B 430996
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ARTES
LIBRARY
1837
SCIENTIA
VERITAS
OF THE
UNIVERSITY OF MICHIGAN !
E FLURIBUS-UNUM
TUZBU
SQUACRIS PENINSULAM AMOENAM
CIRCUMSPICE
ПИЦИНИ
TN
0.02.
K95
A TREATISE
AR!
ON

CONCENTRATION
OF ALL KINDS OF ORES:
INCLUDING THE
CHLORINATION PROCESS
FOR GOLD-BEARING SULPHURETS, ARSENIURETS,
AND GOLD AND SILVER ORES GENERALLY.
BY GUIDO KUSTEL,
MINING
ENGINEER AND
METALLURGIST,
Author of "Nevada and California Processes of Silver and Gold Extraction."
With 120 Diagrams on 7 Plates.
SAN FRANCISCO:
OFFICE OF THE MINING AND SCIENTIFIC PRESS,
No. 505 Clay Street, corner of Sansome.
1868.
Entered according to Act of Congress, in the year 1867,
By GUIDO KUSTEL,
In the Clerk's Office of the District Court of the United States for
the Northern District of California.
Printed by TRUESDELL, DEWEY & CO..
MINING AND SCIENTIFIC PRESS BOOK AND JOB OFFICE,
No. 505 Clay Street, San Francisco.
06-30-3 6 Mär
PREFACE.
This work is designed to show the present condition of the art of
concentration; putting forth the principles on which it is founded,
without entering into scientific considerations. To make the work
complete as far as possible, the processes of Dry Dressing are also
briefly described therein; and the whole is so arranged, and illustrated
by diagrams, as to enable every one to be successful in concentrating
ores. As the method of reduction by stamping is considered import-
ant, the erection and treatmeut of stamp-works, as also the construction
of grinders, are treated in full, and explained by numerous drawings.
Among the concentrating machines, the preference has been given to
self-discharging continuous contrivances; and of these again to such
as have been sufficiently investigated as to their efficiency, the amount
of water and of power required to run them, their proportion of loss,
etc. ;—circumstances entirely neglected with California inventions,—the
relative data of the latter being mere guess-work, and unreliable. A
short description of many less important contrivances may appear
superfluous, but the knowledge of them may prevent many persons
from spending time and money, as has often happened, on inventions
supposed by them to be new.
The description of Jigging Concentration, important to Eastern lead
mines, is furnished with diagrams of new continuous machines.
In addition to the strictly original matter contained in the book, facts
and rules, running through its pages, are derived from the well-known
valuable work (not yet finished,) by Professer Gætzschmann,* and
from the very complete work on Concentration by Rittinger,† which,
*Die Aufbereitung von M. E. Gætzschmann, Bergrath und Professor in Frei-
berg, 1860-1865.
†Lehrbuch der Aufbereitungs-Kunde in ihrer neuesten Entwicklung von Ritter
von Rittinger, K. K. Ministerial Rath in Wien, 1867.
4
PREFACE.
although strictly scientific in its character, describes also all the practi-
cal advance which has been made upon the subject.
The author also takes pleasure in mentioning his indebtedness to the
proprietors of the Union and Miners' Foundries, in San Francisco, for
their kind offer of the use of their exceedingly numerous collection of
patterns and drawings.
The treatise on the Chlorination of Gold and Silver ores is a strictly
chemical one, and has no connection with that on the Dressing of Ores.
It has, however, been written and published as the concluding portion
of this work, in consequence of the general demand for information on
the subject, and the great interest at present shown in respect to aurif-
erous sulphurets; the extraction of the gold therefrom being difficult
and unsatisfactory by many other processes.
SAN FRANCISCo, January, 1868.
G. KUSTEL.
CONTENTS.
·
I. INTRODUCTION.
1. The Dressing.
Dressing of Ores...
Principles of Dressing.
Division of Dressing.
•
2. The Separation.
Page.
Page
The Sluice
33
9
The Kiln..
34
12
The Step-Sluice
34
· •
20
Movable Machines.
36
The Hand Riddle.
36
The Rocker....
36
Separation of Gangue from Orc in
The Circular Hand Riddle..
37
the Mine....
24
Swinging and Jarring Riddles.
37
Dressing of Ores outside the Mine.
26
The Jarring Riddle
38
Separation by Hammers.
26
The Ragging.
26
4. Rotary Sizers.
The Spalling.
27
The Trommel or Drum..
41
The Cobbing
28
The Cylindric Trommel
42
L
Separation by Hand..
31
•
•
The Picking
31
The Prismatic Trommel
The Conical Trommel
44
•
•
46
►
The Combined Trommel.
47
U • ▸
3. Cleansing and Sizing Contrivances.
The Sifting Wheel…….
48
Washing and Sizing
•
Stationary Apparatus
33
Sizes of Grains for Jigging
50
33
II. REDUCTION.
1. Reduction of Ores.
The Mortar Blocks..
Reduction of Ores to a Proper Size
53
The Frames
Breaking under Heavy Stamps.
55
The Iron Frames.
Reduction by Rock-Breakers
56
Howland's Rotary Battery
•
Hanscom's Crusher.
57
The Straight Iron Battery
· •
Blake's Quartz Breaker.
58
Bryant's Battery.
Reduction by Stamps.
60
Wright's Iron Battery
•
2. Description of Batteries.
3. Details of a Battery.
The Foundation...
61
The Mortar.
62
63
2 8 I I I SE
64
64
64
65
65
66
6
CONTENTS.
Page.
Page.
The Stem or Lifter.
69
Remarks
103
The Shoe or Pestle..
69
The Socket or Head
The Tappet....
The California Tappet
70
8. Grinding.
72
The Arastra or Tehama
105
73
The Edge or Chili Mill.
. 107
- *
The Cams..
75
Ball Mills.
108
•
Wooden Cams
76
Lundgren's Pulverizer
109
Iron Cams
77
Cylinder Mills....
110
Farrand Mill ..
110
4. Speed, Curve and Order of Lifts.
Hopkins' Grinder
111
Limit of Speed in Crushing...
Construction of the Cam Curve...
Order of Successive Stamp Lifts..
77
Horizontal Mills..
111
78
Iron Pan Grinders.
113
•
80
Hanging-up of Stamps....
9. Pans with Plane Mullers.
83
5. The Discharge of Batteries.
The Common Pan Grinders.
The Tub Grinder
114
+
•
•
115
The Discharge in Dry-Crushing..
Bartolo's Grinder
115
84
With Grates
Without Grates
•
Knox's Pan.
115
84
·
· • ·
•
·
85
Varney's Pan
116
·
With Sieves ..
85
Wheeler's Pan.
118
•
Dust Chambers
Union Grinder
85
120
·
The Discharge in Wet-Crushing.. 86
Moore's Quartz Grinder
120
•
The Grates
87
Gaston's Grinder.....
121
• •
The Screens
88
10. Pans with Conical Mullers.
6. The Feeding of Batteries.
Hepburn & Peterson's Pan..
121
Belden's Pan ...
122
The Hand-Feeding....
90
Baux & Guiod's Grinder.
122
The Stationary Hoppers
91
Movable Hoppers
92
•
Quantity of Water for Crushing..
11. Pans with Tractory-Conical Mullers.
93
Remarks on Speed and Weight of
Excelsior Pan..
123
Wheeler & Randall's Pan..
125
Stamps....
94
Excelsior Continuous Grinders
125
7. Reduction by Rolling Mills.
Construction of Rollers..
12. Pans with Perpendicular Mullers.
97
•
The Frame
99
The Centrifugal Ore Grinder
126
•
The Feeding of Rollers.
102
•
Varney's Quartz Grinder
127
III. CONCENTRATION.
Concentration of Reduced Ore.
Division.
A. Concentration of Ore Grains, (Jig-
The Principle
The Jigging..
ging Stuff.)
• •
2. Movable Jiggers.
129
The Movable Jigger
133
•
3. Stationary Jiggers.
The Hydraulic Jigger
136
130
•
•
Petherick's Separator
137
131
The Stationary Jigger
137
•
CONTENTS.
7
4. Continual Jiggers.
Page.
The Percussion Jigger (Setz-Herd) 139
The Continual Cylindrical Jigger. 143
The Continual Jigger.
• • •
The Sleeping Table.
The Rack...
The Sweeping Tables
The Round Buddle..
Page.
174
174
175
•
176
144
•
The Hydraulic Continual
145
The Concave Buddle..
176
•
· · •
The Blanket Tables
177
5. Rotary Machines.
The Rotating Cylinder (Strom-setz
9. Percussion Tables.
Maschine)
146
•
The Rotating Wheel (Setz-Rad).. 150
The Dolly Tub
151
Auferman's Dry Jigger....
The Percussion Tables....
The German Percussion Table.. 181
The Continual Percussion Table.. 183
Hunter's Continual Percussion Ta-
180
153
ble....
188
B. Concentration of Ore Sands.
Concentration of Ore Sands and
Varney's Percussion Buddle.
189
·
10. Oscillating and Shaking Tables.
Slimes
155
Borlase's Concentrator
191
6. Assorting of Sands.
Hendy's Concentrator
192
The Labyrinth.
Hungerford's Concentrator
192
161
•
Barron's Concentrator
193
Borlace's Slime Separator.
162
Ph. Hofmann's Separator.
163
Rittinger's Funnel or Pointed Box 163
11. Steady Moving Concentrators.
Rittinger's Spitz-Lutte
169
Steady Moving Concentrators....
194
Concave Rotary Buddle
195
7. Feeding of Concentrator.
Convex Rotary Buddle.
199
Feeding Boxes...
Burton's Table
200
169
•
The Stationary Feed-Box.
170
Self-Discharging Blankets
200
The Rotating Feeder...
Horizontal Moving Blanket.
211
171
18. Stationery Concentrators.
The Hand Buddle..
172
IV. SPECIAL CONCENTRATION.
1. Concentration of Gold Ores.
Concentration of Gold Ores... 205
Amalgamation of Gold Quartz.... 208
Amalgamation and Grinding
Combined Concentration and
Amalgamation ....
Treatment of Concentrated Stuff.. 212
209
+
210
2. Concentration of Silver Ores.
Concentration of Silver Ores...... 213
Cencentration Works..
Cost of Cencentration
Concentration of Tailings.
214
218
218
3. Concentration of Lead and other
Ores.
Concentration of Lead, Copper and
other Ores...
220
Value of Ores for Concentration.. 222
8
CONTENTS.
со
V. CHLORINATION.
Extraction of Gold from Sulphur-
Page.
ets or Arsenicals by chlorination 225
Assay of Gold Sulphurets by Chlor-
Page.
Lixiviation
247
The Precipitating Vat..
The Precipitation
248
•
• • •
248
ination
Chlorination Process for Sulphurets 230
Loss of Gold in Roasting
227
Cost of the Chlorination Process
per Ton of Ore
250
•
233
Remarks ....
250
•
Single Roasting Furnaces.
234
Double Furnaces
236
Mechanical Furnaces.
237
Other Methods of Dissolving and Pre-
cipitating the Gold from Sulphurets.
The Roasting Operation.
238
Roasting with Salt..
240
Chlorination.
Chlorination at Reichenstein.
Chlorination at Schemnitz..
Calvert's Method for Auriferous
Quartz...
253
•
•
255
•
256
Damping of the Roasted Ore..... 241
Sifting...
Production of Chlorine Gas....
242
244
Extraction of Gold, Silver and
Copper
•
257
I. INTRODUCTION.
SEC. 1.
Dressing of Ores.
Ores, as found in the mines, are generally impure to a con-
siderable extent, owing to an intermixture of foreign matters,
although concentrated deposits of pure ore irregularly dis-
tributed are of frequent occurrence. Veins, yielding mostly
pure ores, free from intermixed earthy matters or gangue,
and from which the metal can be directly extracted, are rare
exceptions. The great majority of veins contain the gangue
predominant. The gangue is not the only stuff which ren-
ders the ore impure. Many intermixed metallic minerals are
also considered as impurities, when they are not the object
of extraction, because either, under special circumstances,
they may have no value in themselves, or they may occur in
too small a proportion to pay for a separation, or the presence
of their metals may be prejudicial to the metallurgical or mill
process, causing loss of a more valuable metal, or making the
process more expensive.
The earthy portion of the ores, such as quartz, lime, heavy
spar, etc., is in some instances, to a certain extent, injurious
in their treatment by different metallurgical processes. In
every instance the expenses of reduction will rise with the
increasing proportion of the earths. This often happens to
such an extent that the working of the ore ceases to be pro-
fitable. Expenses of transportation, labor, fuel, fluxes, chem-
2
10
INTRODUCTION.
icals, power, etc., depend always more or less upon the bulk.
of the ore, which again depends principally on the relative
quantity of earthy matters.
The presence of metals in the ore, which are impurities,
considered with reference to a certain metal in view, is gen-
erally productive of much inconvenience in metallurgical
operations. One metal requires a different treatment from
that which suits another, and one may have a bad effect on
the quality and quantity of another which represents the
object of extraction.
The separation of valuable matter from its intermixture
with heterogeneous substances, is called the dressing of ores·
This term comprehends the mechanical separation generally,
that is, the separation of gangue and worthless material from
valuable ores, as well as the separation of the ores themselves
into different classes, according to different intended modes
of treatment; the separation of gangue from ore by means of
water is called concentration. Dressing includes concentration
as one of its most important parts. The object of the "dress-
ing of ores" is the separation of the worthless from the valua-
ble portions as closely as possible with the least loss and the
smallest expense. A very close separation is difficult and
not always advisable. The less value a mineral contains, so
much the closer may its separation from gangue be effected.
•
Concentration consists in washing off the poorer or worth-
less parts from the ore. Difference of specific gravity,* or at
least difference of the aggregate condition of the minerals, is
the requirement for the possibility of separation. If, there-
*With a gravity difference of about 14, as is the case between gold and the
gravel of the placer diggings, the concentration is so easily accomplished that the
most simple apparatus will give a satisfactory result, even with mixed material of
all sizes, provided there is no floating or very fine gold in the gravel. The cra-
dle, long tom, sluices, etc., are proper contrivances. The Chinese on the Island
of Borneo use the "kotok," a ditch 3 feet wide, 600 feet long, lined with oak lum-
ber, for the purpose of gold washing, very much in the same way as is done in
California in the sluices. The ditch breaks several times, changing its direction.
abruptly, in order to facilitate the deposition of gold, which is taken out after four
months' work.
INTRODUCTION.
11
fore, different minerals of the same specific gravity constitute
the ore, or if minerals of different gravity are combined
chemically, no mechanical separation can take place, but then
a chemical process is sometimes first employed to produce a
difference of specific gravity for the purpose of concentration.
So, for instance, tin ore is generally accompanied by wolfram,
molybdenum, arsenical-iron and copper pyrites, zinc blende,
copper glance, bismuth and antimonial ores, besides earthy
minerals. In Cornwall, Bohemia and Saxony, tin ores are
subjected to a concentration by means of water. The con-
centrated ore contains all the wolfram, which is but little
heavier than tin ore, most of the arsenical pyrites of nearly
the same gravity as tin ore, and much of the iron and copper
pyrites. This concentrated ore is then charged into a rever-
beratory furnace and roasted for the purpose of oxydizing
the arsenic and sulphur combinations, in order to change the
specific gravity. The roasted ore is again concentrated and
sometimes, if the ore is very impure, the roasting and con-
centration is again repeated. The wolfram and tin ore
remain unchanged-the former must be removed by a sepa-
rate smelting process.
The sorting of useful ores* into classes depends partly on
the presence of different ores in the same ledge, as is often
the case. For instance, silver ores, galena, zinc blende and
copper ore may be associated in such a proportion that sil-
ver, zinc and copper can be extracted to advantage. In this
case silver ore and galena must be separated from zinc blende
and from copper ore, or if silver should be extracted by
amalgamation, attention must be paid to the separation of
*The sorting of ores, with reference to the different metals they contain, is not
much practised in California and Nevada, for the reason that metallurgy here is
as yet confined principally to the ores of gold and silver-two metals, the separation
of which is not necessary, inasmuch as amalgamating or smelting is, in the most
cases, proper for both alike. Smelting of copper and lead ores is very limited as
yet. Much more in use is the sorting into classes of rich and poor ores of the
same kind. The rich ore is shipped away, or subjected to roasting, and treated by
a more expensive process; or, if worked by the same process as the poor ore,
more attention, time and chemicals are bestowed upon the work.
12
INTRODUCTION.
silver ore from galena. Mechanical sorting is often much
cheaper and simpler than chemical, which meets sometimes
great difficulties in producing a pure article out of compound
ores. Ores are also sorted for the purpose of classification
into rich and poor ore of the same kind. With proper work-
ing the per centage loss of metal of poor ores is higher than
of rich ores. It is, therefore, always advisable to separate
the rich from the poorer classes, if the character of the ores
permits it.
SEC. 2.
Principles of Dressing.
The dressing of ores is based on the following principles:
First-Each constituent of the mass must be brought to the
highest value which can advantageously be given to it.
Second-The useful minerals must be concentrated only to
the most advantageous degree of purity. Third-All loss of
the quantity and value of the useful mineral must be avoided
as far as practicable.
According to the first principle, we must endeavor to obtain
each mineral with its highest value. It is very often the case
that a deposit or vein carries different metallic minerals, for
instance galena, copper pyrites, iron pyrites, blende, cobalt
ores, etc., which, in an isolated condition, command a certain
highest price. If such ores were delivered unseparated,
then not only would the subordinate metals remain unnoticed
by the purchaser, but the value of the principal ores would
be depreciated to some degree on account of the difficulty
which would arise for the metallurgist in obtaining pure arti-
cles from the compound ores, being compelled to use a more
complicated and expensive treatment for that purpose. If,
however, these minerals were separated by dressing, the
INTRODUCTION.
13
principal minerals would come up to their respective highest
prices and the miner would also realize the value of blende
besides, if this be treated for zinc. The pyrites may be made
use of for the production of sulphuric acid, or the smelter may
need it for the concentration of the silver in the matte or for
roasting of silver ores which are poor in sulphur.
With regard to the second principle, it would seem that as a
matter of course, the purest stuff would prove to be the most
advantageous, but from a practical point of view it is differ-
ent. The concentration should be continued only so far that,
under the local circumstances, the most profit can be realized
from the concentrated stuff. The more precious the metal is,
the less advisable it is to concentrate it closely. There are
many particulars to be considered as to what constitutes the
most profitable degree of concentration. In this connection
must be considered:
1. The mining expenses on the ore or the purchase price
of ores or tailings, the hauling and all expenses on the
ore till delivered at the place of concentration.
2. The cost of crushing, including all expenses connected
with the work of concentration, transportation to the
reduction works, cost of water, etc.
3. The loss sustained by concentration.
4. The expense of reduction and loss of metal thereby, and
in what proportion the loss will appear with reference
to the more or less concentrated matter; and finally,
5. Whether the reduction, that is, the extraction of the
metal is effected in the same establishment or in cus-
tom works.*
*If the reduction is to be performed in a custom mill, the conditions must be
considered. In Nevada, for instance, it is the usage in some custom mills to charge
for amalgamation of silver ores, by way of roasting, $50 per ton, without reference
14
INTRODUCTION.
There seems to be a mistake in some places, as to the proper
degree of concentration, which misleads the inventors of con-
centrating machines as well as those who wish to make use of
concentration. The leading principle of these machines is
the extraction of pure sulphurets, and the putting through
of a large quantity of stuff in the shortest time with the
smallest apparatus under all circumstances. Mere turning
out the purest sulphurets, is by no means a proof of the best
contrivance, and can be looked upon often with suspicion of
losing a great deal of rich fine particles if present. Very
cleanly extracted sulphurets are often not only clean of earthy
matters, but also of silver sulphurets, fine amalgam, etc. In
some instances a close separation of sulphurets from earthy
or other injurious matters is a condition for the further eco-
nomical treatment of the educt. With sulphuret of lead,
copper sulphurets, etc., because of the low value of the metal,
a close concentration must be effected. Auriferous pyrites.
require to be concentrated as close as possible for the chlori-
nation process, unless the gangue is pure quartz, but it would
be a great mistake if silver ores should be subjected to a
close concentration.
to the compounds, returning 80 per cent. of the value in gold and silver found by
the fire assay. On account of distant hauling and the fixed charge, without refer-
ence to the richness, it might be more advantageous to concentrate closer. The
following calculation will show how the degree of concentration is limited. For
instance, a certain amount of ore or tailings is reduced by concentration to 10 tons
The value
(20,000 pounds) which would pay according to an assay, $150 per ton.
of these 10 tons, after deducting 12 per cent. of moisture, would be.....$1,320 00
Hauling, at $4; charges, $50 per ton (dry); deduction of 20 per cent...
Return...
744 00
$576 00
Supposing now the above 10 tons were reduced by further concentration to 5 tons,
and the loss by further concentrating supposed to be 20 per cent., the value of these
5 tons, after deduction of 20 per cent., concentrating loss of the value above stated
would be
.$1,056 00
་
Hauling of 5 tons, at $4; charges, $50 (for dry stuff); additional concen-
trating expense, $15; reduction loss, 20 per cent....
466 20
Return
$589 80
•
The difference of $13.80 is in favor of closer concentration; other circumstances,
however, may show a loss by over concentration.
INTRODUCTION.
15
As to the percentage which possibly can be obtained in
concentration it is not unusual to be assured by inventors of
concentrators, that they concentrate any ore within 5 or 10
per cent., an assertion the reason of which is either personal
interest or more probably inexperience, but the statements
are readily believed by customers. In the concentration of
lead ores, galena principally, conducted on the best princi-
ples with all the improvements of modern concentration in
Europe, where great attention and plenty of time are devoted
to the operation, the loss is generally from 15 to 20 per cent.
Saving 80 per cent. of lead ores in concentration may be con-
sidered a very satisfactory result. It must be borne in mind,
moreover, that galena occurs in cubes, the cleavage is also
cubic, very seldom fibrous, the specific gravity is 7.5-most
favorable conditions for concentration-while the specific
gravity of the principal silver ores ranges from 5.2 to 6.2, and
they have the disadvantage of assuming mostly a fibrous or
leaf-like shape when pulverized. The silver sulphuret is
heavier (7) but ductile. It is, therefore, quite proper to cal-
culate on a loss of 35 to 45 per cent. (including loss in crush-
ing) in treating silver ores, provided the plan for concentration
is a proper one.
