422 
MR. F. OSMOND AND PROFESSOR ROBERTS-AUSTEN 
zinc, copper, lead, silver, &c., are attacked by certain acids which do not attack the 
gold itself.* This fact led us to hope that the use of suitable reagents would afford 
useful data. Pure nitric acid (spec. grav. 1'33) was without action in the case of twelve 
of the specimens which were subjected to its action for five minutes at a temperature 
close to its boiling point, but it developed, on the section of the alloy with indium, a 
network of either dotted or continuous lines, to which we shall again refer after we 
have described the results of a general attack by aqua regia. This observation 
confirms the indications afforded by polishing, and puts beyond question the 
existence of a cement in the alloy of gold with indium, and this alloy has not been 
submitted to the action of other reagents which attack it partially (see photo. 18). 
If the alloys were kept boiling in pure hydrochloric acid for five minutes, no result 
was produced. In a preliminary trial, where the specimens had not been previously 
perfectly cleaned, the rouge adhering to their surfaces was converted into ferric 
chloride, and all the sections were slightly tarnished. When these conditions 
prevailed only the alloy of potassium showed a black polygonal network in intaglio. 
Sulphuric acid (spec. grav. 1'84) is supposed to be without action upon gold. 
On heating our alloys, however, for five minutes, followed by a treatment for ten 
minutes, at a temperature at which white fumes were evolved (200-250°), the acid 
became tinted and the specimens were slightly attacked.! Their polish was, never¬ 
theless not materially diminished, but the greater part of them showed a network of 
fine lines of nearly uniform width, and without special coloration (see Plate 10, 
photo. 16). 
As these lines presented exactly the same characters in pure gold and in the alloys, 
it is evident that they do not afford an indication of the presence of a cement. They 
are joints of contiguous grains. But we will examine this question of joints later in 
detail. For the moment we would only note the following exception. In the case of 
the alloy with potassium, instead of a network of sunk joints, the network seemed to 
be in slight relief corresponding to that which had already been revealed by the 
action of impure hydrochloric acid. We have, therefore, three indications which 
taken separately are slender ; but they are concordant, and point to the probability of 
the existence of a cement in the alloy in question. 
General Attach by Reagents .—The polished surfaces were immersed three times 
in aqua regia (half hydrochloric, half nitric acid), the temperature being a little 
below boiling point, until effervescence began, that is to say, after about seven seconds 
each time.| Micrographic examination afforded the following results :— 
* ‘ L’or,’ par Cdmenge et Fuchs; Paris, Dunod, pp. 96-102; ‘ Encyclopedic cliimique de Fremy.’ 
H. Louis, ‘ Trans, of the Amer. Inst, of Min. Engineers,’ vol. 24, p. 705 (1894). 
f The absence of nitrons derivatives was verified by testing by ferrous sulphate. 
X Other attempts have been made to attack the alloys attached to the positive pole of a weak battery, 
by a dilute solution of cyanide of potassium (3'5 of the solid salt in 100 of water), but this reagent 
taught nothing more than aqua regia and was abandoned. 
