SCIENCE. 
119 
THE REDUCTION OF CHLORIDE ORES. 
For the benefit of those not familiar with the processes of 
reducing gold and silver ores, a brief explanation of what 
is meant by “free milling,” an expression so often used by 
mining men, may not be out of place. In separating, by 
amalgamation, the precious metals from gangue or waste 
rock with which they are almost always associated, it is 
necessary to the success of the process to present the parti- 
cles of gold or silver contained in the ore to the mercury 
with which they are to be alloyed, in such form that the 
latter can seize upon them readily. If these metals always 
occurred in nature in their pure metallic state, this would 
be a very easy matter. In free milling gold ores it is fre- 
quently only necessary to place the quicksilver beneath the 
stamps of the battery in which the ore is crushed, and upon 
an inclined copper plate over which the pulp is carried by 
water after it leaves the battery. The stamps, by reducing 
the rock to fine particles, release the minute scales and 
crystals of gold, which are readily taken up by the quick- 
silver, while the rock, for which the mercury has no affinity, 
is carried away as “ tailings.” 
But silver rarely occurs in a native or pure metallic state. 
It is usually mixed with clorine, lead, iron, sulphur, man- 
ganese, copper, antimony and other base metals, and is 
found in the form of chloride of silver, argentiferous galena, 
in which the silver is in the form of a sulphide, and in 
many other compounds, for most of which quicksilver has 
no more affinity than it has for the common rock of the gan- 
gue. In most cases, therefore, if the silver ore was simply 
crushed and brought into contact with an amalgamating 
surface, little or none of the metal would be caught by the 
quicksilver and saved. Mercury has a strong affinity for 
metallic silver, stronger even than that of chloride, so that 
ff chloride of silver and quicksilver are brought together 
the mercury will seize the silver, forming an amalgam, and 
the chlorine which is released will escape as gas or unite 
with some other substance which presents itself and for 
which it has an affinity ; but sulphur will not give up sil- 
ver, with which it is chemically mixed, to mercury, unless 
the sulphur has first been driven off by fire. This process 
of converting chloride o( silver into an amalgam is not an 
instantaneous one like the amalgamation of free gold, 
but requires several hours to be perfected, and it is 
hastened by the presence of other chemicals, such as sul- 
phate of copper, sulphuric acid, and cyanide of potassium, 
the action of which it is unnecessary to explain here. 
In order to reduce silver ores by amalgamation, it is 
necessary, as will be understood from the above explana- 
tion, to have the particles of metal either in a pure or 
chloritic state. When they are found in nature in either of 
these conditions they need no special treatment before being 
put into the mill, and the treatment of them is called ‘■‘raw 
amalgamation.” The process employed is to crush the ore 
to a fine pulp, and then transfer it to a large round iron tub, 
where it is agitated for several hours in hot water with 
quicksilver, some or all the chemicals I have named being 
added with common salt to promote the union of the mer- 
cury and the silver. If the silver in the ore is in the form 
of a sulphide, as it frequently is, and the amalgamation pro- 
cess of reduction is to be employed, the ores have to be 
roasted with common salt for several hours after they are 
crushed. Without explaining in full the chemical reactions, 
I may simply say that the heat volatilizes the sulphur mixed 
with the silver, and separates the salt into its constituents 
of chlorine and sodium, the first of which unites with the 
silver from which the sulphur has been driven off, and forms 
a chloride which is then ready for the amalgamating pan. 
The desulphurization and chlorination of an ore is an ex- 
pensive process, and greatly increases the cost of reduction. 
When such metals as lead, zinc, or copper are present in 
ores in large quantities, it is usually cheaper to reduce them 
by smelting, and by that process the lead and copper are 
generally saved and add to the value of the product. 
Almost any ore can be reduced by fire, if it is mixed in 
small proportions with ether smelting ores. In large smelt- 
ing establishments like those at Denver, Omaha, and 
Newark, N. J., where great varieties of ores are purchased, 
even free milling rock can be used to advantage ; but the 
reduction of most free milling ores by fire, without mixture 
with others, would be ruinously expensive if not physically 
mpracticable. 