How differently silver ore behaves from lead ores in con-
centration is shown by the result of a concave buddle §45 d.
The nature of the ore certainly modifies the loss to a consid-
erable extent. With the concentration of gold the case is
different; for its high specific gravity allows a more perfect
concentration, but, although under the most favorable cir-
cumstances from 90 to 95 per cent. of the gold may be saved,
there are also cases where 30 per cent. and more might be lost;
for instance, if the gold should occur in a very fine scaly con-
dition in a clayey rock. A man, though experienced in con-
centration, cannot give an approximate estimate of the
concentrating loss without having examined the nature of the
ore in question, for the reason that the loss depends not only
on the shape and gravity of the pulverized ore particles, but
also very much upon the character of the gangue.
16
INTRODUCTION.
It may, moreover, occur, that some earthy or metallic min-
erals mixed with the useful ore, may be desirable for the
reduction, so that a separation of the same would not only be
useless, but injurious, because the loss of the ore increases,
while the separation is going on, and because the ore may be
more valuable if such minerals are not removed.
Professor Gaetzchmann mentions the following metals and
minerals as injurious or otherwise, with reference to the
metal which is the object of extraction: "Iron and copper
pyrites, and apatite, in iron ores (copper often accompanies
spathic iron), while on the contrary spathic iron is not injuri-
ous to copper ores (other sorts of iron ores are not desirable
with copper ores). Iron, copper, arsenical pyrites and zinc
blende, injure tin; bismuth makes its color dull; copper
makes it brittle. Arsenic makes lead brittle; antimony
hard. Lead with carbonate of zinc (galmey) or with blende,
spoils the zinc. Lead must be carefully separated from all
kinds of ores out of which copper is to be extracted by pre-
cipitation or silver by amalgamation. In the first case, it
makes the copper impure; in the second, it enters the quick-
silver, and causes a greater loss in silver. Nickel-speiss
(impure arsenuret) injures the amalgamation of silver ores.
Injurious to cobalt (for the purpose of manufacturing blue
paint) are calc-, brown- and manganese-spar, horn-stone, fer-
ruginous quartz and galena. Nickel imparts, only when pre-
dominant, a red tinge (arsenic, on the contrary, intensifies the
cobalt, and renders the color agreeable). Mica, lime, garnet,
augite, and horn-blende, promote the fusibility of magnetic
iron ore; fluor spar facilitates the smelting of lead, silver
and copper ores. Spathic iron and heavy spar are advan-
tageous in smelting lead ores; iron pyrites is useful for the
production of matte."
In treating unroasted silver ores in iron pans, antimony is
objectionable. If chemically combined with silver, it pre-
vents the amalgamation of silver ores more or less. Thirty
per cent. of antimony (as a constituent part of the mineral)
makes roasting indispensable. As a sulphuret, antimony
INTRODUCTION.
17
amalgamates under certain circumstances, especially if talc is
present in the ore, and forms a bulky amalgam of sulphuret of
antimony, causing a great loss in silver and gold. For simi-
lar reasons arsenical pyrites is injurious to silver and gold
amalgamation. Carbonate of lead must be carefully separated,
it being easily decomposed. Galena is also decomposed, but
with difficulty. Clay, talc and talcose slate deter amal-
gamation, causing also a greater loss in quicksilver. Calc
spar is favorable; iron, copper and zinc sulphurets are indif-
ferent.
Talc is also injurious in auriferous pyrites, if this be sub-
jected to the chlorination process, for the purpose of extract-
ing the gold. The talc in the chlorination tub absorbs too
much chlorine gas. It is, therefore, necessary to roast such
stuff with from 1 to 5 per cent. of salt, according to the
amount of talc.
In relation to the third principle, it is evident that a separ-
ation or concentration cannot be performed until the ore is
reduced to some degree of fineness. During this process a
certain loss cannot be avoided; this loss must increase with
the fineness of the pulverization. The loss in the quantity of
the educt arises from too close, and the loss in the value from
insufficient concentration. It appears, therefore, most advis
able to pulverize and to concentrate the ore only to such a
degree as absolutely necessary. The dissemination of the val-
uable matter in the rock in coarser or finer condition, is the
guide as to what degree of pulverization is required. It is
utterly impossible to prevent all loss in pulverizing the ore,
but with sufficient care and proper management this loss may
be reduced to a minimum. Much handling of the pulverized
ore also occasions loss.
In order to carry out these principles a proper choice and
succession of operations must be determined upon before
hand, the important conditions in which are the following:
The ore must be subjected only to so many and such oper-
ations as are absolutely necessary to accomplish the purpose.
Such methods must be adopted as are in accordance with
18
INTRODUCTION.
local circumstances and the quality of the mass. The follow-
ing points must here be considered: The nature of the mate-
rial, that is, of the useful mineral, of the gangue and of the
country rock of which some is generally broken with the ore.
Also in what condition the ore appears in the rock, whether
disseminated in coarse particles or in coarse pieces, or only
coating the rock in thin layers as is the case with chloride of
silver, native silver, etc. Also the structure must be exam-
ined, the cleavage, toughness, hardness and what size and
shape the mineral assumes when crushed.
(a.) Cubic galena, iron and copper pyrites, for instance,
require different and more simple operations than fibrous
galena. Ore of the same kind, with only one sort of rock, is
more easily separated than if mixed up with various rocks, as
quartz, heavy spar, feld spar and lime. Native gold, cop-
per and silver hammer out into leaves or flat pieces, while
galena, iron and copper pyrites form granular particles-the
latter, therefore, concentrate more perfectly. Ruby silver,
brittle silver ore, blende and gray copper ore concentrate more
difficultly, assuming a less favorable shape after crushing.
(b.) Unfit for concentration, or very difficult, are decom-
posed silver and other ores, especially if easily converted into
powder; malachite and argentiferous carbonates of lead and
copper, so often found in Nevada, Montana, etc.; chloride of
silver, native silver in leaf or scale shape, plumbic ochre, cin-
nabar, etc.
Quartz, heavy spar, gray wacke, admit the precipitation of
ore particles more easily than talcose or clayey rock, clay
slate or gneiss. Great care must be taken not to disperse or
scatter the ore particles in the mass by fine crushing, or by
still more injurious grinding.
It is difficult to effect the separation of blende, copper, iron
and arsenical pyrites and heavy spar from silver ores, wolfram
from tin ores, chlorite and epidote from copper ores, spathic
iron from copper pyrites and galena.
Pan tailings from unroasted silver ores are often subjected
to concentration for the undecomposed sulphurets. This
INTRODUCTION.
19
material contains a great deal of metallic iron partly from the
stamps, but principally from the shoes and dies of the grind-
ing pan. The iron of such tailings, if exposed to the air for
several weeks, will oxydize, and in connection with other iron
particles form light voluminous little bunches, involving sul-
phurets and amalgam. These very numerous voluminous
particles cannot be retained with the heavier clean sulphur-
ets, no matter what method of concentration may be adopted,
but flow off with the water before the sand. If, therefore,
valuable tailings are intended for concentration, which could
not be executed immediately, they should be kept under
water.
According to the preceding, it is obvious that a proper
conduction of the dressing requires a knowledge of the phys-
ical and chemical nature of the metallic and earthy minerals,
and of the value and richness of the orey matter; knowledge
of the particular metallurgical treatment, to which the ore is
to be subjected is also required, in order to be able to judge,
whether the cost of a closer concentration would be justified
by the advantage which the metallurgist would derive there-
from, while also taking into account the mining expenses,
which augment or reduce the quantity of concentrated mat-
ter. It requires practice on the part of the operator and
conscientiousness that he may be aware of the real amount of
loss suffered by dressing, and know all contrivances of ascer-
taining the same. The inventors of concentrating machines
are often unscrupulous enough as to the resulting perform-
ance of the concentrator, and frequently deceive themselves
for want of experience.
20
INTRODUCTION.
SEC. 3.
Division of Dressing.
In accordance with the nature of the operations, the dress-
ing of ores must be divided into two parts:
1.
The Dry Dressing.
2.
The Wet Dressing.
The dry dressing chiefly comprehends the sorting of rock
with reference to the different minerals it contains, and the
separation of the useful part from the gangue by hand, judg-
ing from the external appearance of the ore. This separa-
tion is generally done by hand and is, therefore, limited to
pieces such as can be conveniently embraced by the eye.
But in some instances also pulverized ore is subjected to a
dry concentration, on principles common with wet concentra-
tion, substituting compressed air for water.
In the wet dressing the separation is performed by means
of water. Here the useful mineral is generally so minutely
disseminated that a separation by hand would be impossible.
The wet dressing, therefore, is applied to ores in which the
useful particles are minute, often hardly visible, and in such
small proportion that without concentration the ore would be
worthless. But it is not applicable to masses, in which the
shape of the mineral prevents its sinking in water, or offers to
the motion of the water a large surface having a very small
weight. Such minerals are kept suspended in the water and
carried away.
The matrix of such ores is generally found in a compact
state, excepting in case of alluvial deposits, in which gold,
platinum, tin ore and gems occur. It is, therefore, necessary
to reduce the rock to a proper size before any separation can
INTRODUCTION.
21
·
be undertaken. For the purpose of dry dressing, the ore is
broken into rough pieces; while wet dressing, particularly
concentration on tables, renders fine crushing necessary.
Besides the reduction to a smaller size, there are other auxil-
iary operations in use to promote the dressing:
1. The washing of the muddy vein stuff, brought to the
surface, in order to clean the mass for the succeeding treat-
ment. This precedes both the dry and wet dressing.
2. Another operation, preceding sometimes the entire
dressing, or succeeding a part of it, as preparation for further
treatment, is the burning or roasting and decomposition by
exposing the ore to the air, either for the purpose of render-
ing the rock brittle, or of changing the specific gravity of
some mineral.
3. The amalgamation (of gold). The separation of gold from
gangue by means of quicksilver, being performed mostly by
mining superintendents, is generally claimed as a part of the
dressing, although the metallurgist considers amalgamation
as a part of metallurgy. In California and Nevada, where in
most mills quicksilver is introduced into the battery for the
purpose of separating the gold from the gangue, while the
reduction of the rock is going on, the amalgamation certainly
belongs to the dressing department. In Nevada, however,
the pulverized stuff is treated in iron grinding pans for the
amalgamation of silver and gold. In this case a mere contact
of silver ore and mercury is of no avail, inasmuch as a chem-
ical action is required by which silver sulphurets shall be
decomposed, in order to admit amalgamation. Under these
circumstances, the amalgamation also of unroasted ore is a
metallurgical process.
4. The cementation, for the extraction of copper, from
washed cupriferous tin ores.
22
INTRODUCTION.
}
5. The treatment of washed tin ores with acids or alkalis,
in order to remove bismuth or wolfram.
6. Another auxiliary operation is the use of the magnet and
electro-magnetic apparatus, for extraction of magnetic iron
ore and metallic iron from gold, tin, and other concentrated
ore.
ores.
These are the general proceedings in the way of dressing
As a matter of course, however, the choice of the pro-
per dressing operations must be regulated according to cir-
cumstances, which differ largely even in one and the same
district. In the States, for instance, certain rock, which con-
tains the ore in coarse and fine particles, may be treated
advantageously by a very coarse crushing and subsequent
jigging, in order to save the coarse ore particles from further
reducing (partially to floating ore) and then the jigging refuse
be subjected to fine crushing and concentration on tables. In
California, Nevada and, especially, Colorado, Montana, etc.,
the fine crushing from the start would be a more economical
treatment of a like ore, although a greater loss is a sure con-
Circumstances will also decide whether concen-
sequence.
tration should be used before the ore is subjected to the pan
amalgamation or after. The dressing of ores for smelting
purposes, where each particle of the rock, besides consuming
fuel and flux, has an influence on the result of the smelting,
either advantageous, assisting the fluxing, preventing the
scorification of metals, etc., or disadvantageous, causing a
greater loss, or rendering the smelting more expensive, must
be differently and more carefully performed than the dressing
of ore for amalgamation in pans, where the earthy matter
interferes but little or not at all with the process. But even
in the latter case, it must be remembered not only that the
wear of iron and use of chemicals must increase to no purpose
if too much earthy matter is present, but also that the per-
centage mechanical loss of amalgam and mercury will rise
with the increase of useless minerals. For a similar reason
INTRODUCTION.
23
to the one last mentioned, lead ores must be brought to a
higher degree of concentration than other ores, in order to
diminish percentage loss in the smelting of a metal which is
so liable both to volatilize and slag. Gold quartz, containing
only free gold, a metal which, owing to its high specific grav-
ity, is much more easily concentrated than other ore, provided
that no mercury is used in the battery, and that the gold does
not appear in fine scales, can be treated by more simple con-
centrating arrangements, even when the quartz could be
treated by amalgamation with some profit without concentra-
tion. The working of the bulk would require, for instance,
six or eight iron pans, the interest on the cost of which, the
renewing of shoes and dies, etc., would cause expenses much
heavier than the loss of gold suffered by concentration, after
which only one pan may be sufficient to extract the gold.
The dry dressing operations do not present so many deli-
cate points as the concentration, are easier controlled, and
executed with less loss. There are no such expensive pre-
parations required, but the result depends entirely on skillful
dressers, who are able to judge of the valuable parts of the
ore by sight. To what extent the dry dressing is advisable,
depends on many local circumstances, but principally on the
price of hand labor. In Europe lead ores are subjected to
extensive handling by men and children; also in Mexico
labor is low enough to admit a profitable separation of ore
from gangue, while wages in California limit the dry dressing
to only superficial separation. This is still more the case in
Nevada, while in the more remote Districts and Territories,
where a man is paid five to six dollars per day, the dressing
in the mine must be reduced to mere separation of entirely
worthless rock from the ore, and everything as far as practi-
cable be performed by steam or water power and machinery.
24
INTRODUCTION.
SEC. 4.
Separation of Gangue from Ore in the Mine.
Ore bearing lodes cannot be worked without breaking more
or less from the walls. In many instances a part of the wall
must be taken out purposely, sometimes to prevent wastage
of very valuable ore or gold quartz, sometimes to give addi-
tional space when the lead has a smaller size than is conve
nient for working. Ledges of large size will always contain
gangue or boulders of useless rock, the hoisting of which
increases the mining expense; sometimes it happens even
that such rock must be moved back into the mine in order to
fill up dangerous places. It is for this reason a judicious rule
to retain all barren rock in the mine for the purpose of filling
up places already worked out. The separation of the ore from
adhering wall rock and gangue is the beginning of dressing,
which is often not extended further in the mine. But some-
times also a separation of different classes of ore is performed
within the mine, especially if the lode is found in a decom-
posed condition, exposing rich streaks of uniform loose char-
acter, or deposits of solid rich sulphurets. In many mines, it
is the custom to assort the rock not only in regard to useless
gangue, richness and variety of ores, but also with respect to
the different kinds of rock in which the ore occurs, if these
are distinctly marked, and it can be easily done. In parting
worthless rock, a mistake may easily occur in decomposed
*By the expression "worthless rock," it is not intended to convey the idea that
a rock or gangue is perfectly free from metal. This expression is applied to all
ore from which no profit can be realized in any way. There can be no general
standard as to how poor the ore may be before it is declared worthless. It is
different with the ore of each different metal, and with different ore of the same
metal. It varies also with working facilities, labor, etc. While, for instance,
silver ores assaying $10 per ton in most mines may be considered worthless; in
other districts ore assaying $20 per ton is worthless, and not excavated. The
total expense on the ore of a prominent claim on the Comstock lode (Nevada)
was, in 1865, $32 per ton. Counting the loss of extraction, the ore should assay
at least $40 to cover all expenses, leaving, even then, no profit.
INTRODUCTION.
25
veins, where there is no difference to the eye between poor
and worthless, especially with gold ore, or when the loose
stuff is intermixed with dark spots of clay, slate, etc. It is
then important to examine the waste rock every day carefully,
by washing or assaying, not relying on the known appearance
of the rock, as its character might unexpectedly change,
while retaining the same exterior appearance. It is certainly
of much importance to be always well posted as to the value
of the rock within the mine-a knowledge easily obtained by
frequent assays, or by the use of a horn-spoon, or pan. The
tin miner is often guided entirely by the result of his wash-
ings of the pulverized samples. It is often advisable to
excavate also such poor ore, as for the time will not pay for
extraction, especially in new districts where expenses are
very heavy-a condition which will change in a year or two,
allowing then a profitable treatment of poor ores.
Generally within the mine, the separation is confined to a
mere superficial parting of the rock from orey stuff. Defici-
ency of light, and its deceptive effect on the looks of the
ore, and finally the muddy condition of the rock, are the
obstacles to a close separation. Washing off the mud is not.
practicable in the mine, except with rich gold specimens, in
order to keep such valuable ore separate. The separation of
gold-bearing from entirely barren quartz, in case only a cer-
tain stratum of the whole mass is paying rock, is frequently
difficult, for the reason that both parts are very much alike.
Often, however, the pay stratum differs from the worthless,
compact, or flinty, generally white quartz, by assuming a
slaty appearance, intermixed with thin layers of slate or clay,
with a red or brown color, etc.
In order to effect a separation, the vein rock must be
broken, but only to a size convenient for handling. The
breaking is performed by steel sledges, of varying weight,
according to the quality of the rock, from eighteen to
twenty-five pounds. Both ends are alike and square-faced,
and the sledges are provided with long handles. A great
deal of rubbish or smalls is produced in breaking, and must
3
26
INTRODUCTION.
be saved with more care, the richer or more valuable the
ore is.
The result of dressing within the mine gives four classes
of rock, or less, according to circumstances. First-Worth-
less material, either remaining in the mine to fill up excava
tions, or brought to the surface on the waste heap. Second-
Rich ores, when circumstances require the separation under
ground. Third-Middle ores, to be dressed outside; and
Fourth-Smalls resulting from breaking.
SEC. 5.
Dressing of Ores Outside the Mine.
On arriving at the surface, the ore is still intermixed with
rock and gangue which could not be separated from it in the
mine. Generally the ore is discharged on a level ground as
close to the mine as possible, in order to save the transporta-
tion of waste rock. The principal object here is the continu-
ation of dressing by ragging, spalling and cobbing; also
washing and sizing.
SEC. 6.
Separation by Hammers.
A. The Ragging is performed by steel-headed ragging
hammers, from six to eight pounds weight. In this opera-
tion, breaking the rock smaller, a part of it and of the gangue
is rejected; the balance turned over to spalling, a further
continuation of the same work. Although the ragging is
only a preparatory breaking, the ragger must pay attention
not only to the separation of worthless rock, but also to a
rough classification of concentrating, smelting and amalga-
mating ore, and accordingly he delivers two or more classes to
INTRODUCTION.
27
B: The Spalling.-The ore is broken by the spaller to
still smaller pieces, of such size as may be required, for
crushing of concentrating ore, and for cobbing of the
separated ore. The spalling is performed by hammers of
cast steel, of about two pounds weight, on long handles.
The poor part, separated by spalling, is designed for crush-
ing and concentration. This class of ore must be carefully
separated from worthless stuff, as well as from ores too rich
for that purpose. If the ore is composed of very hetero-
geneous matters requiring different treatment in crushing
and concentration, the separation must be executed very
attentively while spalling. Mistakes which occur now, can
not be remedied after crushing, or only with much more
difficulty, and with more loss. The spallers must be able
to judge the quality of the ore. The separation must be
performed more carefully than in the former operation;
but it depends on the nature of the ore, and on the mode
of reduction, into what classes the ore must be separated.
Clay, quartz, heavy spar, and limestone, must be differ-
ently treated. If mixed, they cause a greater loss of ore in
concentration than when separate. If the concentrated
ore is subjected to smelting or amalgamation, it is some-
times important to have lead separated from copper, tin
from pyrites, or blende from other ores. In other instances,
lead and copper must be separated from silver ores. Accord-
ing to such and other circumstances, the sorting must be
conducted while spalling.
It is also the usage to separate the ore intended for cob-
bing into classes of different metals in a superficial way.
This the spaller should execute in such a way that one of the
important constituents should always prevail in the respect-
ive heaps.
If all the ore were transferred to the cobber
in one pile, it would be impossible for him to effect the
separation into different sorts, or, at least, it would be
done very imperfectly, his attention being too much divided.
It is, therefore, always so arranged that the dressing pro-
gresses gradually through all the operations, beginning in the
28
INTRODUCTION.
mine and ending with the cobbing, or, as the case may be,
with the concentration. The spalling is not very fatiguing;
and hence boys and women are frequently employed in
Europe to do the work. The result of the spalling is similar
to that of the preceding ragging and the following cobbing.
The worthless part is turned out on the waste pile, the con-
centrating ore carried to the concentration works, and the
separated ore delivered to the cobbing.
SEC. 7.
Continuation.
The Cobbing. The cobbing is executed by boys, who are
carefully instructed in the particulars they have to perform..
The work is done by cobbing hammers of different shapes,
from one and a half to two pounds weight, fixed on short
handles. One end generally presents a square face; the other
is sharp-edged. The latter form is required for detaching
poorer parts from the ore without smashing the better. A
regardless pounding is not tolerated; it would form too much
powder, preventing at the same time a separation, if needed.
The cobbing is the continuation of the spalling and the
finishing of the dressing of that part of the ore which is
delivered to the reduction works. A great deal of attention
is therefore required to perform the separation properly.
As before mentioned, the ore, when brought to the cobbing,
is already classified to some degree, and this classification
must be continued by the cobber on the same principle, only
more minutely. Very little waste rock falls off in this oper-
ation. One part is obtained for concentration. The smalls
generally pass to the jigging, or are transferred with the
best class to the reduction. The amount of metal in the
picked ore is very different, and depends on local circum-
stances and the mode of reduction. The dressing must be
always based on the principle "to separate the ore to the
INTRODUCTION.
29
best paying condition." Picked lead ores, for instance,
in some places are considered sufficiently well dressed when
they assay 30 to 40 per cent. of lead; in other places from
50 to 65 per cent. If silver ores occur with the lead ores, or
if silver ores have to be smelted with lead ores, it is proper
to dress the latter to a higher percentage of lead. Copper
ores can be dressed to a lower degree than lead ores, and so
forth.
The cobbing is executed either on iron dies, from nine to
twelve inches in diameter, or stone pieces shaped in a square
form. The stone dies are preferable only in cases where iron
particles are injurious to the ores; for instance, in treating
tin or cobalt ores. The dies are fixed either on the floor or
on benches. In some places, the picked ore is broken as
small as required for smelting; but generally it is reduced
smaller, or pulverized by machinery. The poorer portion
for concentration is usually broken in pieces of about eight
cubic inches, more or less, according to local circumstances.
