that a fairly large margin of safety is allowed. 
In the case of cast iron, which is usually made from a mixture 
of pig irons, much higher percentages may be allowed, and in some 
cases, especially where thin castings and those of intricate design 
are required, the phosphorus content may reach 2 p.c., but as in 
the case of steel, increased phosphorus results in increased brittle- 
ness. It is not difficult to microscopically detect the presence of 
phosphorus in cast iron, particularly after the polished specimen 
has been heat-tinted, as the phosphorus compound (probably Fe 3 P) 
forms a characteristic eutectic with iron. This is shown in fig. 1, 
taken at a magnification of 1000 diameters from a piece of cast 
iron containing 0 ■ 85 p.c. phosphorus. 
Small quantities of bismuth or antimony in copper or brass 
exert an injurious effect by separating as constituents to the 
crystal boundaries and forming thin brittle walls. 
Turning now to the existence of small quantities of metals 
which do not necessarily exert an injurious effect, the presence of 
the platinum metals in silver and gold maybe cited as an example. 
The importance of being able to detect easily the platinum 
metals, especially during the assay for gold and silver, will be 
gathered from the increased demand and the high price of these 
metals. The following table gives the average price of platinum 
per troy ounce in New York for the years 19il to 1919 inclusive : — 
Per Troy Oz. 
At $5 to the 
$ 
£ 
s. 
d. 
1911 
43.12 
8 
12 
6 
1912 
45.55 
9 
2 
3 
1913 
44.88 
8 
19 
6 
1914 
45.14 
9 
0 
7 
1915 
47.13 
9 
8 
6 
1916 
83.40 
16 
13 
8 
1917 
102.82 
20 
11 
5 
1918 
105.95 
21 
3 10 
1919 
114.61 
22 
18 
6 
Gold and silver assays are almost invariably carried out by the 
dry method, in which gold, silver, platinum, etc., are alloyed with 
metallic lead and then recovered by cupellation. In cupellation 
advantage is taken of the fact that the precious metals do not 
form oxides when heated in the air, whereas lead forms lead oxide 
which at the temperature of cupellation is sufficiently liquid to 
allow of it being absorbed by the bed or cupel on which the opera- 
tion is carried out. 
