1852.] OF THE ROYAL INSTITUTION. 205 
WEEKLY EVENING MEETING, 
Friday, May 28. 
Wittiam Pots, Esq., M.A., F.R.S., Treasurer and Vice-President, 
in the Chair. 
Joun Percy, M.D., F.R.S., < 
LECTURER ON METALLURGY AT THE GOVERNMENT SCHOOL OF MINES, &c. 
On the Modes of Extracting Gold from its Ores. 
Dr. Percy began by stating that it was not his intention to touch 
upon any of those very interesting and important questions,— the dis- 
tribution of Gold upon the earth’s surface; the geological features 
of the regions which are believed to be indicative, not to say charac- 
teristic, of its presence; or the probable economical effect which 
the present unexampled supply may be expected to produce. To 
treat these subjects satisfactorily would require very much more 
time than that allotted to him on the present occasion. He should, 
therefore, direct special attention to certain points which he had 
reason to believe to be at the present time the most interesting. 
After a brief review of the physical and chemical properties of 
gold, of special importance in the consideration of the subject, the 
Lecture was treated as follows : — 
Modes of occurrence of Gold in nature.— Gold almost always 
occurs in nature in the metallic state; not pure, but alloyed with 
silver in various proportions and with the occasional addition of 
small quantities of iron and copper. A table* was presented, shewing 
the composition of native gold from various parts of the world. The 
presence of silver is constant with one or two rare exceptions; and 
its proportion varies not only in native gold from different auri- 
ferous districts, but even in specimens from the same locality. In 
Hungary gold is met with in combination with Tellurium. Native 
gold occurs crystallized and amorphous in small grains of greater 
or less size, in lamina, and sometimes in masses of the weight of 
many pounds. 
Matters associated with native Gold.— These are various, such as 
quartz, either massive, or in a state of fine division as siliceous 
sand,—clay,— frequently certain kinds of iron pyrites,—rarely galena, 
&c. It seems doubtful whether in every instance the gold occurring 
in association with iron pyrites is wholly in the metallic state-— Spe- 
{* The Members are referred, for many of the tables and diagrams illustrating 
this discourse, to Dr. Percy’s Lecture, forming one of “ The Lectures on Gold, 
delivered at the Museum of Practical Geology,” published by Bogue, price 2s. 6d.] 