Very brittle and hard rock suffers more wastage in breakage.
For that reason there are square iron rings in use in Corn-
wall and Germany. The rings are six inches square, and
four to six inches high, one side having a handle. They are
placed over the dies if needed. Also a small hoe is handy,
in order to keep the dust and smalls together. The cobbing,
although not requiring much strength, is, nevertheless, a tire-
some work. It is, therefore, necessary to arrange everything
for the workers as comfortable as possible. A bodily torture,
caused by sitting on the floor while cobbing, depresses the
mind, the effect of which is always disadvantageous to the.
employer. The climate is another point of consideration
where the winter is severe, the cobbing must be performed
in well-built houses, with sufficient light and circulation of
air.
The cobbing bench at Freiberg (Saxony) has the following
arrangement: Alongside the walls of the building, there is
a wooden frame, three feet high and the same width. The
front is lined with planks, not perpendicular, but inclining
30
INTRODUCTION.
downward towards the wall, in order to get room for the cob-
ber's feet. Inside the lining, it is filled with loam, well stamped
to the brim of the frame-work, forming thus a long bench,
the top of which is parted by twelve-inch high partitions
into spaces from three to four feet wide-sometimes a little
wider for each cobber, or for two. The dies, one or two in
each place, are placed so that one inch and a half projects,
while the other part is stamped in from all sides, rendering it
immovable. A flooring is then laid over the whole length of
the bench, leaving the projecting dies exposed for use. In
front of the bench is a beam, supported by uprights and
braces, called the "sitting tree," although used more to lean
upon than as a seat, for the reason that standing cobbing is less
tiresome. For every two partitions there is one window,
protected by wire grates. The central part of the stone-
paved building receives the ore, and serves sometimes also
for spalling. The boys employed are between twelve and
fourteen years of age.
On the Pacific coast, the dry dressing is yet limited to a
separation of the ore into two classes, one being rich enough
to pay for reduction by some process; the other is considered
refuse, at least for the present. There is no third class
selected for wet concentration. Generally only the leading
metal is the object of dressing; other constituents are not
regarded, unless they occur in such quantities that they can
be made useful without concentration.
At New Almaden, (California) the experiment has been
tried of concentrating poor quicksilver ore by jigging. The
same process has been used to some extent with copper ores
at Copperopolis. As minute a dressing of ores as is exe-
cuted in Europe would not answer now on the Pacific coast;
but an entire neglect of dressing is liable to ruin a mining
enterprise. It has often occurred, that in consequence of
*
*There is certainly great difficulty, if not impossibility, in effecting a separation
on a dump, owned sometimes by different parties, or where from 200 to 250 tons
of ore are discharged daily on dumps of limited extent, as is mostly the case on
the claims of the Comstock, in Gold Hill; but a steady continuous income from
INTRODUCTION.
31
carelessness on the part of mining superintendents, waste
rock has been transported with the ore to the mills five or
six miles off, so that the ore, being poor by itself, could not
cover the expenses; and such ore is sometimes worked for
one or two weeks, or more, before it is discovered that the
mill is running into debt.
SEC. 8.
Separation by Hand.
The Picking. No breaking of rock is required in this
work, which is simply the picking of paying ore by hand.
Frequently the picking is combined with the cobbing, as is
sometimes the ragging with the spalling. The principal
material for picking is the smalls of the mine and the rub-
bish from ragging and spalling. In other cases, the smalls
are turned over directly to the concentration, or if the min-
eral is valuable, but so disseminated in the rock, that pick-
ing is not practicable, the smalls are delivered either to
the reduction or to the jigging-concentration.
As there is no breaking, or at most very little connected
with the picking, care must be taken to have all pieces larger
than a man's fist rejected from the smalls. Another mate-
a well managed mine, where the excavation of ore is carried on in proportion with
the facilities of an appropriate dressing and reducing, secures a better property
than a mine worked on an extravagant, so-called robbing system, regardless of
the future of the mine, and involving the unavoidable and multifarious losses con-
nected with all overdone work.
It is also due to the unfavorable proportion of small dumps and large quantities
of ore, that frequently ore boulders of from one to two cubic feet are forwarded to
the mills, containing always some waste rock, which usually consumes besides the
hauling also the expense of reduction. Whether the reduction is performed in
custom mills or not, the mine has to bear the loss caused by defective dressing in
every instance. The custom mill is paid by the ton. It is therefore immaterial
to the millman whether he pays the hauling for poor or for rich ores.
He gains
more by two loads of rubbish than by one load of good ore; consequently the
mine is the loser on undressed ore, and, if nothing else, ragging ought to be per-
formed on all claims, combined with rejecting of easily recognizable worthless rock.
32
INTRODUCTION.
rial, subjected sometimes to picking, is the coarser part of
crushed ore for jigging. There are mines in Europe, for
instance, in Bohemia, Germany, etc., where from two hundred
to three hundred boys in one building are employed in pick-
ing. The proceedings in this operation are about the same
as in cobbing; but, as the smalls do not undergo any prepar-
atory assorting, the amount of waste rock is proportionately
larger than is obtained in cobbing. Besides the waste rock,
the picking gives a first-class ore for reduction, a second for
concentration, and a third class for jigging. The smalls from
the mine are generally muddy, and are washed either before-
hand or on the picking table; but in every instance it is
necessary to have the smalls sized. Dry stuff must be
wetted on the picking table, partly to wash off the mud, but
chiefly to expose the metallic parts, although some earthy
matters, as clay, slate, etc., assume also a dark color when
wet, rendering the picking uncertain if silver sulphurets are
present. In this case no water is used if the material is
clean.
The picking is performed on tables, around which the
workers sit. The proper shape of a picking table must
answer the purpose also of conveying the water, which is
sprinkled on the smalls out of the way, not interfering with
the pickers. Generally the platform of the table is slightly
inclined towards the center from both long sides, forming a
trough in the middle of the table of its whole length. A
steady supply of smalls directly from the sizing apparatus or
a feeding shoot to the pickers, has been successfully tried
and introduced at Lauenthal (Germany), by means of a cir-
cular rotating table, provided with radial-shaped boxes,
movable on an axis, and arranged on the periphery of the
table, which latter, slowly revolving, carries the boxes in a
circle, corresponding with the circular picking places beneath.
The picker, taking hold of a box, tips out the contents,
which, of course, must be picked over while the supply-
table makes one revolution. The box, having its support on
the axis, a little out of the centre of gravity, assumes its
former horizontal position again.
INTRODUCTION.
33
In other places, the moving table is also the picking table,
carrying the workers around, so that each one passes the
continually supplying sizing apparatus.
SEC. 9.
Washing and Sizing.
The ore, as before mentioned, on arriving at the surface
from the mine, is frequently coated with loam or clay or
other impurities, making a separation of ore from useless
stuff impossible. It is, therefore, in such cases, necessary to
clean the surface by means of water before subjecting it to
the already described operations of cobbing or picking. The
washing is generally combined with "sizing "-an operation
by which the ore is separated into different classes of
respectively equal size. Ore of larger size can be washed
simply by pouring water over it; but the smalls, being com-
posed of all possible sizes down to the finest slime, require a
more careful treatment. All pulverent matters have to be
separated from such stuff as can be handled and picked.
The greatest part of the former is suitable for jigging.
Before the introduction of jiggers, the pulverent part was
transferred either to the reduction or to the concentration
works, although generally either too poor for the first or too
rich for the last operation. Since the introduction of jiggers,
however, the ore particles are extracted first, then the whole
of the residue turned to the concentration. Machines for
washing and sizing can be divided into stationary and
movable.
SEC. 10.
Stationary Apparatus.
A. The Sluice.-Sluices are generally used for the purpose
of washing. They are differently constructed in regard to
dimensions, but all agree in having a trough-like form.
34
INTRODUCTION.
Where water is scarce, the sluice is closed up at the lower
end for several inches in height, so that the water is kept in
until the smalls are washed clean; after which the water is
discharged, and a fresh charge introduced. If there is suffi-
cient water, the washing is performed under a constant flow.
The sluices are from one to two feet deep, having about the
same width, and from four to ten feet long. Some are
made wider at the top than at the bottom. The washing
under a sufficient head of water, as executed on placer gravel
in California, is very effective in yielding a great deal of
clean stuff. Two or three washers rake the smalls for some
time, discharging the clean part continually, while the charg-
ing is kept up in the same proportion. The sluices require
to be sufficiently inclined, except those worked without a
permanent flow of water.
B. The Kiln.-This arrangement does the washing and
sizing at the same time, and is constructed in various ways.
An effective apparatus in England consists of a platform, on
the bottom of which is a cast-iron perforated plate, the holes
being one and one-fourth inches at the top and one and a half
half inches at the bottom. The plate is four feet by three
feet six inches. A large hopper is fixed at one end of
the platform, in which the ore is dumped. From a launder
above, a stream of water falls on the ore inside of the
hopper, and another on the ore on the perforated plate,
where a washer stands, raking the ore to and fro, until all the
finer stuff is raked through the holes. The coarse part is
drawn forward on the platform, and picked over by children,
who throw all the waste into wagons on rails. What falls
through the perforated plate, glides into a trommel beneath,
containing sieves of different degrees of fineness. The sized
stuff passes into compartments, in order to be treated sepa-
rately for concentration.
C. The Step-Sluice.-This machine is used in Germany,
Hungary, etc., in different modifications. The following
description will explain its general character: A sluice,
INTRODUCTION.
35
one and a half to two feet wide, and about fourteen feet long,
rests with an inclination of two inches or more to the foot,
on a solid frame. The sides twelve inches high. and the
bottom are made of planks. Between the sides there are
horizontal sieves or grates, 4 to 6 in number, fixed in a step-
like manner, somewhat inclined towards the front. The
holes or openings decrease in size from the head of the
sluice downwards.
Each of the plates or sieves are shut up on the front side
by a vertical cross-board. At the head of the sluice, above
the first grate, there is a feed box, or hopper, with a slide
door, through which the smalls are drawn upon an inclined
platform of several inches length, from which the washer
rakes his stuff upon the first sieve. At the head of each
sieve is a similar space, on which the stuff falls from the
coarser sieve above, before it is raked on the one below. At
the lower end of each sieve on one side is a discharge open-
ing, through which the coarse part of the stuff is drawn
after it is washed, either directly on the picking table or to
the jigging. Above the sluice, at a proper height, there is a
water pipe, or trough, supplying each sieve with a shower of
water through a pipe provided with a rose at its end. The
discharge opening may be arranged alternately on each side
of the sluice, according to convenience. A washer stands at
the side of each sieve, at a proper height.
The boy at the first sieve nearest to the hopper draws a
proper charge of smalls, rakes it on the grate to and fro
under the shower of water, draws a new charge, and contin-
ues to wash, discharging, from time to time, the clean part
through the opening. The smaller ore which fell through
the grate comes now on the second sieve, where it is treated
in the same way, providing the third sieve with still finer
stuff. Below the last sieve there is a gate, which is closed
while washing is going on, in order to arrest the sand. The
slime is conveyed into cisterns. The inclination of the sluices
amounts to about twenty degrees. This mode of washing
and sizing requires too many hands, especially if the sluice
36
INTRODUCTION.
contains six or more sieves. If more sieves are in use, it is
not necessary to have a stream of water above each, but only
so far as the smalls appear muddy.
SEC. 11.
Movable Washing and Sizing Machines.
There are many arrangements belonging to movable sizing
apparatus, varying in their construction from the simplest
hand riddle, to a complicated system of sieves and drums.
There are, also, machines, though these are of less import-
ance, the principle of which is a stirring by horizontal or
vertical stirrers, for the purpose of washing.
A. The Hand Riddle is the simplest sizing and washing
machine. It is still in use, especially with rich ore. The
hand riddle is made of various sizes and material. Some
consist of an oak hoop three-eighths of an inch thick and six
inches deep, the diameter ranging from eighteen to twenty
inches. Others are made of wooden staves, iron-hooped, or
of sheet-iron. The bottom consists of mesh work of iron
wire grates or punched sheet-iron. The washing is usually
performed in a tub, somewhat larger than the riddle, filled
with water. The riddle being charged with smalls, is moved
in a circular way until the smalls appear with a clean sur-
face. The work is very tiresome. For that reason different
mechanical contrivances are applied, by which the worker is
relieved from lifting or holding the whole weight of the
charged riddle.
B. The Rocker.-The rocker, or cradle, another well
known apparatus, (in California and Australia used as a
gold-saving machine) is preferable to the hand riddle, espec-
ially if a constant stream of water is conveyed upon the
INTRODUCTION.
37
rock in the sieve. This instrument is so familiar that a
minute description is superfluous. More effective than the
rocker is
C. The Circular Hand Riddle.-The cylindrical or circular
hand riddle is constructed of punched sheet iron or of a
wire sieve, the holes being three-fourths of an inch to one
inch square. The riddle is in the form of a drum, resem-
bling a coffee roaster in an inclined position. It is turned
by a crank at the lower end, while the coarser smalls pass
longitudinally through the riddle into a shoot. The sand,
falling through the sieve, is conveyed into compartments.
It is used in the Cornwall mines. This circular and the
common hand riddle, as well as the rocker and many other
contrivances using one sieve, are not very efficient, for the
reason that only one sort of stuff is obtained free of pulverent
matters. Superior to these are the following machines:
Swinging and Jarring Riddles.
This class of riddles (German, Raetter) comprehends a vari-
ety of arrangements, all having motion and suspension. The
motion is applied differently, either simple swinging, and
percussion, horizontal, longitudinal, or vertical. They are
extensively used, not only for washing and sizing smalls, but
also in connection with rollers or crushers, in order to size.
the ore properly for jigging concentration.
The same
arrangement is also used in coal mines for the purpose of
separating coal smalls.
The swinging riddle has an oblong square shape, with a
rim about six inches high on three sides, the front being
open for the discharge. The bottom is formed principally
by a sieve. The upper part is covered with an iron plate;
the lower is also solid, and lined with sheet iron, leaving the
middle part of the bottom for the sieve. Sides and bottom
are made of plank; sometimes entirely of iron. The sieve
may be wire cloth. perforated sheet or cast-iron. The holes,
38
INTRODUCTION.
it may be remarked here, are better made in square shape
than round ones, the latter being more liable to get choked
up. The suspension of the riddles is effected by four chains
or rods from as many posts. The four chains, or at least two
of them, are provided with set screws, in order to regulate
the position of the riddle. On the back part of the frame
there is a rod connected by a joint, having a tappet on the
other end. The tappet is provided with cams, fixed on the
vertical shaft. Revolving, each cam of the shaft catches the
tappet, pulling the riddle back, which, on being disengaged,
swings to its former position, striking, at the same time,
against blocks fastened to the frame. By the resultant jar,
the small particles fall through the holes; the other part
slides towards the front, and is thrown off by repeated blows.
The percussion will increase the more the chain departs from
a perpendicular line when the riddle is at rest. There is
another double post in the rear, having friction rollers for
the rods of each sieve.
The operation is very simple, and can be applied to wet
stuff as well as dry. The smalls from the hopper or directly
from the crushers must be discharged on the iron-coated part
of the uppermost riddle. The water, spread as much as
possible, must be conveyed upon the sieve, generally only on
the first one; but if the ore be too muddy, water must be
introduced also on the lower sieves. The use of water in
the hopper is less effective, and more of it is required. The
sized smalls are discharged into compartments.
In this, as well as in all other sizing machines, it is of great
advantage if the smalls are freed of mud beforehand in some
way; for instance, by treatment in sluices, drums, etc. It is
sometimes impossible to obtain clean smalls by one operation,
especially if they are coated with tough clay.
A. The Jarring Riddle.--These sizers have a different
construction. Two riddles, sufficiently inclined, each rest-
ing with the lower end on a cross-beam, and striking the
same when dropped after a lift by chains or rods fastened
INTRODUCTION.
39
to the lower end. The upper part is movable on an axis.
The riddles, being lifted from five to eight inches, fall back
on the support, receiving from forty to fifty lifts per minute.
Water is conveyed above the upper riddle on the smalls.
through a launder having holes at the bottom. The riddle,
(eight feet long and fifteen inches wide) contains two sieves
of different fineness, one placed above the other, forming a
double bottom, each having a separate discharge. Below
the second finer sieve is a bottom with an opening towards
the end, through which the finest stuff falls on the second
riddle, (ten feet long, twelve inches wide) the discharge end
of which is opposite that of the upper one. It contains
also, like the upper, two sieves.
The smalls from between the two sieves of the lower
riddle are discharged into a separate compartment. The
finest from the last sieve falls into another place with an
inclined bottom. The smalls discharged on a platform from
the first and second sieve of the upper riddle, are subjected
to picking, wherein six classes are obtained.
1. Smelting ore, which consists mostly of solid galena. 2.
Ore for cobbing, consisting also mostly of galena, but with
adhering rock. 3. Stuff impregnated with large particles of
galena. It is delivered to coarse crushing. 4. Stuff with
finely impregnated galena, for stamping and concentration.
5. Very poor ore; and 6. Refuse rock.
The described apparatus sizes about 265 cubic feet of
smalls per day, but requires a large amount of power and
water.
The riddles with horizontal motion, and the swing riddles,
are preferable to those with a perpendicular one, inasmuch
as the particles of rock with a vertical blow choke the holes
of the sieve with more force, like a wedge, and thus give
also a less favorable result in regard to productive effect.
All riddle contrivances can be used for dry as well as for
wet ore; but with water the work goes on more rapidly, and
yields a cleaner stuff, and dusting is prevented. The best
way of feeding the riddles is by means of hoppers, or self-
feeders.
40
INTRODUCTION.
In some places an arrangement is used in which the sieves
are not placed above each other, but in a row, one before the
other. Consequently the first one must be the finest, and the
coarsest part of the smalls will then roll over all of them.
The last sieve is the coarsest; and the stuff passing over it
is the smallest part of the original charge. The most proper
arrangement is that in which the first sieve contains the
widest openings, so that the finest smalls will reach the finest
sieve by degrees.
According to different sizes, the inclination and percussion
of the respective riddles ought to be different. It is, there-
fore, advisable to construct the apparatus so as to have the
riddles independent of each other in regard to motion and
inclination. The less inclined, the slower the advance of
smalls, consequently a more thorough sifting and cleaning
takes place, but also proportionately a smaller yield of sepa-
rated product.
The size of holes ranges between one inch and one-fifteenth
of an inch in diameter.
The length of the sieves from three to seven feet.
The inclination varies from one to five inches per foot.
The speed from thirty to sixty-eight strokes per minute;
sometimes up to two hundred.
The quantity of the water is also different according to
the nature of the smalls and the size of apparatus. It ranges
from three to sixteen cubic feet per minute. The sieves will
last from two to twelve weeks, according to their arrange-
ment and quality.
Riddles requiring from three to four horse-power are the
heaviest. If properly arranged, a well constructed machine
can size about two hundred and fifty cubic feet per hour.
INTRODUCTION.
41
*
SEC. 12.
The Trommel or Drum.
The Trommel is a sizing and washing apparatus, of a
cylindrical shape. This sizing contrivance is superior to the
preceding ones, which have been already replaced in many
mines by trommels. They are differently constructed, and
used for two purposes, either for cleansing and washing of
the smalls only, or for sizing purposes; but generally for
both combined. The trommels revolve on horizontal or
inclined shafts. If the trommel is used for the cleansing of
ore mixed with clay as a preparation for subsequent sizing,
it is often fitted inside with spikes, (spear trommel) for the
purpose of breaking up the lumps. The spikes are set
either in lines parallel with the shaft, or in a spiral way.
Generally the washing trommels are perforated; sometimes,
however, not. They are made of boiler iron, or of cast-iron,
and are generally connected with the sizing trommels. The
sizing drums are constructed on the same principle, but com-
posed of different sieves or several trommels, each of one
hole size, and are arranged either on one shaft, or one below
the other. Both the washing and sizing trommels move
sometimes with the lower portion of the sieves in boxes or
compartments filled with water, so that there is a permanent
depth of several inches of water inside the trommel. Often
the water rises nearly to the shaft.
Trommels differ in shape, some having a cylindrical, some
a prismatic, and others a conical form. The conical drum
has the advantage of an inclined sifting surface with a level
position of the shaft. In order to effect a forward motion of
the material in a cylindrical or prismatic trommel with a hori-
zontal position, the inside is fitted with a spiral partition, or
there are compartments, formed by rings fixed perpendicular
to the shaft. But as the smalls would always remain in such
*Supplement to Ure's Dictionary, 1863, page 844.
4
42
INTRODUCTION.
compartments, the rings must be open in one place. From
this opening, a cross-plate, in an oblique direction, joins the
other ring, shutting up the space, and forcing thus the smalls
to enter the next compartment, and so on. The construction
of the spiral partition and its maintenance is expensive, and
for this reason conical trommels are preferable.
A. The Cylindric Trommel is the simplest of all drums.
On a shaft there are either iron bars put together closer and
wider apart in different grades, or there are iron plates, per-
forated with holes of different sizes, so arranged that the
finest sieve is at the head or feeding side. On the shaft are
fixed several hubs with arms, to the end of which are
screwed iron hoops, or rings, corresponding in number to the
sizing sieves required. The rivets are not placed close
together, as the plates have to be replaced when worn.
The shaft and the trommel must be laid so much inclined
as to allow the stuff to roll towards the other end, if there is
no spiral arrangement inside. The upper end of the drum,
where the smalls are charged, is usually provided with a
conical collar, in order to prevent the stuff from falling out.
The feeding is managed by means of a spout of sheet-iron
introduced below the shaft, or from above over the shaft.
At the discharge end of the trommel is also a funnel-shaped
collar, widening outside.
Bars, in place of punched plates, are used, principally for
cleansing purposes, or for an auxiliary sorting of coarse
smalls. The sizing trommels are made of sheet-iron,-some-
times also of zinc-, copper- or steel-plates. Copper is gen-
erally used for finer sieves. The riveting of thick plates
with wide holes is not required on the longitudinal joints;
but the rim of one must overlap the other, the lap being in
the proper direction, so as not to interfere with the rolling
of the smalls.
For the washing of smalls, the cylindrical and conical trom-
mels are the most suitable. One inch fall to the foot is suffici-
ent in most cases; but if there is a great deal of clay and mud
INTRODUCTION.