ON CURRENTS PRODUCED BY FRICTION BE- 
TWEEN CONDUCTING SUBSTANCES AND ON 
A NEW FORM OF TELEPHONE RECEIVER* 
In a communication to the Royal Society of Edinburgh 
of date January 6, 1879, I showed that “electric currents 
were produced by the mere friction between conducting 
substances.” The existence of these currents can be easily 
demonstrated either by a telephone or a Thomson’s galvano- 
meter. I have since found that these currents are, for all 
pairs of metals which I have yet tried, in the same direction 
as the thermo-electric current got by heating the junction 
of the same two metals. They are also approximately at 
least, stronger in proportion as the metals rubbed are far 
apart on the thermo-electric scale — the strongest current, as 
far as I have yet observed, being got by rubbing antimony 
and bismuth together. These observations clearly point to 
a thermo-electric origin for the currents ; but it is possible 
that they may be due partly to the currents suggested by 
Sir William Thomson as the cause of friction, and partly, 
also, to contact force between films of air or oxide adhering 
to the surfaces of the metals. 
Having ascertained that these friction-currents are of 
some strength and fairly constant, I proceeded to make 
several kinds of machines for producing currents on this 
principle. One of them consists of a cylinder of antimony, 
which can be rotated rapidly, while a plate of bismuth is 
pressed hard against it by a stiff spring. When this ma- 
chine is included in the same circuit with a microphone and 
a Bell telephone, the current got from it is quite sufficient 
to serve for the transmission of musical sounds and also 
loud speaking. The transmitter, which I have found most 
serviceable in my experiments, is made by screwing two 
small cubes of gas-carbon to a violin, and placing between 
them a long stick of carbon pointed at both ends, the points 
being made to rest in conical holes in the carbon cubes. 
The looseness of the contact is regulated by a paper spring. 
This forms an excellent and handy transmitter for all kinds 
of musical sounds, and also serves very well for transmit- 
ting speech. 
Seeing that friction between metals clearly produces a 
current, it seemed natural to inquire if the converse held 
good, that is, if a current from a battery sent across the 
junction of two metals affected the friction of the one upon 
the other. I have tested for this in a variety of ways, and 
the results obtained leave me in doubt whether to attribute 
them to variations in the friction, or to actual sticking por- 
duced by fusion of the points of contact through which the 
current passes. The most noticable effect is produced when 
one of the rubbing bodies is a mere point, and the other a 
smooth surface of metal. This led me to make a modifica- 
tion of the loud speaking telephone of Mr. Edison, in 
order to get audible indications of changes of friction pro- 
duced by the passing of a variable current. It consists of 
a cylinder of bismuth accurately turned and revolving on 
centres. The rubber-point is made of a sewing-needle with 
its point bent at right angles, and its other end attached to 
the centre of the mica disk of a phonograph mouthpiece. 
It is evident that this is only a loose contact, which can be 
perpetually changed. When this apparatus is included in 
the circuit with the violin-microphone and three or four 
Bunsen cells, the violin sounds, as was to be expected, are 
heard proceeding from the loose contact, even when the 
cylinder is not rotated. They are increased, however, in a 
remarkable degree by rotating the cylinder slowly, so much 
so that a tune played on the violin can, with proper care, 
be distinctly heard all over an ordinary room. 
With regard to the explanation of this effect, it is evident 
that electrolysis can in no sense come into play, as is sup- 
posed to be the case in Edison’s instrument. I am inclined 
to look for the explanation rather in the direction of the 
Trevelyan rocker, although the circumstances are consid- 
erably different in the two cases. In the rocker we have the 
heat passing from a mass of hot metal through two points 
of support to a cold block, whereas, in the other case, the 
heat is only intense at the points of contact, the rest of the 
metals being comparatively unaffected. The variations n 
the current produced by the transmitting microphone must 
* Abstract of a paper read before the Royal Society of Edinburgh by 
James Blyth, M. A., F.R.S.E.,on May 3. 1880. 