43
1
with the ore, requiring more time to dissolve, less inclination
is given to the drums. They are generally nine feet long,
and from four to five feet in diameter. Sometimes the
nature of the stuff requires cylinders from twelve to fifteen
feet long. During the operation, the trommel revolves partly
under water, or both ends are closed with collars, so that the
water is kept inside several inches high continually, and in
this case the discharge is effected by little elevating boxes,
fixed on the inside periphery of the lower end.
These washing cylinders revolve about ten times per min-
ute. Too fast or too slow causes an unfavorable result. The
charge should reach the lower end after about twelve revolu-
tions. For washing purposes alone, the trommel is not per-
forated, and is usually constructed of staves one and a half to
two inches thick, tied by six iron hoops. The wooden ver-
tical collar inside, at the upper smaller end (if the drum is
conical), is six inches high ;-at the lower, or discharge end,
twelve inches.
The inside of the cylinder is lined with staves one inch
thick, fastened by wooden pins to the mantle. Wooden lin-
ing is preferred to iron, it being cheaper and easier replaced.
These trommels are connected with the shaft by iron arms;
but more frequently there is no shaft inside, the trommel
revolving on friction wheels on the outside periphery.
Water is introduced by an iron pipe. Two to four cubic
feet of water are consumed per minute.
A simple cylindrical trommel is represented in Fig. 10,
Table VI. The shaft, a, is two inches in diameter, and upon
it two armed hubs, b, are fastened. The four arms of each
hub are connected by a flat ring, c, two and a half inches
wide and one-half to three-fourths of an inch thick. The
inner diameter of the ring corresponds with the size of the
trommel. To each ring on each side are screwed four
wooden gaunts, d, on the inner side of which the sieves,
already bent in a cylindric shape, are screwed or nailed.
The long sides of the sieve-plates are overlapped one-half to
three-fourths of an inch, and not riveted at all, or only in the
middle. Fig. 11 shows the hub with the gaunts, d.
44
INTRODUCTION.
Both ends of the cylinder, e, are made of sheet-iron, six
inches wide, screwed to the gaunts in the same way as the
sieves. At the upper or charge end is a vertical ring, i, by
which the smalls are prevented from falling back. Either
the sifting is performed dry, or the lower part of the trom-
mel is a few inches under water. The stuff to be sifted is
introduced through the trough, k, and slides gradually on the
inclined sieve. The smaller grains fall through the sieve-
holes into the compartment, l; the larger smalls are dis-
charged into m.
The inclination of such trommels is not below three and
not above five degrees. Their diameter is from two to three
feet, although a larger diameter is more favorable, but also
more expensive. The length is not less than two feet.
If, as is generally the case, several grain sizes are required,
it is easily accomplished by additional sieves of larger holes
on the downwards prolonged shaft, the space below the
sieves being divided into compartments correspondingly with
the number and size of the sieves. The disadvantage of
this arrangement lies in placing the finest sieve at the head,
where it is exposed to the hardest wear. A better arrange-
ment of sizing trommels, e, e', e', Fig. 9, Tab. VI, is the
reverse, where the finest sieve is the last; but in this case
there are as many shafts as there are different sieves.
B. The Prismatic Trommel differs from the cylindrical
only in its six-sided form. It is generally made of cast-iron
plates, and used only for the coarsest smalls. The holes are
either square or round, the narrower opening on the inside.
The trommel consists of six plates on the circumference,
bolted to collars, which are connected with the shafts by
arms, and with each other by longitudinal ribs. There are
also other constructions without ribs. The smalls roll at
intervals, resting always on one of the six plates, till it rises,
causing them to roll over.
At the Oberhartz mines, there is a prismatic trommel in
connection with four sizing drums, Fig. 9, Tab. VI. The
INTRODUCTION.
45
are
trommel, a, is forty inches in diameter. The shaft has an
inclination of half an inch to the foot towards the picking
table, g. The drum consists of four rows of perforated cast-
iron plates. The holes of the first three, a', a", a'",
three-fourths of an inch; those of the last plates, b, one and
one-fourth inches in diameter. Each plate is eighteen inches
long, making thus a sifting length of six feet. The lower
half of the trommel is covered by a trough, c, having the
same inclination, and receiving the smalls which fall through
the sieve. Where the two sizes join at c', there is a parti-
tion directing the finer part through the conduit, d, into the
first cylinder, e. The coarser smalls from b, fall into a sepa-
rate place,f. The shafts of the four trommels, e, e', e", e'", are
provided with cog-wheels, transmitting the motion from one
to the other. h' is the pulley. Each trommel is five feet
long, eighteen inches in diameter, and inclined three-eighths
of an inch to the foot towards the compartments i, "", into
which the smalls are discharged from each trommel.
The launders, l, l', beneath the cylinders have a reverse
inclination of one-half of an inch to the foot. The lower ends,
grains in them
m, m, are curved, and so inclined that the
are conveyed into the next lower sieves.
The meshes of the first trommel, e, are five-eighths of an
inch wide; of the next, e', three-eighths; of e", three-six-
teenths; and of the last, e'", one-twenty-fourth of an inch
wide. In order to prevent choking of the sieves, there are
horizontal water pipes, n, n', through which streams of water
all along the trommels are forced upon the sieves by a press-
ure of several feet height.
The trommel, c, having its own pulley, makes from sixteen
to eighteen revolutions per minute, the sizing trommels from
fourteen to sixteen. The smalls are charged continually by
means of a hopper, as indicated by dotted lines, p. What is
coarser than the sieve, b, falls over the slide, x, on the pick-
ing table, g, which is perforated, the holes being one and a
quarter inch each side. That which falls through a is carried
into the sizing cylinders by aid of water from the pipe, q.
46
INTRODUCTION.
This apparatus gives eight different sizes of smalls, and is
attended by two men. Of middling smalls, the apparatus
can size about seven hundred cubic feet in twelve hours. It
requires thirty-five cubic feet of water per minute.
C. The Conical Trommel.-This kind of trommel, having
at one end a larger diameter than at the other, allows the ore
to advance towards the wider end, when its shaft is put in a
horizontal position. A conical trommel apparatus (employed
in Hungary) has the following arrangement: On a horizon-
tal shaft are two trommels firmly fastened. The first and
coarser one is surrounded by a wooden or iron mantle, leav-
ing sufficient space for what falls through the sieve. The
sınaller diameter of the mantle is five feet five inches; the
larger, six feet nine inches. Its length is ten feet. Both, the
mantle and the trommel are provided at the large end with
elevating boxes, of which the mantle contains twenty in
number. The second trommel, furnished with a finer sieve, is
about five feet long, the two diameters being the same as
those of the sieve in the mantle. The smalls fall through a
hopper into the first trommel at its smaller end, aided by a
stream of water. The stuff rolls on the sieve and the mantle
towards the larger diameter, where it is taken up by the ele-
vators and discharged when at the highest point of the
circle. The coarsest part, from inside the sieve, when ele-
vated, falls on an inclined launder and rolls on a platform.
The finer part elevated by the shovels of the mantle (which
is twelve inches longer than the trommel) is conveyed by a
trough into the second trommel on the same shaft.
Four classes result from the apparatus described. 1. The
coarser part discharged by the first trommel, delivered to
picking and cobbing. 2. The middle sort from the mantle
spout, concentrated on percussion tables. 3. The fine stuff
from the second trommel, also concentrated on percussion
tables; and 4. The finest part, which fell through the second
trommel, concentrated on rotating buddles.
In twelve hours' time, with two men, the apparatus sizes
over two thousand cubic feet of smalls.
INTRODUCTION.
47
D. A combination of a conical and cylindric trommel is
represented by Fig. 1, Tab. I. This apparatus consists of
two parts. On the shaft, a, is a trommel, b, principally for
washing and freeing the smalls from slime and the fine por-
tions. The shaft is moved by a chain on the chain-wheel, c,
with a speed of from eighteen to twenty revolutions per
minute. The trommel consists of a conical collar, b', for the
reception of smalls through a spout, then of the conical
drum, b, made of boiler iron, fitted inside with a spiral parti-
tion, containing spikes, as represented in Fig. 2. The heads
of the spikes on the outside of the drum, b, indicate the
spiral partition. The spikes are for the purpose of dividing
the smalls.
The cone, b, is five feet long. The diameter of the larger
base is four feet nine inches; of the smaller, two feet ten
inches. The spiral partition, Fig. 2, h, h, projects inward six
inches from the drum mantle, e. The spike, l, projects four
and a half inches from the flange, h. After the cone, follows
the cylinder, f, of two feet six inches in diameter, made of
perforated sheet-iron, with one-eighth inch holes. The next
cylinder, g, consists of iron bars, with spaces of half an inch
between them. This part is two feet long. The smalls
introduced into the trommel with a sufficient supply of water
are conveyed by the spiral partition to the sieve,ƒ. Through
this sieve the slime and finest sand fall into the trough, k,
from which they pass to a sizing trommel of three different
sieves, with respectively 1-32, 2-32 and 4-32 inch holes. The
residue from the bar trommel, g, falls on the inclined trough,
t', and from these upon the picking table. That which falls
through, passes over the inclined table, t, to the sifting and
elevating wheel, m. This wheel is eight feet in diameter.
Its periphery is formed by perforated iron plates, with one-
sixteenth inch holes, and is washed by a stream of water from
the outside. This is done also with the sieve, f, to prevent
choking. That which falls through the perforated elevating
wheel is carried through a spout beneath to another trom-
mel. The wheel has only two elevating shovels, so that each
48
INTRODUCTION.
revolution discharges twice. The material falls upon an
inclined plane, over which it passes to a sizing trommel.
This trommel is five feet long, being composed of five dif
ferent sieves, with holes respectively of four-sixteenths, five-
sixteenths, one-half, five-eighths, and three-fourths of an inch
diameter. Between each two sieves there is a partition open
in one place, where there is a shovel, by which a part of the
smalls is directed at each revolution into the next partition,
and so on to the last one. By this arrangement the smalls.
revolve, or rather the trommel revolves, under the sliding
smalls several times in each partition before they come into
the reach of the shovels. That which falls through, drops
into the respective outside compartments. This apparatus
sizes 980 cubic feet of stuff in ten hours, using 7,938 cubic
feet of water in the same time.
E.
The Elevating and Sifting Wheel. This contrivance
for sifting and at the same time elevating the refuse, can be
considered as a trommel of large diameter and very short
length. This apparatus sizes the ore rapidly into three or
four different classes, with continual charges directly from a
hopper, or in connection with rollers or breakers. It is, how-
ever, more suitable for coarse than fine stuff. Sticky, clayey
rubbish must be excluded. The finest sieve ought not to
have more than twelve holes to the running inch. The finest
sieve is on the periphery of the wheel. Several inches dis-
tant inside is the next coarser; and the coarsest is the last
or innermost of the concentric sieves. All the material to
be sized is conveyed into the central opening of the wheel
on the first and coarsest sieve. The stuff rolls upon the
rotating sieve, and that which is fine enough will pass through
the holes into the next compartment with the finer sieve,
and so on to the outer and finest. Each circle of sieves has
one stop-bucket, or partition, which, at each revolution, takes
up the coarser remnant which always rolls at the lowest
point, and discharges it, when elevated to the highest point,
through a short spout attached to each stop-bucket.
INTRODUCTION.
49
The stuff must be either very dry, or if wet, it requires a
stream of water to assist the sifting, and it is best, in this
case, to have the lower part of the wheel in standing water,
especially if the stuff is not coarse. The wheels are from six
to fifteen feet in diameter. For clear stuff, the arrangement
can be made with double openings and stop-buckets, so that
two discharges are effected at each revolution.
Generally these wheels are employed for washing and pre-
paratory sizing of smalls from the mine with two coarse
sieves, and are preferred where the elevation of the stuff is
required at the same time.
Motion is generally imparted to the trommels by pullies or
gear fitted to the shaft or the periphery of the drum, or
they are made to run on friction gear, in which case no shaft
is required, and the feeding is more simple. In arranging a
sifting apparatus, care should be taken to separate first the
coarsest part, and at the same time to get rid of the slime.
The choking is best prevented by using water under some
pressure upon the outside of the sieve; also by wooden
knockers falling on the sieve at intervals. Trommels of
small sizes, from one and a half to two feet diameter, are not
much in use, unless directly in connection with a concentrat-
ing table. The length of the first, which is generally a
washing drum, depends on the nature if the smalls. If there
is much clayey matter with them, the trommel must be
longer, from six to ten feet. The sizing trommels are from
five to seven feet long. The diameter ranges from three to
six feet; that of the washing drums from five to seven feet.
The speed of the surface of the sieve is one to two and a
half feet per second. A well arranged apparatus, consisting
of one separating and four or five sizing trommels, ought to
size about twenty-five tons of smalls in twelve hours.
50
INTRODUCTION.
ว
SEC. 13.
Sizes of Grains for Jigging.
The result of concentration depends on proper sizing, and
this again on the right proportion of sizing-holes of the dif-
ferent sizing systems. The following sizes adopted by Rit-
tinger show a systematical progression, and also the equal
fall of different sized grains in water ($35, a).
In this respect, the sorts of one class correspond with those
of the next; for instance, a galena grain of No. 2 which
falls through the holes 8 or 16 is equal in falling—i. e., has
the same speed in water as a quartz grain which falls through
the holes 32 or 64 of the next higher class, No. 1.
For the sizes of the holes (equal to the diameter) one mili-
meter is taken as the unit of measure. The progression of
the diameter is a geometric one, as the grains of the next
grade should have a definite size, which should be always
the same multiple of the next preceding one. The following
progressions, therefore, are obtained :
•
For the volumes.
1, 8, 64, 512, 4,096 cub. milim.
For the hole-diameter. .1, 2, 4, 8, 16
•
milim.
But, as the eight-fold gradation of volumes is too great, it
appears necessary to extend the preceding sizes in both
directions, and insert between each of the above grades a
middle grade, which progresses according to a similar law.
The sizes thus obtained are divided into four classes, each
having four grades:
Diameter in Milim. In inches (very near).
Inches.
Milim.
64
= 2.51
coarse.
4
= 0.160
No. 1.
(Stufen.)
45.2
1.79
32
1.26
middle coarse.
middle fine.
No. 3.
(Gries.)
2.8
= 0.109
2
0.078
22.6
= 0.89
fine.
1.4
0.055
16
0.64
coarse.
1
0.040
No. 2.
(Graupen.)
11.3
0.45 middle coarse.
No. 4.
0.71
0.0282
8
0.319 middle fine.
(Mehl.)
0.50
= 0.0200
5.6 = 0.220 fine.
0.35 0.0137
(Staub.) 0.25 mil. = 0.010 inch.
INTRODUCTION.
51
Sand which falls through the last sieve of 0.01 inch holes,
cannot be advantageously sorted further by means of sieves.
The first class commences with smalls of two and a half
inches, as pieces of that size are already objects of mechani-
cal treatment by machines. Only the finest sieves-those of
No. 4; seldom of No. 3-are of wire cloth. Copper sheet
screens are too expensive; their durability is not in propor-
tion to their cost. Sheet-iron is the most suitable. For the
largest holes, also cast-iron.
The holes must be punched as closely as possible, without
weakening the sieve. The most proper arrangement is that in
which around one hole six others are grouped, the centers of
all being equally distant. The space between the holes takes
half of the hole size; but with the finer sieves, this space is
equal to the diameter of the hole.
The thickness of the sheet must be in a certain propor-
tion with the size of holes.
The four sorts of No. 1 are from 0.12 to 0.16 of an inch thick.
เ
"(
"C
"
(6
2
((
(C
1.078 0.10
"
(C
3
(C
((
((
เ
4
#
0.04 0.07
0.02 " 0.028 "
(.
For sizing purposes, the sieves are employed in two ways.
Either the coarsest sieve commences and the finest finishes
the sizing, or the work is begun with the finest and ended
with the coarsest. The first method is far preferable,
because the whole sifting system will stand the wear much
longer.
Both ways, however, can be combined, employing two sys-
tems of sieves. First, a system of sieves with about four
decreasing sizes of holes, each size being that of the largest
holes of one of the above four classes, would give four sorts
of stuff in which mixed grains appear. Each group is then
transferred to a sifting apparatus with increasing sizes of
holes. This arrangement allows a simplification of the sift-
ing apparatus.
་
II. REDUCTION.
SEC. 14.
Reduction of Ores to a Proper Size.
The concentration of ore particles in a mass, and the rejec-
tion of the worthless rock by means of water on proper
machines, requires a definite size of ore particles, to which it
must be broken, crushed, stamped, or ground, according to
the nature of the ore, which must also determine the mode
of concentration, and consequently the size of grains. The
size and shape of the ore particles are two important consid-
erations, influencing the separation of ore and gangue to a
considerable extent. ($35, a, b.) The dry dressing is more
simple, requiring an empirical acquaintance with the ore and
a strict performance of hand separation according to local
rules. A loss of valuable ore is of little danger, inasmuch as
if accidentally a rich piece happens to be thrown on the
wrong heap, it will be subjected to the concentration process.
A mistake in the way of concentration, however, is, in gen-
eral, a dead loss; consequently a systematic calculation must
be made beforehand as to the suitable plan of concentration,
considering with caution all particulars in connection with
the nature of the ore, gangue and rock. Concentration.
deserves so much the more attention, as in most instances the
largest part of the vein rock is unfit for any process before
concentration. Another reason is the fact that the ore of
54
REDUCTION.
many a mine grows poorer with the increasing depth, from
which cause all the ore taken from the mine may appear as
concentrating ore. In California and Nevada, the silver and
gold ores, to a great extent, are treated without roasting, in
pans. The loss suffered on this occasion is found in the tail-
ings, which, for the purpose of concentration, are very
important, because of their immense quantity, being at the
same time free of mining, crushing and hauling expenses.
Concentration cannot be effected without a loss of from
fifteen to thirty per cent., especially in the case of silver
ores, and it is considered the highest degree of perfection if
not more than fifteen per cent. is lost. If ore is finely dis-
seminated in the gangue, requiring very fine crushing, the
total loss may amount to fifty or sixty per cent., and under
otherwise unfavorable circumstances (for instance, besides.
the fine condition of a brittle ore, the presence of clay, heavy
spar, etc.) the loss may rise to ninety per cent., rendering
concentration impossible. But the loss depends very much
on the process of reducing the ore to powder; and it is
therefore advisable to become acquainted with the various
methods of reduction, and their choice of adaptation to the
nature of the ore.
The reduction gives a mingled mass. consisting of coarse
grains and all inferior grades to the finest dust. When sifted
through different sieves, classes of sized ore are obtained,
differing in quantity. A hard, tough quartz will give, in pro-
portion, much less dust than decomposed gangue; but even
the same mineral yields variable proportions of certain
classes, according to the mode of crushing adopted. Experi-
ence has shown that crushing under rollers and breakers pro-
duces a great deal less dust than under stamps, and this again
a good deal less than the reduction by grinders.
According to Rittinger, crushed ore from rollers gives
Coarse grains.
Sand....
Flour and dust.
•
70
per
cent.
.20
((
(C
.10
"
REDUCTION.
55
And wet crushing under stamps, through 5-32 inch holes,
Sand..
Flour.
Dust...
32 per cent.
32
.36
(C
The grains will be the more equal in size the less differ-
ence there is in the size of sieve holes; but a considerable
difference in shape will be found always in each class.
($35, b.)
Reduction is generally effected by heavy stamps, rock
breakers, common stamps, rollers and grinders.
SEC. 15.
Breaking Under Heavy Stamps.
The ore, for the purpose of selecting or dressing, is reduced
to a convenient size by large hand or sledge hammers, within
or outside the mine, as before stated; but it often occurs
that the ore, on account of a uniform distribution of valuable
parts, is considered rich enough to be worked without dress-
ing, or the distribution is of such a nature that a dry dressing
would appear useless, and it is shipped directly to the mills
in inconveniently large blocks of from one to three cubic
feet. The breaking of such rock by hand hammers requires
many hands. Burning in heaps or kilns, where fuel is not
too expensive, makes the quartz brittle and facilitates the
reduction by hammers to a great extent. But in many cases
the price of fuel is high, or the chemical influence of fire
upon the ore may be objectionable. Rock-breakers with
jaws are not suitable for too large rocks. They are not made
to break advantageously pieces larger than a definite size—
say ten inches. All rock above this size is broken either by
sledge hammers or by heavy stamps. In the construction
of heavy stamps, everything is so similar to the ordinary
stamps ($17) that a special description is unnecessary. The
56
REDUCTION.
principal difference consists in the size. There is generally
only one stamp, with an independent frame. The breaking
is, as a matter of course, always performed dry. The stem,
or lifter, is made of wrought iron, four and a half inches.
diameter, and about seventeen feet long. When armed-that
is, furnished with head or socket, shoe and tappet-the stamp
weighs from fourteen hundred to fifteen hundred pounds.
The shaft, six inches diameter, has a single armed cam, by
which the stamp is lifted from thirteen to fifteen times per
minute, thirty inches high. The anvil or die, about thirty-
two inches above the floor, has a collar a few inches below
the die-face, serving as a support for grates, to which differ-
ent shapes are given, generally curved. In a preparatory
crusher, the ore should not be broken smaller than a man's
fist.
Many of these stamps are used in California and Nevada;
but the introduction of improved stone-breakers makes the
application of heavy stamps superfluous. They require a
great deal of attention and care while in operation, especially
if, on account of grates, shoveling is required. Besides it
proves always a defective arrangement at the mine if large
pieces of ore are shipped to the mills, unless no doubt can be
entertained as to uniformity of the whole mass.
SEC. 16.
Reduction by Rock-Breakers.
There is a great variety of stone-breakers in use. In all
of them, the main part consists in two substantial jaws, of
which one or both are movable. The position of the jaws
varies. They may be, one or both of them, vertical or
inclined. Sometimes they are curved. Also, the motion is
applied in various ways to the jaws, horizontally or verti
cally, generally at the lower part, where the broken stuff is
discharged. The jaws are faced with wearing plates of
REDUCTION.
57
white iron, chilled and hardened, provided with teeth, smooth
or corrugated. A description of a couple of breakers will
give an idea of the general construction.
Well constructed breakers are very efficient, and produce
a suitable stuff for concentration to a certain size with the
least proportion of dust. In this respect they are superior to
rollers. For this reason also, breakers are preferable to
stamps in reducing ore to a small size for smelting purposes
in blast furnaces. Some mills are trying to dispense with
stamps, employing breakers, which crush the ore to one-
fourth of an inch, and smaller, and reducing this further in
pans. There are breakers which, it is claimed, reduce the ore
directly to fine powder. Success will be found more likely
in using different sizes of breakers, or in connection with
rollers. Two sizes of breakers may produce a stuff suitable
for immediate grinding and amalgamating in pans.
For the reduction of small quantities of ore, for instance
of ten or fifty pounds, for prospecting purposes and amalga-
mation on a small scale, breakers offer a very convenient
method of reduction by hand power.
A serious objection to substituting breakers for stamps is
found in the difficulty in pulverizing ore which is wet or
damp, or intermixed with clay or mud. There are, in real-
ity, few mines where a proper material could be extracted
for the breakers, unless picked or dried.
A. Hanscom's Crusher.-This breaker consists of a mova-
ble jaw, on which is placed a die or face made of white iron,
and so fitted as to be easily replaced when worn. The frame
is made of cast-iron, of sufficient strength to withstand the
strain caused by the pressure between the two dies. The
other die corresponding with the first is fitted in the frame,
immovable, except when required to be replaced.
The action of the machine is as follows: When the fly-
wheel is revolved, the lower shaft is vibrated with links on
the upper shaft as a center, and the bottom end of two tog
gles is carried with the lower shaft, on which it sits; but the
5
58
REDUCTION.
top working on the knuckle can only move in a vertical direc-
tion, so that, as the bottom is carried away from a line which
passes through the center of the links, toggle, and the lower
shaft, the top of the toggle will begin to lower; consequently
the jaw which is supported by it will follow by its own
gravity.
This downward movement of the jaw will continue until
the extent of the throw of the crank is reached, when the
movement of the fly-wheel and shaft causes the bottom of the
toggle and lower shaft to return to its first position and the
jaw has again risen to its first position. It will be noticed
that this is the point at which the greatest force is exerted in
lifting upon the jaw. If now the crank-pin has sufficient
throw to carry the bottom of the toggle to the opposite side
of the vertical line through its center, the same action will
take place as before, and the connecting-rod may be of such
a length that the lower shaft will be moved equal distances
each side of the center, and two up and down movements can
be given with one revolution of the crank wheel, which is
considered to be of great advantage, as by this arrangement
double the number of movements may be given to the mova-
ble jaw that could if one revolution of the fly-wheel produced
only one movement of the jaws.
In breaking large pieces, the faces require to have but
little approach to one another; but as the pieces become
somewhat smaller, more approach is required, but not so
much power. When the fragments have reached the required
size, then the faces require to be nearly parallel and perpen-
dicular, so that the point of exit shall be uniform.
B. Blake's Quartz Breaker.-This machine is well known
and extensively in use. Fig. 3, Tab. I, shows Blake's breaker.
It is a vertical section. a, a, is a heavy frame, cast in one
piece, with feet to stand upon the floor or on timbers. It
receives and supports all the other parts. b is the fly-wheel,
one on each side, the shaft of which is formed into a crank.
c is a pulley on the same shaft. d is a connecting-rod, which
REDUCTION.
59
connects the crank, e, with the lever, f. This lever has its
fulcrum on the frame, g. A vertical piece, h, the front view
of which is shown in Fig. 5, stands upon the lever, against
the top of which piece the toggles, i, i, have their bearings,
forming an elbow or toggle joint. k, is the fixed jaw, against
which the stones are crushed. It is held back to its place
by keys, l, that fit in recesses in the interior of the frame on
each side. m, is the movable jaw, faced with a corrugated
die, m'. The jaw is supported by a round bar of irou, n,
which passes freely through it, and forms the pivot upon
which it vibrates. o, is a spring of India-rubber, which is
compressed by the forward movement of the jaw and aids its
return. Fig. 4 is the lever viewed from above. Fig. 6 is
a top view of the die, k, which is corrugated on one or
both sides. In the latter case it is turned after one side
is worn.
p, is a screw, by which the wedge, r, can be
screwed up in order to bring the jaw, m, nearer to k, thus
effecting a finer crushing. The crank, e, revolves from one
hundred and fifty to two hundred times per minute. The
distance between the jaws may be raised to the extent of
five-eighths of an inch by the screw, p. Further variations
are made by substituting for the toggles, i, i, or either of
them, longer or shorter ones.
These machines are made of different sizes,* which are des-
ignated by the size of the opening. For instance, if the
width of the jaw be ten inches, and the distance between
them at the top five inches, the size is called 10x5, etc. A
machine of 20x7 requires eleven horse-power, and weighs
eighteen thousand pounds total, the frame itself weighing six
thousand six hundred pounds.
The oil boxes of the shaft and connecting-rod should be
kept always covered while the machine is at work. The
spring must be slacked whenever the wedge, r, is to be raised
or lowered. It is also necessary to stop the machine every
hour, and apply oil freely to all the working joints. The
ends of the toggles may be oiled without stopping the
*Union Foundry, San Francisco.
60
REDUCTION.
#
machine, and as they work under immense pressure, and are
not so well situated to retain the oil as the other joints, they
should be oiled every half hour. There are a great many
new contrivances of this kind in operation, giving the best
satisfaction.
SEC. 17.
Reduction by Stamps.
The crushing of ores under stamps to a suitable size for
concentration by jiggers, was formerly done in the dry way.
This method, however, is now mostly abandoned, except for
metallurgical purposes. In wet crushing, not only is the
inconvenience of dust avoided, but the separation of stuff
according to density, and especially to size, is effected at the
same time to some degree, and without expense. The reduc-
tion of ore to sand suitable for concentration, with reference
to the nature of the ore, has been tried by various contriv-
ances, but none could answer the purpose as well as the
stamps. Also in England, where crushing under rolling mills
has been brought to high perfection, the fine reduction to
sand for the purpose of concentration is still in preference
done by stamps.
The mode of constructing a stamp work varies much,
especially as to the foundation frame. Quality and quantity
of timber, local circumstances, and the nature of the ground,
will decide the modifications; but in main points, all the
mills agree. The principle of a stamp work is that of a
hand mortar and pestle. Generally there are four to five
pestles or stamps employed to crush in one mortar. Six or
three stamps are less in use. In California, one mortar with
its stamps is called a "battery." In other places, this term
is given to the whole number of stamps in a mill (“a battery
of fifty or sixty heads.")
The frame of a battery is made of wood or iron. Wooden
frame-works are preferable to iron ones, on account of firm-
REDUCTION.
61
ness and elasticity at the same time; but local circumstances,
-for instance, want of timber-recommend often an iron
frame. The foundation is a very important part. The dura-
bility of a battery depends much upon a proper foundation.
For that reason much attention is paid to securing substan-
tial timber and arranging it properly. But also masonry, in
place of timber, is used. In Europe, stone foundations are
preferred for iron batteries.
A battery frame consists of a horizontal or vertical mortar
block, the uprights or frame posts, and the cross pieces to
which the stamp guides are attached. Vertical mortar
blocks are more in use than horizontal ones, the latter being
more suitable in unsafe, marshy ground.
A. The Foundation.-In marshy or unreliable ground
there is no use in a deep excavation; but it requires a broad
base for the frame foundation, as shown in Figs. 7 and 8,
Tab. I.
The surface of the ground must be removed from one to
three feet deep, and as wide and long as the condition of the
ground and number of batteries may require. Figs. 7 and 8
represent a foundation with a horizontal mortar block for two
batteries. Fig. 7 is a front, Fig. 8 is a side view. Flooring
underneath the timber with boards is improper, and in case
the bottom should appear unsafe, the lower timbers must be
laid close together. The bottom timbers, a, a, are twelve
inches square and eighteen feet long, laid upon the carefully-
leveled ground for the required distance. Between a, a, in
in the middle, short pieces, c, about two feet long, are laid, to
fill up the space under the double cross-timbers, b′, b'.
There are generally as many beams, a, a, as there are up-
rights, f.
The cross-timbers, b, b, are laid upon a, and over b, a row
of beams, d, corresponding with a, a. The mortar block,
e, finishes the horizontal frame. The mortar blocks are
from twenty to thirty inches square, the ends generally
secured by iron bands. Oak wood is the best material, but
62
REDUCTION.
scarce; therefore pine blocks are more in use. The length,
of course, depends on the number and size of batteries. It
is often preferred to have each battery run separately. This
requires a good deal longer block. Independent batteries.
offer the advantage that the cam shaft can be stopped if
necessary without interfering with other, batteries.
To impart more consistency and firmness to the whole
foundation frame-work, the timbers are bolted together by
the bolts, h. The space between them must be filled and
beaten in with clay, loam, or, still better, with coarse gravel
and stones, as shown by g. Where the ground acquires some-
what more consistency at a depth of four or five feet, the
whole frame is set so much deeper, and in this case short
vertical pieces, as indicated by the dotted lines (i), are fitted
on the mortar block, bolted together lengthwise, as shown by
k, whilst the lower ends are let into the block. The planks,
m', assist in preventing a side motion of the blocks, i.
Horizontal mortar blocks are used advantageously also on
a rocky, hard ground, the excavation of which is difficult and
expensive. In this case less timber is wanted. Such ground
may be considered as an artificial stone block, as represented
by Fig. 9, Tab. I. The mortar block lies on the beams, b, b,
and this again on the bottom pieces, a.
It would contribute much to the steadiness of the frame if
the bottom timbers were anchored with iron rods to the
rock; but in case heavy stamps are to be used, a foundation,
as shown in Figs. 7 and 8, Tab. I, will answer perfectly, if
the space between the timbers is filled with rock.
The usual depth as required for the perpendicular mortar-
blocks is from six to ten feet, sometimes more, especially if it
appears necessary to have the discharge of the mortar higher
than usual above the ground.
Figs. 11 and 12, Tab. I, represent two batteries, five stamps
each. The mortar-blocks, c, c, stand perpendicularly on the
base timber, a. They are fourteen inches by twenty-four ;
two for each battery, bolted together, and to the posts, d.
The space, c', is either stamped in firmly with rock or clay,
REDUCTION.
63
or fitted tightly with timber. Posts and blocks are tied
together by cross-beams, e, e, f, f, and g, g'. The ground
around the foundation frame must be stamped in as hard as
possible, and a proper material used for this purpose, either
rock or a clayey loam.
A different construction of frame and foundation is shown
by Fig. 10, Tab. I. This style is frequently found in the
Reese River mines, Nevada. This mode of framing gives a
considerable steadiness to the whole work, and allows the
omission of the front braces, although they are often applied
as indicated by the line, b. Modern batteries in Europe have
no braces; but although inconvenient, and much in the way,
they are necessary, for the reason that the cam-shaft is here
attached to the upright posts directly, which is not the case.
in Europe. In place of wooden braces, there are also iron
rods frequently in use, or iron and wooden together, as shown
by m, n, Fig. 12, Tab. I. Iron rods have the advantage of
taking up less room, being capable at the same time of being
tightened if necessary; but more steadiness is obtained by
wooden braces.
The posts, d, d, should be of heavy timber, for the sake of
strength imparted to the whole battery. The usual size
ranges between eight to twelve by eighteen to twenty-four
inches. To these uprights are fitted and bolted the cross-
beams, i, i, connecting two or more batteries. As a constitu-
ent part of the battery, the cross-beams, i, serve also as
support of the guides, k, k'. The relative position of both
is therefore definitely depending on the guides. The further
apart are the guides, the less is the friction of the stems in
them. It is sufficient if the stems project from six to eight
inches above the upper guide, leaving between the lower one
and the mortar about twelve inches space. There are some-
times one or two top beams, j, connecting several batteries.
Another plan is shown by Fig. 1, Tab. II. The mortar-
block, a, of which there are from three to four pieces under
each mortar of five stamps, is ten feet long. The uprights,
b, rest on the horizontal floor timber, c, joining and bolted
64
REDUCTION.
together at d. Over the top of the post there is an iron cap.
e, through which and partly through the uprights an iron rod,
f, extends down through the timber, c. g, is a platform, and
h, stamp-hanger.
+
B. Iron Battery Frames are coming more into use in
Europe, principally for want of heavy timber. The con-
struction is similar to the wooden frame, differing, however,
with the different material. The iron batteries in Freiberg,
(Saxony) stand on a stone block, to which the frame is fast-
ened by long bolts. The mortar is divided by an iron cross-
plate into two compartments, each for three stamps. There
are six wooden stems playing between each two uprights.
The frame-work has no braces, but the bearings of the iron.
shaft are not in connection with the frame. Many iron bat-
teries are in use also in England, generally with iron stems
of a square section.
In California and Nevada, the number of iron batteries is.
subordinate, as most mining localities are supplied with the
most magnificent timber. There are two different construc-
tions of iron batteries with rotary stamps. "Howland's rotary
battery," with from six to twelve stamps, placed in a circle.
The bed is six feet in diameter, and the frame ten feet high.
The discharge is not very rapid. The other style is the
straight battery.
1. Fig. 3, Tab. II, represents a Straight Iron Battery,
consisting of four pillars, a, to each battery of four or five
stamps, fastened to the frame, c, by iron rods, b, passing
through the hollow uprights, a. The guide frame, e, and the
bearing, d, are bolted to the projections of the uprights. ƒ,
connects both uprights, and serves also for the reception of
wooden guides, g. The base, i, of the pillar is eight inches
by twelve. The frame is connected with the timber, a and
x', by the tightening rod, h. The mortar, k, is in no connec-
tion with the iron frame. In this respect it differs from the
REDUCTION.
65
2. Bryant's Battery, which has a heavy solid bed-plate, to
which uprights similar to a, Fig. 3, Tab. II, are fitted and
tightly held by an iron rod. On the pillars are flanges, to
which the screws in a wooden frame are screwed or wedged
in the usual way. The balance of the mortar sides is formed
of sheet-iron. These batteries answer also for dry crushing.
In this case it happens very often that the dies, although
provided with two projections, a, Fig. 20, Tab. I, (which, by a
turn, are brought into the dove-tailed space, c, of the bed-
plate, Fig. 21, Tab. I) work back into the recess, b, and come
out while crushing. To avoid this, the dies for dry crushing
have sometimes on the bottom a key seat, d, which corres-
ponds with a similar seat, e, of the bed-plate. A square iron
rod is then driven through the key-way, d, e, and the die is
thus firmly set. A better way to fix the die to the bed-plate
is that introduced by Z. Wheeler, (because each die can be
removed independently of the others) where the die has a
neck, g, which fits into the hole, h, of the bed-plate, project-
ing below so much that an iron wedge, k, will tighten the
die to the bed-plate.
The Freiberg plan, to give a sufficient base to the iron
post, Fig. 8, A, B, Tab. III, seems to be more proper for iron
batteries than hollow pillars with a few square inches base,
which is not equalled by the use of two pillars and iron rods.
The pillar is bolted by long bolts, a, a, to a solid stone block.
c, c, serves for the reception of wooden guides.
3. Wright's Iron Battery, recently invented, (New York)
differs from all other batteries by dispensing with cams.
Each stem is lifted by the direct action of steam, the lifters
being connected with a steam piston, working in its own sep-
arate cylinder for each stamp.
The cylinders are all cast together, with a surrounding ex-
haust steam-jacket and a sole-plate, and are supported on
wrought-iron pillars erected on a bed-plate. All the cylin
ders can be adjusted simultaneously by means of nuts, fitted
to screw-threads on said pillars, for the purpose of adjusting
66
REDUCTION.
the clearance between the pistons and the top and bottom of
the cylinder, and for maintaining a uniform clearance by
lowering the cylinders as the stamps wear away and allow
the pistons to descend lower. Each cylinder has an inde-
pendent valve and automatic valve-gear, so that each piston
and stamp may work independently of all the others.
This battery seems to offer important advantages. As the
lift is effected perpendicularly, no side friction occurs in the
guides, as otherwise is produced by cams; consequently the
guides will last considerably longer, and as the steam acts
above and below the pistons, the force of the downward pres-
sure on the piston increases the crushing power of the stamp.
This fact is especially important in crushing dry, as the free
fall of the stamp has not sufficient force to throw the pulver-
ized ore effectually toward the screens, especially if the ore
is rich in sulphurets.
C. The Mortar.-The bottom on which the ore is thrown
in order to have it reduced by the falling stamps, was origin-
ally stamped quartz or solid stone. In Europe, the artificial
rock bottom is yet in use to a considerable extent. There
are many advantages in favor of this kind of mortar beds.
In the first place, it is not only very cheap, but the required
material of a hard quartzose rock can be obtained every-
where; also the poorer class of ore itself will answer per-
fectly if sufficiently tough and hard. There is no difficulty in
keeping the bottom always at a certain level. On the other
hand, it is just as easy to change it as it may suit. It is also
claimed that the rock bottom yields a more uniform sand,
especially in fine crushing, and if at the same time tough min-
erals occur in the rock, like chloride or sulphuret of silver, or
if there is metallic silver, gold or copper in the ore, which on
an iron bottom would be sooner beaten into scales or leaves,
a very disadvantageous shape for concentration or direct
amalgamation on copper plates or similar arrangements. The
coffer into which the rock is beaten in order to form the bot-
tom, is made either of cast-iron, generally lined inside with
REDUCTION.
67
planks, or it is constructed of stout timber. The rock, of the
usual size, is introduced dry into the box, and the stamps
allowed to play upon it with a slow motion. These rock bot-
toms are of more value in localities remote from iron foun-
dries, where transportation is troubleseme and expensive,
and the ore not very rich.
The iron bottom yields more pulverized stuff in the same
time, and there is hardly a mill found in California or Nevada
having a rock bottom (although it was tried many years ago
in Mariposa county and other places in California). The
cast-iron bottom-plates in Europe are generally four inches
thick, and as long as a battery of three or four stamps
requires; but there are also square bottoms used, about six
inches by six and thirty inches long. After some time, when
the upper side is worn out, showing a cavity under each
stamp, the bottom is then turned, so that another straight
surface forms the crushing bottom. This turning is repeated
until all four sides are used up. Using a bottom-plate, the
trough or mortar is generally made of planks, lined with
wrought-iron plates of from one-fourth to one-half inch thick-
ness.
It is, however, extremely difficult or entirely impossi-
ble to keep a wooden mortar perfectly tight for any length of
time, especially if heavy stamps are in use. For this reason
the cast-iron mortars, as generally introduced in California
and Nevada, both for dry and wet crushing, are superior to
all other arrangements. The only objection is the expense.
A mortar weighs from two thousand four hundred to four
thousand pounds, making, besides its original cost, a consid-
erable freight expense. Considering, however, the expense
and trouble of keeping a common mortar with an iron bed-
plate and wooden sides tight enough to prevent leakage, and
of making many other necessary repairs in the course of
several years, the iron mortar will be found to effect a saving
in money and time.
The only wear which occurs in the mortar is on the sides
near each die, and this can and ought to be prevented by
lining the same with plates half an inch thick and six inches
68
REDUCTION.
wide, which are fastened by bolts to the sides of the mortar,
as is done in some mills. It takes but a few hours to replace
them when worn out, and the mortar will answer for many
years longer. The construction of a mortar is shown in Fig.
3, B, and 4, Tab. II. The mortar consists of one piece; l, is
the feed-trough, widening somewhat downward. At m, the
surface is generally protected by an iron plate against the
falling rock. In case the mortar is made to discharge on both
long sides, the feed is then above the screen, projecting a
little into the mortar, so that no ore may strike and damage
the screen. At n, the opening is usually about three inches
wide, and nearly as long as the mortar itself; shown by the
dotted line, p. The discharge is effected through the opening,
o. The lower rim of this opening is from two to three inches
above the die, r.
On each side there is a rib, s, for the pur-
pose of pressing the screen-frame tight against the mortar,
either by screws, or (as shown in Fig. 1, Tab. II) by a wedge,
0. For the same purpose there are also two or three knobs,
v, on the discharge-plate. For the reception of the dies, r,
there are circular hollows of half an inch depth, which is
sufficient to keep the die in its place, if wet crushing is in use.
When the dies are set in, some sand or tailings is spread all
around, one or two inches deep, then the ore introduced so
that the dies are covered two or three inches. In presence
of water the crushed ore soon packs between the dies.
Another shape of dies for wet crushing is shown in Fig. 22,
Tab. I. They are placed in flat-bottomed mortars, which
seem to be preferable, as the circular hollows for the recep-
tion of dies grow wider by long wear.
Crushing dry, the plain groove is often troublesome; the
crushed stuff works itself beneath the die and displaces it.
To prevent this, the dies have two projections, a a, at the
bottom, as represented in Figs. 20 and 21, Tab. I. When
placed with the knob, a, in the open recess, b, of the bed-
plate, the die is turned about ninety degrees.
The mortar is fastened to the mortar-block by strong bolts,
w. It is very important that the two joining faces of mortar
REDUCTION.
69
1
and block are perfectly level and smooth; for this reason the
bottom, z, of the mortar is planed smooth from outside. Other
mortars are shown in Fig. 12, Tab. I, and Fig. 1, Tab. II.
The Stamps.-A stamp consists of the stem or lifter, the
head or pestle, and the tongue or tappet.
D. The stem or lifter originally was made of oak or pine
wood, square in section. Wooden stems are used almost every-
where in Europe, on account of their cheapness or the facility
of obtaining them. Iron stems are preferable in every
respect. There are square and round ones in use. Their
durability, and the exactness of their fittings, by which they
are kept in good working order for years without repair, ren-
der the iron stems cheaper than the wooden ones. They are
made of wrought iron, square or turned in the lathe.
The round section of the stem is the only one used in
California and Nevada, and there is certainly no other shape
which can answer quite so well. A very important advantage
of the round stems is the revolving lift, whereby the pestle
changes constantly its face towards the feed side, acquiring
thus a most uniform wear, so that a worn shoe often shows
only a disc of one-eighth of an inch thickness on the circum-
ference all round. Another advantage is the facility in fitting
the head, as well as the tappet, on a round stem. Length
and thickness differ. Generally a stem measures from ten to
twelve feet in length, and from two and a half to three
inches in diameter. The end of the lifter which comes in
connection with the head is tapered somewhat. All the rest
is perfectly round and uniform. The flat cut or face against
which the keys of the tappet are wedged, and also the screw
thread by which the tappet is held at the required point, are
no more in use, as the latest construction of the tappet
allows the use of a round smooth surface of the stem, so that
it may be fixed at any required point easily.
E. The Shoe or Pestle.—The wooden stems and the square
iron ones are connected directly with the shoes. The revolv
70
REDUCTION.
ing stems are fitted in heads, or sockets, which receive the
shoes. The shoes are made generally of cast-iron; but there
are also wrought-iron and steel shoes. The form is mostly
square or rectangular, often round; sometimes eight-edged,*
having on the upper end a neck, which fits into a correspond-
ing recess in the wooden stem or in the socket. In some
places the shoes are square, without a neck, in place of which
there is a tapered hollow, into which the wooden stem is
driven, as represented by a, Fig. 14, Tab. II. This way of
fitting the stem into the shoe is convenient; but it requires
accurate work, else the shoe will slip off while stamping.
The neck of the shoes is not always square or round. Some
show an oblong section, the long side being equal with the
width of the shoe. This form of neck weakens the stem,
however, as the cut must go through the whole width of it.
In Cornwall, the iron stems at the lower end are split cross-
ways, the four ends bent outwards, and the shoe cast over it,
or a piece of one or two feet in length is prepared in the
same way, and the stem joined with it at welding heat.
Similar methods are also used in Spain. The best way of
connecting the stem properly with the shoe without trouble
is undoubtedly that practiced in California, Nevada, etc.,
using the rotating stems. For this purpose there is
F. The Socket, or Head, as shown in Fig. 15, A, Tab. I. A
represents the front view, B, the section of 4. a, is a slightly
tapered hole of about seven inches depth. Its upper diam-
eter is nearly equal to the size of the stem, the end of which
to the length of six inches is also tapered. At the bottom of
*In reference to the sectional shape of shoes, a square or rectangular section is
the best, inasmuch as nearly all the room in a mortar is taken up, avoiding thus
dead masses of rock, which occur if round shoes are employed. The agitation of
the water by square shoes is livelier, and more favorable for the discharge. For
these reasons square shoes are more in use than round ones. Compared with the
revolving round shoes, the square ones have the disadvantage of wearing more on
the feed side than on the discharge. Round shoes with revolving stems proved to
be superior to all other shapes tried in California; and for this reason only the
round section is adopted on the Pacific coast.
REDUCTION.
71
the conical hole, with a smooth casting surface, is an oblong
opening through the socket.
This passage, c, serves to drive out the stem by means of a
key if required. The socket is placed upon the die in the
battery; the stem, when fitted in the guides, dropped with the
tapered end into the correspondingly tapered hole, a, of B,
and then a few blows with a hammer are applied at the other
end of the stem. This will produce a sufficient connection
between stem and socket to lift the latter with the stem, and
tighten the connection by a few blows of the stamp. The
other hollow, d, is similar to a, but wider, corresponding with
the size and shape of the neck, e, of the shoe, Fig. 16, Tab. I.
Like c, there is another rectangular hole, f, by means of
which the neck of the shoe when worn out is easily removed.
Both ends of the socket are secured by wrought-iron rings,
g, which are driven on tight when red hot.
The neck, e, of the shoe, Fig. 16, must be always coated
with some stuff before the head is put on. Some use a coarse
stuff like that of gunny bags; but the usual and best way is
the following: Strips of pine wood are cut from one-half to
three-quarters of an inch wide, one-quarter of an inch thick,
and as long as the neck is. These strips are laid around the
neck, as represented in Fig. 17, Tab. I, and tied with a
string. The shoe is then placed on the die in the battery,
and the socket with the stem dropped over it. Two or three
blows with a heavy hammer or sledge are then again required
at the top of the stem. The battery is then allowed to play
slowly, so that the stamp is lifted six or eight times while the
others are at rest. It is understood that the shoe is not
allowed to strike on the naked die; but there must be a
piece of a board or plank between. The lining with strips.
of wood must have substance enough to prevent the edge of
the head coming in contact with that of the shoe.
The usual size of a shoe is eight inches in diameter and
*The working effect of a stamp depends on its weight, p, and the height of fall,
h, the product giving the vis viva or live power of the fall, ph=w If p_is
expressed in pounds and h in feet, the product will give foot-pounds; but it is
72
REDUCTION.
six inches high; the neck five inches high, from four to
four and a half inches in diameter at the larger base, and
three and a half to four inches at the top. The best mate-
rial for the shoes is white cast-iron. The chilled shoes are
inferior, as there is always softer iron towards the center,
which causes an irregular wear, reducing the crushing effici-
ency.
The shoe ought to be removed when worn to about an
inch. If allowed to wear more, the rings of the heads will
be attacked and weakened by degrees. On account of ine-
quality of iron, the wear of different shoes in a battery is
never the same; so that the renewal takes place at different
times, which is also more suitable for the whole machinery.
It is, therefore, not proper to turn out a shoe of two or two
and a half inches thickness, because it can be done occasion-
ally with another one which is worn down to one inch or less.
The wear of a shoe ranges between one-half and one pound
to each ton of hard quartz.
G. The Tappet, Tongue or Knob.-Each lifter or stem has
evident that a shoe with too large a base or face will execute less crushing than a
properly shaped one of the same weight, because on the former the effect of the
stroke is too much divided on a large surface. There must be sufficient vis viva
on a square inch of the face. If, therefore, f, represents the surface of the shoe-
ph
base in inches,
W
w' must have a definite value, depending, however, on
f
f
the hardness of the rock to be crushed and to be determined by experience. This
definite value of w' Rittinger adopted:
For very hard rock.
For hard rock.
•
For middle rock..
•
at least w'
6 foot-pounds.
W'
5 foot.pounds.
•
W 4 foot-pounds
In California, for hard rock, w' is about equal to seven foot-pounds. If, there-
fore, for instance, having a hard quartz in view, one square inch of the shoe
requires seven foot-pounds, the surface of the shoe is easily found. Taking the
weight of a stamp five hundred pounds, and the lift, nine inches,
fourths of a foot, the total living power of the stamp
foot-pounds. Consequently the area of the shoe face is
three-
at its fall is 3.500 375
375
7
53.6 square inches,
which reduced to the diameter of a shoe would be nearly 8.3 inches, which in
practice is generally given eight inches.
REDUCTION.
73
a projection or shoulder, by means of which the stem is raised
by a revolving cam. The tongues, as used for wooden
stamps, differ in construction very much. They are made of
wood; but of late iron tongues are applied also to wooden
stamps. The tongues mostly in use have the shape shown in
Fig. 18, Tab. I. A, side, B, top view. The stem has a slit,
through which the part c of the tongue is fitted, so that the
two wedges, d, can be driven in tight on the back of the stem.
In order to save the tongue from wear, its lower face is gen-
erally lined with wrought-iron from one-half to three-fourths
of an inch thick. The iron tongues have the construction
represented by Fig. 19, Tab. I. The opening in the stem
must be sufficiently high to allow a higher setting of the
tongue when the shoe wears out. When fixed in its proper
place, the tongue is wedged above and below. This mode of
fixing the tongue seems to possess more firmness and stability
than the different other ways, where the tongue is attached
only to one side, being fastened by a bolt, which goes through
the stem, or is in the shape of a muff, which slips over the
stem, and is fixed at the proper height by a wedge. Similar
to these are the tongues used on iron stems of a square sec-
tion. To diminish the friction between the tongue and cam,
the first was supplied with iron rollers. This has been tried
also in California, but the result was not satisfactory. In
some places the stamps are provided with rollers or solid
tongues on the top, having various arrangements. Most of
the wooden stems which were used in California had a slit of
about two inches width, through which the cam passed,
catching and lifting the stem at the upper end of the slit.
The friction on the lower guides is considerable. On that
account iron guides were attached to each stem, corres-
ponding with iron guides in the wooden braces.
The California tappet is shown in Fig. 5, Tab. II. A,
shows the horizontal, B, the vertical section. There is a
wrought-iron gib, a, two inches wide and as long as the tap
*Wheeler's gib-tappet.
6
74
REDUCTION.
pet, or shorter, as seen in B. Its inside face forms a part of
the circular hole for the reception of the stem. b, b, are
two key-seats, into which the gib, a, projects a little, so that
a key driven into the seat will press the gib, a, against the
stem, and fasten the tappet to it. This is the most simple
and most effective way of fixing a tappet to a stem, offering
at the same time the advantage of being easily moved to any
given point as may be required by the wear of the shoes.
The stem has its full size the whole length, not being weak-
ened by cuts or screw threads.
When the tappet is worn on one side, it can be turned, as
both sides are perfectly alike. Too much use of grease or
oil prevents the revolution of the stamp, and is very injuri-
ous. In consequence of not revolving, not only will the
surface of the tappet become damaged, but also the advant-
age of a uniform wear of the shoe is lost. A tappet of the
usual size weighs about sixty-five pounds; a stem of eleven
feet length and two and three-fourths inches in diameter,
about two hundred and twenty pounds; the head, eight
inches diameter, sixteen inches high, one hundred and eighty-
five pounds, and the shoe about ninety pounds, which makes
altogether an equipped stamp of five hundred and sixty
pounds. The medium-sized stamps weigh from six hundred
to seven hundred and fifty pounds. Heavy stamps over
eight hundred pounds are less frequently in use.
One stamp
requires about one and a half horse power.*
The round or revolving stamp had formerly iron guides.
The friction, however, was injurious to the stems. For this
reason none but wooden guides are now made, even in iron
batteries. Oak is the best material, but pine is used to a
great extent, the former being expensive. As there is more
*The mechanical effective power per second of the stamps in a battery is found
by the product of the number of stamps, the weight of one stamp, the lift in feet, and
the number of lifts per minute, divided by sixty seconds. The power applied on
the shaft must be greater than the effective power, on account of friction of stamps
in the guides, friction between the cams and tappets, friction of the shaft journals,
and jarring of the whole machinery. Taking for these frictions the same co-effi-
cient as is found with the best constructed wooden stamp batteries, which is one-
REDUCTION.
75
friction on the lower guides, i, Fig. 1, Tab. II, than on the
upper, ', the former are commonly made wider, ranging from
ten to eighteen inches. Fig. 8, Tab. II, represents a wooden
guide for revolving stamps. It consists of two pieces. a, is
the back part, fastened by two or three screw bolts to the
cross-brace (i, Fig. 12, Tab. I). b, is the front part, which is
made of one piece or more. Generally there are as many
single pieces as there are stamps in the battery, each being
bolted by four bolts, which reach through the brace. c, c, are
the guide holes. The circular shape of c assumes an oval
one by the friction of the stem, as shown by the dotted lines,
d. In order to bring the guide hole back to its former shape
after some weeks' run, there are small wooden lists, e, on each
side of the guide hole, which are removed when the holes
appear oblong. The bolts, g, must be examined every day,
and tightened up if one should get loose.
H. The Cams are the last important parts of a battery by
which the stamps are lifted, The cams are made of hard,
tough wood, cast or wrought-iron. Those of iron are pre-
ferred, on account of more durability and less friction,
although it is not proper to let iron work on iron. Cast-iron
cams, especially in a shape as used in California for round
stamps, are more exposed to breakage than wooden ones.
But this cannot be considered as a serious objection, since a
breakage occurs only in consequence of carelessness.
The fitting of cams to wooden shafts is more troublesome
third of the effective power, the calculation of the power required for a five-stamp
battery, six hundred pounds cach stamp, lifted nine inches high, three-fourths
of a foot, seventy-five times per minute, will be the following:
600X 50.75X75
60
2812.5 foot pounds per second;
and 4-32812.5=3750 foot-pounds per second, including friction, co-ef:
3750
6.82 horse-power for the battery; or
550
6.82
1.36 horse-power required per stamp.
5
LO
76
REDUCTION.
than to iron ones. Usually a cam consists of the face or
lifter and the tail or shank, which is fastened by screws or
wedges directly to the shaft, or to collars. The curve of the
cam face, as generally constructed, is the involute of a circle,
which is explained further below. The involute curve
described is the only true line of cams by which during the
lift always one and the same point of the tongue or tappet is
kept and lifted vertically and perfectly uniformly, so that the
lift of the stamp is always in proportion with the motion of
circle which the cam describes.
The face of wooden cams is from four to six inches wide,
according to the weight of stamps. Iron cams have gen-
erally a face of two to two and a half inches. The best
approved shape of wooden cams to be fitted to wooden shafts
is shown in Figs. 6 and 7, Tab. II. Fig. 6 is the side, and
Fig. 7 the ground view. The shank, b, is dove-tailed, in
order to be keyed and wedged into the corresponding hole
passing through the shaft. Iron cams have a similar shape,
being wedged in the same way, but also screwed by two or
three strong bolts to the shaft. In both instances the shaft
is considerably damaged by so many holes, which widen by
degrees. The loose cams must be wedged over, and frequent
repairs are required. For this reason, iron rings, of which
there are as many on the shaft as there are stamps, are pref-
erable. Each ring has two or three boxes, in which the
cams can be fastened by wedges.
Iron shafts are more in use than wooden ones, although
there is some objection to their small diameter, so that only
two cams can be used, unless they are longer than necessary,
and therefore place the shaft further from the stamps, gain-
ing thus a larger lifting circumference. In some places the
iron shafts are provided with drums for the reception of cams.
Using revolving or split stamps, the above objection cannot be
raised. There are also in place of a drum, iron discs, cor-
responding in number with the stamps, attached to the shaft.
Over these discs others of a ring-shape are fitted, having a
wide face with ribs, to which the cams are bolted. There
*Saxony.
*
REDUCTION.
77
are also double discs, on the periphery of which iron rollers
replace the cams. This construction gives no better satisfac-
tion than ordinary cams.
The boxes used for iron shafts on wooden frame-work, gen-
erally one on each upright, are mostly corner boxes.
The cams used in California for revolving stamps are
double-armed. Single cams, as shown by d, in Fig. 1, Tab. II,
are less frequently in use, and principally for the purpose of
increasing the number of lifts per minute. Aside from the
speed of the shaft, which is doubled by the use of single
cams, the force of the stroke against the tappet is injurious
to the whole machinery, and causes a commotion by which
the co-efficient of friction is increased, requiring, therefore,
more power on this account. There is also more danger of
breaking a cam or tappet; and, on the other hand, no real
advantage is offered by single cams. In almost all mills,
seventy to eighty blows per minute are given to stamps
weighing from five hundred to six hundred pounds, moved
by double-armed cams. Even this speed is rather too much ;
and if single cams increase the speed still more, it is not
advisable to adopt them on that account.
The consequence of over-driving heavy stamps to from
eighty to ninety blows per minute, will be a periodical refit-
ting and overhauling of all the machinery as a necessary
result. The efficiency of stamps running over a high rate
does not increase in proportion with the speed, for the reason
that sufficient time is not allowed for the splashed-off parti-
cles to fall back under the stamp before it drops again. This
fact explains also why slow stamping produces more slime
than rapid under similar circumstances.
Limit of Speed in Crushing.-According to experiments
made by J. E. Clayton with a steam battery, six hundred
pounds stamps, nine inches lift, the most productive speed is
one hundred lifts per minute. Mr. Clayton obtained—
In wet crushing..
With 100 strokes.
With 130 strokes.
With 170 strokes
With 200 strokes,
.twice as much as with 60.
very little more than with 100.
as much as with 60.
...hardly anything.
•
78
REDUCTION.
1
One hundred and forty strokes gave the best result in dry
crushing.
The size of the cams is different, according to the weight
of the stamps and the lift; but all have a curved surface on
the same principle.
A cam, as used for heavy revolving stamps, is represented
by Fig. 4, side, and Fig. 5, top view (Tab. III). b, b, are the
arms of the cams; a, is the face, which is ground smooth;
b', represents the rib, and d, the hub, strengthened on both
sides by one-half to three-fourths inch thick wrought-iron
rings, e.
SEC. 18.
Construction of the Cam-Curve.
In Fig. 6, Tab. III, let a be the centre and b the periphery
of the hub of the cam (a, b = four inches). a, c represents
the distance between the centres of the cam and the stem,
equal to a, d, the developing circle of the involute, f, g, h...m.
From a point on the circle, d, at 4, where the axis of the
stem intersects a line, a, 4, which is perpendicular to the
axis of both the stem and shaft, we measure the required
lift; for instance, twelve inches downwards on the circle.
But in order to obtain the curve in such a position that it
shall have a common horizontal tangent with the hub, the
radius, a, b, of the hub, four inches, must be added, so that
for the lift of twelve inches, sixteen must be laid off on the
circle, as shown in the plan, putting the hub radius above
the point 4. The arc, c, 16, is then divided into small equal
parts (the smaller the division, the more correct the invo-
lute). In the figure, the division shows eight parts (two
inches each). From the dividing points of these parts, we
draw the tangents, f, h, i . . . m, and lay off upon each of them
the length of the arc from c to the point from which the tan-
gent is drawn; consequently c2 = ƒ2, c4 = f'4, c6 = 96, and
The points ff, g...m are connected by a curved
line, which gives the involute or curve of the cam.
so on.
REDUCTION.
79
Another mode of constructing the involute is that by
means of circles. It gives, of course, the same result, but is
somewhat more complicated, and cannot be made clear with-
out a figure.
The construction of a cam of natural size in a practical
way is performed by developing the involute from a circle
by means of a thread. The circle, d, Fig. 6, is cut out of a
board, and a thread wound on its periphery to the length of
the required lifting height, plus the radius of b. One end of
the thread is fixed to the periphery, to the other a pencil is
fastened. The circular board is then laid upon another one,
and the involute drawn by unwinding the thread from the
circle, keeping it always strained, until it forms a tangent to
the circle at its fixed point 16, m.
The construction of the cam-curve shows that the distance.
of the cam shaft from the stamp is a definite one in relation
to the cam-curve. The face of the tappet must be always at
right angles to the radius of curvature at each point of the
curve, which passes under it during the lifting motion. As
the face of the tappet is a circular one, the end of the arms,
b, must have a corresponding cut, otherwise the corner point
would damage the circumference of the tappet. There are
cams the end of which has two circular cuts, meeting in the
centre of the cam face. In this case the cam may be fixed
on the right or left side of the stamp, and in case there
should be an unequal wear, they can be moved to the other
side. There are mills where the cams last for nine years,
and longer, if only proper care is taken, not only in greas-
ing, but in keeping the tappet at the proper height and
*
*The use of oil on cams is improper. It is used up too soon; and if too much.
is applied, the friction is reduced, so that no revolving will take place. The grease
must be tough. A thin layer of it should remain between the tappet and the cam
face; but it must be sufficiently lubricating at the same time. Mr. Z. Wheeler,
for this purpose, uses a composition of oil, tar, resin and tallow in such propor-
tions as to form a somewhat thick paste on cooling. The use of this composition
keeps the face of the cam always coated, so that there is no real contact between
the metals. Cams treated with Wheeler's grease show the grinding lines on the
face after several months' run (600-pound stamps). This grease offers the
advantage besides that tappets and cams are kept clean.
80
REDUCTION.
proper distance, so that the full face of the cam works always
uniformly, which depends much on the steadiness of the
stamp, and for which reason no play should be allowed in the
guides. The distance between cam arm and stem ought not
to exceed one-eighth of an inch; but, on the other hand, the
cam must not be allowed to touch the stem at any point. A
wide face (two and a half inches) is preferable to a narrow
one.
The cams are fastened to the shaft simply by wedging
keys into the seat. For this purpose the shaft has generally
a groove the whole length of one battery. The key, made of
steel, must be driven in with much force. In order to set
the cams systematically, the question arises, "Which of the
stamps in a battery must be lifted first? Practical dressers
are not well agreed as to the order in which the lifting of
four heads in one battery should take place; whether one of
the inner pestles should precede the outer, or whether a side
pestle should be first lifted. Preference, however, seems to
be given to the following method, supposing a spectator to
stand in front of a four-stamp battery: Left side pestle first,
right side pestle second, right middle third, left middle last."
SEC. 19.
Order of Successive Stamp-Lifts.
"X
The relative order in which the stamps drop is important.
A battery in which the stamps play in successive order, as
1, 2, 3, 4, does not discharge well. The stuff is generally
pushed towards one side; it accumulates there, and the last
stamp cannot penetrate the mass, so that at times its lift is
not over three or four inches, while the first one keeps its
full lift. It is difficult to keep such a battery in working
order. This spiral arrangement of cams answers in batteries
discharging at one end of the short sides.
*Supplement to Ure's Dictionary, 1863.
REDUCTION.
81
The weight of the stamps must be distributed on the shaft
as equally as possible. It is, therefore, more advantageous
for the power and machinery to apply one shaft to many bat-
terics; because, if there were, for instance, thirty or forty
stamps in a mill, they could be arranged on the shaft in such
an order that not more than one would catch the tappet at
the same instant, and the shaft would bear the same weight
at each moment of the revolution. If the same number of
stamps is driven by six or ten separate shafts, connected
with a main shaft, it may happen that the main shaft bears
four or six times as much at one moment as at another,
depending on the accidental time of starting of each battery.
But there are other reasons which make the use of one shaft
for too many batteries unadvisable. The stamps can be
arrested easily in each battery independently of others; but
in case a cam should get loose, all the batteries have to lie
idle while the repairs are going on. Still more inconvenience
would arise if one of the cams should break. In this case,
all the cams which are in the way must be removed. In this
respect, cams fitted directly to the shaft are inferior to those
screwed or wedged on rings or collars. A middle course
seems to be the best. Two five-stamp batteries with one
cam shaft are better for the machinery than two shafts.
Even twelve stamps (in three batteries) on one shaft, might
be more advantageous than if driven by three separate cam
shafts, since suitable cams and strict attendance are sufficient
to run a battery for years without a breakage. For the
same reason five stamps in a battery answer better than
four; but for convenient manipulation (which, however,
ought not to be the main object) separate cam shafts for
single batteries are preferable.
The position of the cams on a shaft for two five-stamp bat-
teries is represented in Fig. 9, Tab. II. 4, section of the
shaft; B, front view of the same, with perpendicular dotted
lines, 1 to 10, indicating the ten stamps of two batteries.
The half circumference of A (because double-armed cams)
is divided into ten equal parts, commencing at a, 1. Through
82
REDUCTION.
these points of division parallel horizontal lines, 1, 2, 3 ... 10,
are drawn, and in the perpendicular line of each stem the
dots a, b, c, a', etc., marked in the following order, corres-
ponding with the dots in the front view :
On the 1st line, 1st cam for the 1st battery
Cl.
a'.
(C
((
2d
((
1st (C
{t
"
3d
(6
5th
"
((
2d
1st
e.
(C
4th
(6
5th
((
((
"L
2d
é'.
แ
5th
แ
3d
แ
((
1st
((
C.
6th
66
3d
แ
((
(
2d
((
7th
2d
(6
เ
((
1st
¿ ·
b.
8th "
2d
((
(3
2d
(
b'
9th "
4th
((
((
1st
d.
" 10th "
4th
"
66
2d
a·
The points of division upon the circumference of A show
the points of the key-seats, transferred on the cams, as seen
in Fig. 4, Tab. III. The first seat, 1, on the first cam of the
first battery upon the line h, is marked on all ten cams exactly
in the same line. The distance from 1 to 2, then from 1 to 3,
to 4, and to 5, Fig. 9, A, Tab. II, are transferred in pro-
portion from 1 (on the line h) correspondingly on the second,
third, fourth and fifth cam of the first, and in the same way
the distances on the following five cams of the second bat-
tery. When fastened on the shaft, having a long common
key-seat, the cams will stand in order and position as shown
by the dots a, b, c... of Fig. 9, B, Tab. II.
If three batteries should be moved by one cam shaft, the
circle should be divided into fifteen parts, and then proceed-
ing in the same way:
On the 1st line, 1st stamp of 1st battery.
"2d
แ
((
2d
3d
66
{
1st
1st
(C
(C
" 3d
{{
The leading principle of the order of lifts is, first, to dis-
tribute the weight of stamps equally on the shaft; and,
second, to have the adjoining stamp on both sides begin to
rise before the middle stamp drops, so that the rock is thrown
on both dies to the right and left.
REDUCTION.
83
Wooden shafts have their own bearings, independent of
the frame-work of the battery, while iron ones generally rest
on the uprights. There are, however, iron frame batteries
in Europe, the iron shafts of which are in no connection with
the battery frame.
The means of hanging up the stamps without stopping the
shaft are very different. A simple and very convenient
method is represented in Fig. 1, Tab. II. There is a cross-
beam or an iron rod, x, (the first preferable) in front of each
battery, resting on both sides in a cut of the uprights, so that
it can be removed easily. In a half-round groove, if the
support is wood, there are movable arms or hangers, h, with
leather straps, g, at the upper end. The hangers rest in the
position shown in the drawing, and are one inch longer than
the highest lift. In hanging up the stamps, a man takes hold
of the strap, g, with one hand, and with the other places a
stick on the face of the approaching cam before it reaches
the tappet.
The stick is about eighteen inches long, as wide as the cam
face, and one and a half inches thick. The cam, with the
stick upon it, will lift the tappet one and a half inches higher
than usual and half an inch above the hanger, which must be
placed under the tappet at the right moment. In letting
down the stamps, the stick is placed, as before, upon the
cam, and the hanger removed by drawing upon the strap
before the tappet is lifted; otherwise the pull might come
too late.
In order to impart to the falling stamp more speed, long
wooden springs (twelve to fifteen feet) have been tried in
different mills, attached to each stem at its upper end. By
means of screws at about one-third of the whole length from
the fixed end, the spring power could be increased or
reduced. The stems had conical hollows at the top, in which
an iron pin of the spring fitted, so that the stem could
revolve during the lifting. In crushing dry, especially where
the ore is rich in sulphurets, the use of springs effects a
better discharge if screens are used, as the powdered part is
84
REDUCTION.
thrown against the sides with more force. By this means at
the Ophir Works, Nevada, twenty per cent. more of crushed
ore was obtained in the same time.
SEC. 20.
The Discharge in Dry Crushing.
The discharge of crushed ore in dry crushing is effected
either through grates or screens, or by a draft of air. Grates,
when used, generally supply the place of the mortar-bed.
They are sometimes in one solid casting, like common fire
grates, the open space widening downwards; the grate bars are
from six to seven inches deep by one inch thick. This kind
of grate is inconvenient, on account of the iron being beaten
flat, and the openings choked up, which is difficult to remedy
after several inches have been worn away. Mortars, with
movable grates are better, as the wrought iron or steel bars
can be easily replaced by new ones. Figs. 13, 14, Tab. I, show
a grate mortar, such as was used in the Gould and Curry Mill,
Nevada, before wet crushing was introduced. In the vertical
section, Fig. 13, the bars are shown by a, a. They are placed in
the grooves, b, of the mortar. The finely broken ore falls on
the inclined bottom, c, underneath, whence it slides into elevat-
ors, by which it is lifted to the upper stories and discharged
on sieves. The coarser part is conveyed back to the battery.
At d, is the opening for feeding. The battery is closed tight
and is connected with a fan blower, by which the dust is
drawn into dust chambers. In other mills grinders of different
descriptions are used to pulverize the material which passss
the grates. For concentration by compressed air the grate-
stamping is a less suitable material than breakers or rollers,
producing more dust.
Much less complicated is the dry crushing in batteries
constructed like those used for wet crushing, generally dis-
charging on both long sides, but the yield is limited to about
REDUCTION.
85
one-half of a ton to the stamp in twenty-four hours, using
wire-cloth of forty holes to the inch. The quantity, however,
depends much upon the quality of the rock.
Another mode of dry crushing without grates or screens is by
means of a draft produced by a blower. In place of a screen
there is a slit along the battery in a moveable partition, so
that by lowering or raising the same coarser or finer stuff can
be obtained; the dust is conveyed into a chamber. To pre-
vent loss it has been attempted to return the same air from
the chamber to the battery, and thus to keep it in constant
circulation between the two. But this did not succeed.
This mode of crushing gives the most uniform powder, and
finer than is obtained in any other way, but it is too slow.
The dry crushing with sieves on one or both sides of the
battery is the most frequent method in California and Ne-
vada. It is not only simple in the construction, but it
finishes the pulverization at once; unlike the stamping on
grates. If it is not desired to crush fine-which, in fact,
is entirely unnecessary, as twenty holes to the inch of wire-
cloth will discharge a suitable ore for roasting, as well as for
other purposes—the battery will turn out about one ton per
head in twenty-four hours, provided the stamps have a proper
speed and no punched sheet iron, but wire cloth is used. 850
lbs. stamps, seventy to seventy-five drops per minute, fifty
meshes to the running inch, crush 0.8 ton per head in
twenty-four hours. Ore for dry crushing must be perfectly
dry; the sieve must stand inclined, as represented at o, in
Fig. 3 B., Tab. II., and not too high above the dies.
The dust arising from crushing the ore is not only injurious
to the lungs of the workmen, but also destructive to ma-
chinery. For this reason all the batteries are closed as
tightly as possible, and the mortars are connected with a fan
blower which draws the air and dust from the batteries into
dust chambers. These chambers, one or more in connection,
require a considerable space ;-from eight to fifteen thousand
cubic feet-moreover, the air must have an outlet which will
carry out the finest part of the dust. The plan of condensing
86
REDUCTION.
this escaping dust in an inclined canal by steam would pro-
bably allow a smaller dust chamber, preventing at the same
a loss. If an open battery is used, with a movable hori-
zontal sieve in front, the finer sieve being protected by a
coarser one, generally perforated sheet iron, the ore can be
sprinkled over with water, which lays the dust to some
degree. Care must be taken, however, not to use too much
water, which would stop the sifting.
The simplest way of obtaining a draft through the mortar,
and to prevent dusting in dry crushing,* is J. E. Clayton's plan,
by means of a steam jet. A pipe of about nine inches square
section leads from the upper part of the closed mortar into a
condensing room of small size, open on the top. Near the
mouth of this pipe, a few feet back, a jet of steam is intro-
duced, discharging through it into the chamber, and thus pro-
ducing a strong draft of air from the mortar through the pipe
to the chamber. This draft carries off all the dust, while the
steam, condensing in the chamber, precipitates the dust with
the resulting water.
For the purpose of drying ore, after it is reduced to the
size suitable for battery, there is a floor of cast iron plates
with fire canals underneath, either in front of the batteries.
or in some other convenient place. The damp ore is spread
upon the hot floor, and sometimes shoveled over till perfectly
dry.
SEC. 21.
Discharge in Wet Crushing.
The discharge in wet crushing is effected either on the
short or long side of the battery.
In the first case, iron bods are sometimes used; but those
of rock are more common. Ore and water are introduced at
one end near the battery post, and the pulverized matter dis-
charged at the other end, generally through the upright, so
that the charged ore passes under all the stamps before
*Applying sieves for the discharge.
REDUCTION.
87
reaching the outlet. It is quite proper here to fix the cams
in a spiral line on the shaft. In batteries of this kind, the
stamps have either a different weight or a different lift, or
lift and weight both vary. In some places, the first, in
others, the last stamp, is the heaviest with the least lift.
The discharge hole, three to four inches wide and about nine
inches high, leads the stuff through the upright either
straight, or if the upright separates two batteries, in a
broken line. Putting a plug in the bottom of the hole
deepens the stamping bed, and the crushing produces a
finer powder. Other batteries of this kind have the dis-
charge on both ends, close to the upright posts. Others
again have perforated plates or sieves at one end, leaving
about six inches space between them and the upright
through which the outlet is made.
Much more extensively used are the batteries, having their
discharge on one or on both of the long sides.
The discharging arrangements are different. The general
mode is that of discharging through a slit or longitudinal
opening. A trough or mortar of this kind has a discharge
opening the whole length of the battery. The breast plank
is fastened to the upright posts by means of cramps, on which
the plank can be raised or lowered, thus regulating the width
of the opening. A deep mortar trough and a narrow opening
produces fine crushing. The higher the bottom, i. e., the
shallower the mortar trough, the coarser is the discharged
material, but the coarse grains are very unequal in size, so
that this mode of discharging is more suitable for fine crush-
ing. The discharge is generally on one side of the battery.
The best arrangement for coarse and fine crushing, (that is,
production of fine sand, not slime) consists in the use of
grates or screens. The grates are made of wrought iron
staves set in a frame, closer or wider apart as may be re-
quired, and standing vertically. For screens either punched
copper or iron plates are used, less frequently brass or steel
wire cloth, although the latter is more effective in discharge,
as a wire cloth will have always more openings of the same
size in a square inch.
88
REDUCTION.
The grates always stand perpendicular, and reach to the
bottom of the battery. They do not choke as much as the
screens, and discharge freely.
The punched sheet-iron screens are most in use.
In some
mills the screens are set in a perpendicular position. To
prevent choking, there are sometimes wooden hammers in
connection with the shaft or some other motive power, which
strike the screen at regular intervals. If no such arrange-
ment is present, the sieves must be brushed from time to
time. Punched holes will always be smoother and somewhat
wider on the side where the needles were applied. This
side must be on the outside of the battery.
An inclined position of the sieves, as represented by o,
Fig. 1, Tab. IV, is much preferable to a perpendicular, as
the discharge is increased considerable. It has been thought
that sieves in an inclined position are more liable to be
choked; which, however, has not proved to be the case—at
least not with a slight inclination, as now used in California
and Nevada. It might be different, however, with wire-
cloth, which, not being so smooth, might retain the grains
more in an inclined than in a vertical position. Still there is
more advantage in using inclined screens.
A very good way to prevent the choking of sieves is an
arrangement by which the pressure of the water from inside
the battery against the sieve is counteracted. This is easily
accomplished by having the sieve enclosed also on the out.
side, so that the water stands level on both sides of the
screen, leaving a space of two or three inches between the
sieve and the board partition. The bottom of this compart-
ment is inclined from both sides towards the centre, where
at the lowest point is a round opening, adjustable by a slide-
gate. By means of this gate the water in the battery is
regulated and kept at the required height. The grains
which cannot pass the holes of the screen fall back under the
stamps, as there is no pressure on the grain against the
screen-hole. The screen is kept clean for several weeks-
that is, as long as the screen stands the wear, which depends
on the distance from the stamps and on the weight of stamps.
REDUCTION.
89
The Screens used in California and Nevada are made of
Russia sheet-iron. Generally the number from 1 to 10 indi-
cates the sizes of holes corresponding with the needles used
for punching, so that No. 1 is the coarsest. Many mills,
having a sufficient number of pans, use No. 2 or 3; but No.
4 is generally used. The round holes of No. 4 have one-
twenty-fourth of an inch diameter, and there are one hundred
and forty-four holes in a square inch. Mills having a smaller
number of pans in proportion to the stamps, use No. 6;
holes, one-fortieth of an inch in diameter-three hundred
and twenty-four to the square inch. The sheets are, accord-
ing to the mortar, generally about three and a half feet long,
and from ten to fifteen inches wide. The wooden screen
frame is lined with strips of blanket, and the screen is tacked
over it. The blanket makes a tight joint, and facilitates the
removing of the tacks when the screen has to be replaced
by a new one, or needs to be turned, so that the worn and
mended lower part is turned uppermost. In this way a
screen can be used for several weeks longer.
It is,
Brass wire-cloth makes a fast-discharging screen.
however, expensive, and for this reason used only for dry
crushing. The punched screens are very perfectly made,
and answer the purpose. If very fine stamping is required,
it is more advantageous to crush without sieves than to apply
wire-cloth of eight thousand one hundred holes to the square
inch, as has been done in several mills. A mortar, with a
slit and deep bottom, as further described below, produces a
fine stuff, but has a slow discharge.
Although there are many stamp works yet in operation
where the discharge is only on one of the short sides of a
battery, this mode does not offer any real advantage. It is
claimed that the particles are crushed smaller by degrees
passing from one stamp to another. It is, however, difficult to
understand why on this account a preference should be given
to a slow operation. For the purpose of concentration, it is
*Made with great perfection at the Union Foundry, San Francisco.
7
90
REDUCTION.
one of the first principles in crushing that each particle
should escape the battery instantly when crushed to the
required size. To accomplish this as near as possible, the
discharge on the long side is far more suitable, and is cer-
tainly the best method if the discharge takes place on both
sides. In California and Nevada, in several mills, the dis-
charge through screens takes place on the two long sides in
dry and wet crushing; but discharge on one side is the gen-
eral mode. The dies are two to three inches below the
discharge, and there is very little variation in the mode of
crushing, for the reason that up to this time the direct con-
centration of ores has not been practiced, and, consequently,
no attention has been paid to the nature of the ore in crush-
ing, but only to the quantity which could be crushed in a
certain time.
The experiment has been tried in California, of making
separate compartments in the mortar for each stamp. Each
compartment had its own screen. It might have been antic-
ipated that, having four stamps in the battery, the discharge
could not gain by diminishing the screen surface; but it
would seem that, as the space in one compartment was very
limited, the stuff could not be thrown about so much, and
would be forced to find its way through the screen. It was
discovered in Europe, long ago, that six stamps in one bat-
tery did not discharge as well and regularly as they would in
two three-stamp batteries. To obviate the necessity of the
middle post or upright in framing, the mortar of six stamps
received an iron or wooden partition in the middle. These
batteries are called "double batteries."
SEC. 22.
The Feeding of Batteries with Ore.
The feeding of batteries with ore is performed either by
hand or by mechanical contrivances. The feeding by hand,
REDUCTION.
91
if a skillful feeder attends the stamps, is preferable to an
improper feeding apparatus. He can keep the batteries.
always provided with so much ore that the crushing and dis-
charging is regular, and to the best advantage. One man
can supply with ore, batteries which crush twenty-five to
thirty tons in twenty-four hours, provided the rock is already
broken to the required size and stored in front or close to
the stamps. He is guided principally by the sound of the
stamping; but his attention must be directed also to the
sieves, cams, tappets, oiling, etc. Unreliable feeders not
only neglect the batteries, but their feeding, especially at
night, is so irregular, by over-feeding at one time, and too
little at another, that the yield of the crushing falls short.
It is doubtless easier to construct a proper self-feeder than to
have always able feeders at the batteries. Hand feeding
seems to have yet the preference in California and Nevada,
although a great many mills are provided with self-feeders.
There are two kinds of self-feeders-stationary and mova-
ble. In both cases the stamps regulate the feeding them-
selves.
Stationary hoppers are capable of holding so much rock as
is required for twelve to twenty-four hours' stamping. In
this respect they are preferable to the movable ones, which
are smaller, but more convenient, and easy to regulate. Fig.
10, Tab. II, shows a stationary feeder, as used in Freiberg
(Saxony). a, is the hopper, with a sufficiently inclined bot-
tom, b, made of planks, and lined with boards or sheet-iron ;
c, is a beam, in the upper side of which is cut a hollow, d,
commencing below the opening, e. The beam rests on a
cross-piece, g, and is kept from sliding by the nose, f.
Between the beam and the bottom of the box is a space of
about two inches. When the stamp, in want of ore, strikes
the rod, i, the lower part of the beam is pushed down, while
the upper end strikes at the bottom of the hopper. The
imparted jerk causes a slide of the ore. k, is a slide door to
regulate the opening, e. Similar hoppers are used in Corn-
wall an also in California; but there is no pitching-rod, i.
92
REDUCTION.
*
The gradual discharge is promoted by the commotion im-
parted from the battery. It happens sometimes that the
discharge opening is stopped up by the rock. In order to
clear it immediately, there must be sufficient room for this
purpose between the hopper and the battery.
The movable feeders receive their motion from the middle.
stamp if only three in a battery. Four or five-stamp batter-
ies are generally provided with two self-feeders. There are
various contrivances of this kind in use. The shape is that
of a square or oblong box. The bottom stands always
inclined more or less, according to the stuff; but always so
that in a state of repose no sliding of rock could take place.
The box rests about one-third of its length toward the bat-
tery on its axle; the other end on a fixed support.
Sometimes the box is so constructed that the hind part is
lifted by a rod, which is in connection with a lever, on the
other end of which a blow is imparted by a screw fixed at
the top of a stamp. The screw regulates the strike, and
must be screwed shorter in propertion as the shoe wears.
Another arrangement, represented by Fig. 7, Tab. III, as
used in Hungary, has been applied also in California. The
feed-box, a, wider on the top, has an inclination of fifteen to
sixteen degrees, and stands on two legs, b, fastened to the
axles, c, c. In this position the box has a tendency to slide
forward; the block, d, touching the battery or some other
fixed arrangement, keeps the hopper at rest. Above the
hopper there is a small shaft, e, attached to the upright of
the battery, having an arm, f, which receives the percussion,
and two others, g, each of them touching a projection on
each side of the box inside. A blow transmitted by the rod,
h, to f, pushes the hopper back by the arms, g. In falling
against the battery, the ore slides out from the blow received.
There is no packing, even when the ore is muddy, in these
hoppers, as in those where the percussion acts from below.
A self-feeder frequently used in Nevada is shown in
side view in Fig. 11, Tab. II. The feed-box, a, of which
there are generally. two to each five-stamp battery, is a fixed
REDUCTION.
93
box with a movable feed shoe, b, resting on the support, c.
The rod, d, is connected with the lever, e, which rests on a
half-round pin, f. The space below f, serves for regulation
of the position of the lever, being filled with a wooden piece,
higher or lower, as the shoe of the stamp may require by
wear. By the screw-thread of d, the slide of the shoe, b, can
be altered. The depth of the box, a, varies with the quan-
tity of rock which it should contain. Smaller boxes of the
size of Fig. 11 are preferred, although it would seem that
there is more advantage in filling a feed-hopper once a day
instead of four or six times.
In some mills, the lever, e, is so short at g, that the tappet
is allowed to slide by with a moderate strike. By this
arrangement a permanent feeding is effected, which, of
course, must be perfectly proportionate to the discharge.
But it must be considered that if, for instance, the discharge
should decrease by choking of the screens without being
observed in time, the feeding would proceed at its usual rate,
fill
up the battery, and burst the screens. It may also hap-
pen that a sieve breaks, and in this case the discharge would
increase and the stamps soon strike on the bare dies. A mill
of thirty or forty stamps makes so much noise that it is not
always possible to detect such irregularities immediately by
the sound of the stamping. For this reason the old advice
deserves consideration, which counsels to fix a rod connected
with a bell between the two uprights, in such a way that any
stamp reaching the naked die, will strike the rod with the
tappet and ring a bell.
SEC. 23.
Quantity of Water Required for Crushing.
The quantity of water necessary to carry the pulverized
ore out of the battery is usually conducted in an iron pipe,
which is generally fixed on the feed side, where it can be
94
REDUCTION.
seen by the feeder or watchman. The quantity depends on
the quality of the ore. Pure quartzose ore requires less.
water than clayey stuff. Coarse-grained ore or gold can
bear more water than in a very fine condition. Floating
metals and slimes increase with the decreasing quantity of
water. The stamping of muddy, clayey ore requires some-
times more water than necessary for a proper discharge. In
this case water can be conveyed to the stuff outside the bat-
tery. The settling of ore particles is more perfect in a
sufficiently diluted condition of the pulverized mass. In
crushing quartz rock in the usual way with a No. 4 screen,
each stamp requires from one-half to three-fourths of a cubic
foot of water per minute.
SEC. 24.
Remarks on Speed and Weight of Stamps.
"The stamping process is not so simple as it may appear
at first sight. Many of its particulars, such as the form of
mortar, mode of exit for the stuff, weight and rapidity of the
pestles, and quantity of water employed, must be varied to
suit the mode of dissemination and the structure and char-
acter of the ore, as well as of the matrix. Fineness of reduc-
tion is by no means always a desideratum, for if some kinds
of stuff be reduced too fine, much of the ore contained in it
will be wasted. Hence, considerable judgment is necessary
in selecting the grate best adapted to the stuff to be operated
upon....
99%
In California and Nevada, as already mentioned, in con-
structing a mill, no consideration is paid as to the require-
ments of crushing for concentration. For this reason the
mode of conducting the water into the battery, the quantity
of it, the number, shape and rapidity of the stamps, their
lift and the depth of the trough-that is, the distance from
*Supplement to Ure's Dictionary.
REDUCTION.
95
the dies to the rim of the discharge-are very much alike,
and differ principally only in the weight of stamps and such
contrivances as would increase the quantity of crushed stuff
in a given time. In the gold mines, however, the use of
quicksilver in the battery is sometimes the cause of a differ-
ent construction of the battery, not always advantageous for
the crushing itself. The dies, for instance, are laid four to
five inches apart, for the purpose of offering ample room for
the accumulation of amalgam.
As a general rule, heavy stamps are more effective as to
quantity than light ones, without exception. But also, in
regard to the quality of the crushed stuff for concentration,
heavy stamps are generally preferable. This depends very
much on circumstances. A particular treatment of a certain
class of ore by lighter stamps, demanding more time, may be
remunerative in Europe, while gain in time by the use of
heavier stamps may be important where labor and everything
else is high. Nevertheless stamps and lift must be, to some
extent, in accordance with the hardness or softness of the
ore; but the choice depends also on other circumstances.
Quartz containing brittle silver ore, to be crushed for con-
centration, requires lighter stamps than the same ore if
crushed for the sole purpose of amalgamation in pans.
There are many mills in California with eight hundred to
nine hundred pound stamps, especially where a hard, flinty
quartz occurs, with a lift of twelve to fifteen inches.
Although the general opinion is in favor of lighter stamps of
between five hundred and seven hundred pounds, the mills
employing heavy stamps profess to do better than with light
ones. The most common stamps are those between five hun-
dred and six hundred pounds, with from nine to twelve
inches lift. These batteries, if well attended, will doubtless.
stand for many years longer than those with nine hundred
pounds stamps.*
*The danger, however, involved in using heavy stamps is not quite so great as
Prof. Gatzschmann would lead us to believe, by publishing, as he does, with apparent
seriousness, on page 370, Vol. 1, of his “ Aufbereitung," the following California
96
REDUCTION.
In some mills the attempt has been made to compensate
the loss of weight from wearing of the shoes by adding old
tappets on the stem; but, although well enough, this has not
been imitated, and it seems that, considering the total weight
of a stamp of six hundred pounds, a gradual decrease to
about five hundred and thirty pounds is too inconsiderable to
afford an advantags in burdening the upper part of the stem.
It would be much better to have the shoes cast four inches
high in place of six when the difference of weight by wear
would be still less, but the shoes would need to be oftener
renewed. For the last reason, shoes four inches high are not
much in use.
High lift, light stamps, and a deep mortar are used for fine
crushing. For coarse, it is found more effective to have
heavier stamps, less lift, a shallow mortar, and more speed.
The quantity of rock which can be crushed, of course
depends very much on the nature of the ore, weight of
stamps, speed, size of screens, etc. Six hundred pound
stamps will crush from one to three tons per head in twenty-
four hours at a speed of seventy-five blows per minute, using
No. 4 and 5 screens.
The speed of the stamps is important not only as respects
the quantity, but also the quality of the crushing. A slow
motion will produce more floating stuff, or crush finer, than a
rapid one, because with quick dropping of the stamps, ore
particles of a small size do not find time enough to fall under
the shoe, and are carried out, while, with a slow motion, many
grains which could pass the screen slide under the stamp,
and are pulverized finer than required. Although it is evi-
dent that a higher speed will crush more stuff in a certain
time, yet there is a limit, beyond which the speed should not
story:-
"The Mining Journal, Vol. XXII, page 207, says: They have there (in
California) in a steam mill, erected stamps of a thousand pounds weight and
several feet lift. On starting them, they (the stamps) flew high in the air, and
stamped the bottom and the whole frame-work into the ground
The spectators
ran off horrified, and gazed from a distance until all was destroyed." It is not
stated in what place this occurred, nor who was the famous builder and starter of
the mill.
REDUCTION.
97.
be increased. The stamp must fall on the ore with its full
weight and force; the revolving stamp must have time to
finish its revolving motion. An extremely quick or sudden
blow is less effective, besides involving the danger of a tap-
pet being caught by a cam while dropping. For stamps
weighing from five hundred to six hundred pounds, a proper
speed is seventy blows per minute; but over seventy-five, as
practiced in some mills, is rather too much.
SEC. 25.
Reduction by Rolling Mills.
Construction. These mills are more employed than stamps
for reducing ores to a coarse size. The mill consists of two
rollers, fitted in a strong frame-work of cast-iron. They lie
horizontally, revolving against each other, and crush the ore
while it passes between them. Generally there are several
series of rollers, set below each other, so that the upper pair
prepares the ore for the lower. The parts of which a rolling
mill consists are the rollers, bearings and frame-work.
The rollers are smooth, or sometimes corrugated. The
latter are used to break the rock roughly, preparatory for the
lower pair beneath. The shape of a roller is cylindrical;
but, as generally used, they are short, the diameter being
larger than its face. The usual size of rollers is from
eighteen to twenty-four inches diameter. Larger rollers are
less convenient and too heavy, although the wear is slower
on account of the greater surface, and they catch the stuff
better and work smoother.
The speed at the circumference ranges between one and
three feet per second, so that eighteen-inch rollers revolve
from twelve to thirty-eight, and twenty-four inch rollers from
ten to twenty-nine times per minute. With equal length of
98
REDUCTION.
rollers, the speed depends on the quantity of ore to be
crushed. Too much speed must be avoided, because more
dust is created, and the machinery is more exposed to break-
ages. Too slow a motion is again injurious, for the reason
that the efficiency of the machine is not utilized entirely, and
because the wear of the rollers is less uniform.
To impart a higher speed to one of two rollers, either by a
greater diameter with the same number of revolutions, or by
increased speed, to one of two equal rollers, does not offer a
practical advantage.
The length of rollers is from three-fourths of a foot to three
feet. Short rollers are preferable to longer ones.
As the wear is not allowed to be more than a half or one
inch on each roller, the latter is not made in one piece, but
the axis is separate, except with small ones, which are cast
in one piece. The ring or mantle is from one and a half to
two inches thick, and can be removed and replaced when
The mantle is chilled and hardened, being cast in
smooth cast iron moulds, so that no turning is required.
worn.
One pair of mantles of one foot length can crush about
three hundred tons of quartzose ore before being worn out,
reducing it from two inch pieces to one-third of an inch.
There are different means of fastening the roller on the
axis. The axis or shaft has usually a larger diameter than
the pivot. Tab. II, Figs. 17, 18, represent an efficient plan
for fastening. The cylindrical roller, Fig. 17, is fitted with
four internal projections, a, as long as the groove, b, b, and as
wide as the narrow part, c, of the groove. When the cylinder
is to be fitted on the axis, the projections are introduced into
the recess c, the cylinders turned until they fit into the wider
recess between b, b, and then wedged to the axis by a close-
fitting key.
Another way is the following: After the inside of the roller
and the axis have been turned smooth, so as to fit each other
perfectly, the axis is introduced into the roller, and on the
contact line of both are bored three or four holes, wedged by
fitting keys, as shown by Fig. 18, Tab. II.
1.7
YOF
99
REDUCTION.
Very frequent, also, is the plan of fastening the mantle by
means of wooden wedges of one to one and a half inches
thickness. These wedges are driven tight all round the axis,
so as to have each point of the roller equally distant from the
center. When the mantle is worn out, the wedges are either
burned out or the mantle broken.
The Frame is generally horizontal and sufficiently heavy to
resist the power applied to the rollers. It is bolted to a solid
wooden frame, and all the parts are bolted together by iron
rods. Tab. II, Fig. 15, a side-view; Fig. 16, a ground plan,
show the construction of a pair of rollers. On the bed-plate,
a, are two standards, b, as far apart as the dimensions of the
rollers require. The bed-plate is firmly bolted to the bearer,
c, which usually rest on masonry. Both parts of the frame.
are bolted together by the bolts, e, e. Between the stands, b,
of each frame, are the bearings, f, so arranged as to slide in
grooves, or some other arrangement, permitting the cylinders.
to be brought nearer, or to be separated from each other.
Above the bearings is a strong rod, h, which strengthens the
standard and serves as a guide for the bearings. To keep
the rollers in contact, and yet allow a separation in case an
obstruction should take place, there is a weighted lever, i,
hung to the standard at 7. The short arm, k, of the lever,
presses on the pin, n, which, passing through the standard,
touches the bearing, f. Whenever a piece of iron, or any-
thing else too hard to crush, comes with the ore between the
rollers, the roller on the lever side will act through the bear-
ing pin, n, on the lever, which being lifted allows the passage
of the obstruction, pressing the roller again to its former
position.
In order to change the weight of the lever, there is either
a box hung at the end of the lever in which the weight may
be added or taken out, or, as represented by the movable.
weight,, the lever can be lengthened or shortened.
The driving wheels, r, require to be placed some distance
from the rollers, so that any undue opening of the latter may
100
REDUCTION.
not vary the pitch line of the wheels, ", to such an extent as
to endanger the safety of the teeth; for this purpose the axis
of the rollers must be connected with those of the driving
wheels by tumbling shafts, o, coupled by muffs, 3.
The most simple frame for rollers consists of four wooden
vertical posts, seven by eight or eight by twelve inches
thick, and at least twelve feet high. About six feet above
the ground the journal boxes are bolted to the posts. This
arrangement has the advantage of taking up less room, pre-
venting at the same time a breakage, in case an obstruction
should come between the rollers, as the posts, being elastic
yield so much that the obstruction can pass between the
rollers. The boxes must stand vertically, as the main pres-
sure is a horizontal one.
Between the rollers and the driving gear are the tumbling
shafts, requiring four other posts of the same kind, so that
the whole frame is composed of eight upright posts, each
four in one line, with base, cap, and cross-beams.
Mackworth's crushing rollers are made conical, to equalize
the wear, and as one roller travels faster than the other, the
fragments are partially turned over, so as to present their
weakest line of fracture to the direction of the crushing force.
It is claimed that these rollers work with less power. In
lieu of the counter-balance weight, usually employed to allow
the rollers to separate and pass excessively hard fragments,
and to bring the rollers together again, the machine is made
more compact and simple by connecting the two brass collars,
in which the rollers work, by a number of bands or cords of
vulcanized India-rubber strongly stretched. A compound
cord of India-rubber, three inches in diameter, composed of
one hundred and forty-four small and separate cords, when
stretched to double its natural length, gives a strain of three
tons. The brass collars do not revolve.
As the crushed ore is composed of all possible sizes, it
is necessary to build the rollers always sufficiently high,
so that a sizing apparatus can be placed below them. There
must be also an elevating wheel, which carries the coarse
REDUCTION.
101
part back to the hopper. Often, depending upon the nature
of the ore or local arrangements, the different sizes obtained
are subjected to jigging or other concentratien, and the refuse
returned to the rolling mill, and sometimes this operation re-
peated two or three times.
In place of the lever, also springs are in use, wooden. India-
rubber, or steel. Steel springs are the most common. In
place of steel springs, in some places, India-rubber discs are
used of about one and a half inch thickness, eight inches
diameter, and six to ten in number.
All these contrivances for the sliding of the roller, and con-
sequently the long connection by tumbling shafts, could be
avoided by using belts in place of gear, so arranged that if
more power were required to overcome some obstruction the
belt would slide over the pully-face while the rollers stop.
The points which should be attended to in constructing a
crushing mill, are:
"First. To make all the parts sufficiently strong to
meet the varying resistances which continually occur
in crushing. For this purpose, the frame-work to receive the
rollers ought to be of good cast iron, the axles of the rollers
of the best wrought iron, and the cylinders of the hardest.
and most uniform metal.
Secondly. To design the machine so that the matter to
be crushed may be readily delivered into the hopper, sized
by circular sieves for the dressing process, and such portions
as are not properly crushed returned to the rollers without
the intervention of manual labor. In order to effect this,
the elevating wheel ought to be made of sufficient diameter
to allow the stuff, on being discharged, to descend by its own
gravity into the feed-hopper."
"Thirdly. To extend from the axis of the rollers long
tumbling shafts, and fix on their ends the driving wheels,
allowing a little play in the plummer blocks, so that any
undue opening of the rollers may not vary the pitch line of
the wheels to such an extent as to endanger the safety of the
teeth."
102
REDUCTION.
"Fourthly. To construct the rollers so that it may be
readily changed, yet maintained on its axis without slipping
when in motion."
((
Fifthly. The diameter of the rollers should be decreased
and the length increased in proportion to the fineness of the
stuff to be crushed, since a fine material requires a longer
line of contact, and not so large a grip as coarser sub-
stances.'
"" *
SEC. 26.
Feeding of Rollers.
The feeding of rollers is sometimes done by hand through
a small funnel, but generally by self-feeders, varying in their
construction. The most common is represented on Tab. II,
Fig. 12 side, Fig. 13 front view. The box, a, and feed-shoe,
b. are similar to those used in California for feeding stamps.
On the shoe there is an iron elbow, c, resting on the cam
teeth, d, of the roller, by which the feeding is effected.
A feeder of a different construction, used for smalls, is
shown by Fig. 6, Tab. VI, (A and B sections). The funnel
box, b, rests on a round one, c, in which there is an iron
scoop-wheel with twelve small buckets, a, which, revolving,
discharge the smalls through the spout, e, between the rollers.
The pulley, d, is driven by one of the rollers.
The crushed ore from the rollers falls on a sifting arrange-
ment, separating it generally into several sizes, the largest
part of which is delivered to jigging concentration. The
coarse stuff which does not suit for concentration is carried
back to the hopper either by an elevating wheel, or by scoop-
elevators. Inside of the iron rim are the buckets receiving
the smalls, and discharging when at the higher point, on a
platform or spout leading into the hopper. The wheels have
More common are the scoop-
generally a slow motion.
*Supplement to Ure's Dictionary.
REDUCTION.
103
elevators, after the plan used in flour mills. The scoops are
made sometimes of cast iron, but more usually of sheet iron,
which is preferable on account of being lighter. These
scoops, square or half round at the bottom, are fastened to an
endless chain of a peculiar construction. The rollers over
which this chain runs have a prismatic shape. More con-
venient, in place of chains, are India-rubber or leather belts,
to which the scoops are riveted.
SEC. 27.
Remarks.
In treating the ore by rollers it is important to have it
broken to a uniform size as nearly as possible, or to use
corrugated rollers as breakers for the next lower set. The
crushing of the smalls from jigging must be performed wet.
In this case water is conveyed into the hopper. In some
places, also, to avoid dusting and heating of the rollers, the
ore is crushed wet. Instead of the first set of rollers, stone-
breakers, with jaws, are much preferable, for the reason that
more uniform stuff can be obtained from them for the further
reduction, and because it often happens that the upper
rollers, in case of any obstruction, give way, when coarse,
unsuitable pieces, fall through. For this purpose, to catch
up such coarse stuff, complicated arrangements are invented
by which a trough is pushed under the rollers by the yielding
roller itself.
In some places stamps are employed to break large pieces
of ore preparatory for the rolling mill, but of late stone-
breakers, which prove to be very effective, are preferred
for this purpose.
At Charleston, in England, the ore charged on the rolling
mill is from four to five inches square; at Wheel Friendship.
of the size of a man's fist. At Alston Moor the ore is
crushed by means of three pairs of rollers; the upper set is
corrugated and crushes for the two next pairs on each side,
104
REDUCTION.
so that one part of the ore slides on an incline to one, and the
other part to the opposite pair of rollers.
In Hungary, it was found by experience that the rollers
work to better advantage if the ore is used in a damp con-
dition, broken to small pieces of one or one and a half inches
diameter, the rollers revolving sixteeen to twenty-two times
per minute, and the distance between them being kept less
than the required size of the ore particles. In other places,
again, the ore is dried before being delivered to the rolling
mill.
According to Philipps Darlington, the highest speed of
twenty-one rolling mills was one hundred and six feet, and
the smallest twenty-eight feet per minute; the average fifty-
four feet. The average of sixteen English rollers was 44.6
feet. They consider the best speed to be between forty-five
and sixty feet per minute.
The power required for a pair of rollers of a certain size
can not be found so easily by calculation, on account of the
unevenness of the ore and the uncertain position of a piece
at the crushing moment, as one and the same piece generally
breaks easier in one direction than in another. Besides this,
there enter into the calculatien many other complex circum-
stances in connection with the ore. At the Muldner Works,
Saxony, a pair of rollers, twenty-four inches in diameter and
eighteen wide, with eight to ten revolutions per minute,
crush, in twenty hours, ore, quartz, matte, etc., which is
charged in pieces of from two to three cubic inches,
three hundred to four hundred pounds weight to the size of
a pea and to dust, with six-horse power. At the Washington
Mine, Germany, the rolling mill crushes, in ten and a half
hours, of coarse spathic iron, blende and lead ores, two hundred
to two hundred and fifty pounds weight with ten-horse power.
At Cornwall one hundred and eight kil. of copper ore are
crushed with one-horse power, per hour.
from
REDUCTION.
105
SEC. 28.
Grinding.
Grinding differs in effect from stamping in producing more
fine powder by trituration. Grinding mills are the oldest.
means of pulverizing ores; the Romans used them, and sub-
sequently they were employed through all Europe in grind-
ing ores for the purpose of concentration. With the inven-
tion of stamps, by means of which a more effective crushing
was obtained, and one more suitable for concentration, grind-
ing mills were crowded out rapidly, and their use reduced to
pulverizing silver and gold ores for amalgamation.
Since the year 1860, however, after the discovery of silver
mines in Nevada, etc., grinding, combined with amalgamation
in iron grinding-pans, has come into very extensive use on
the Pacific coast.
All pulverizing machines agree in the principle of grinding,
yet the methods of doing it are so different that the modes of
construction became exceedingly numerous. As a means of
reduction for concentration, grinders are not to be considered
as proper contrivances, except in cases where the ore requires
to be reduced almost entirely to slimes; but the grinding-
pans are important in the dressing of ores, on account of the
immense quantity of tailings turned out by them, which must
be considered in connection with concentration.
1. The Arastra or Tehana is one of the primitive grinding
arrangements. It is still extensively used in Mexico and
South America, and to some extent in California. Because
of its cheap and simple construction, the arastra is very
often the pioneer of machinery in gold mines situated in re-
mote mountainous places. Grinding and amalgamation is
always combined if there is fine gold in the rock. Silver
ores are ground to an impalpable powder or slime, called
lama," and treated subsequently by amalgamation in heaps,
(patio amalgamation).
8
106
REDUCTION.
The arastra consists of a circular excavation, the bottom
of which is paved with some kind of hard and tough rock, as
granite, greenstone, porphyry or basaltic rock. In putting
up an arastra, a wooden post is first driven in the centre of
the circle into the ground, twelve to fifteen inches of it pro-
jecting above the intended pavement, and is constructed
either of stone or wooden staves. Four stones of large size
are laid in the form of a cross on the bottom, all four per-
fectly level. They serve as guide stones for the paving.
The spaces between the large stones are filled up with
smaller ones, set perpendicular to the long axis. In some
places stones are selected of an oblong shape, and set verti-
cally. The surface of a new bottom is very rough. For
this reason it must be covered with sand or rubbish, so that
the grinders can be dragged over it without obstruction.
Into the post an iron box or bearing is inserted, for the
reception of the pivot of an iron or wooden shaft. Through
the wooden shaft two or four arms are fitted crosswise, to
which four large stones are attached by strips of rawhides,
ropes or chaius. For this purpose two holes are drilled into
each grinding stone, and plugged up with wooden plugs, to
which the chain is fastened. The grinders must run for six
or twelve hours with sand, in order to fill up all spaces and
wear off the roughest projections before the ore is charged.
The diameter of an arastra is from six to sixteen feet,
requiring proportionately four to eight grinding stones. The
shaft, if driven by water or steam, revolves from eight to ten
times per minute. One arastra can grind from one to two
tons in twenty-four hours; but not more than six to eight
hundred pounds in the same time if worked by horse or mule
power. The weight of the grinding stones is from six to
seven hundred pounds.
In treating gold ores, the quicksilver finds its way down
under the pavement, and the amalgam gets into the crev-
ices, so that, in cleaning up, a portion of the quicksilver and
amalgam always remains between and below the rocks, unless
the whole of the stone bottom is taken out. To avoid the
REDUCTION.
107
troublesome refitting, iron pans are sometimes used, lined
with regularly cut stones, which, if taken out for the purpose
of cleaning, can be easily replaced in the same position.
Arastras are always built so that the lama or ground stuff
can be discharged by opening a gate, which is closed by sev-
eral horizontal plugs of a square section; and, in case gold
ores are ground, a continual stream of water carries out the
tailings over the plugs, which are removed by degrees. Ore
ground without amalgamation is discharged at once by open-
ing the slide-gate. In charging arastras in California, the
ore is frequently broken to pieces of the size of a hen's egg;
in Mexico, generally smaller. It is more advantageous for
the grinding to charge at first only a hundred and fifty
pounds of ore with sufficient water, and to add another
charge after two or three hours' run.
2. The Edge, or Chili Mill.-These mills are used not only
for ores, but also in manufactories for grinding different arti-
cles; also for cement, slag and rock grinding. The construc-
tion varies, but is founded on the same principle. The
runner or grinder is generally a roller of a larger diameter
than its face, sometimes of a conical shape, corresponding
with the circle it has to describe. The runner, with a hori-
zontal shaft, rolls in a vertical position on the outer circum-
ference of a flat or slightly conical basin, crushing more than
grinding. The runners are sometimes made of stone, some-
times of cast-iron. The basin is either paved with stone or
iron plates, or, if of a small size, the iron runners roll in iron
pans. Some mills are so constructed that one roller, usually
the heavier, is nearer to the upright shaft than the other.
In other cases, the horizontal axis of the runners is fixed, and
the pan revolves. The usual speed is from six to ten revolu
tions; the diameter of the runners from three to six feet.
The ore must be broken small, and charged in small portions.
The capacity of Chili mills is limited, both as to quantity of
grinding and amalgamation. Several mills in California had
formerly six to ten iron Chili mills, receiving the crushed ore
108
REDUCTION.
from the batteries. Each mill was charged with twenty to
fifty pounds of quicksilver, but the amalgamation was not
satisfactory.
To this class of mills belong also Hall's Dry Pulverizer and
the "Little Giant."
Hall's Pulverizer is a combination of the Chili mill wheels
and the arastra grinder in a cast-iron pan. The pulverizing
surfaces of wheels and arastra are somewhat convex, run-
ning in a concave annular trough. The pan is air-tight,
covered with sheet-iron. and is connected with a blower.
The air passes through a table, and enters a pipe, which
surrounds the lower part of the pan. From the pipe there
are forty five-eighth inch holes leading into the pan, directly
under the crushing wheels, which deliver the air in jets,
stirring up the ore constantly, and keeping the coarse sepa-
rated from the fine powder, which is carried out through a
spout. The receiver must be in the shape of a dust chamber.
The "Little Giant," also a dry pulverizer, is constructed on
the principle of a Chili mill, with stationary wheel axles and
revolving bottom, which communicates the motion to the
wheels, of which there are four in number.
Next to the Chilian mills are the
3. Ball Mills.-In place of the runners or wheels described
there are sometimes iron balls, two in number, from ten
to fifteen inches diameter, rolling in an annular concave
basin, each ball driven by two pins from the horizontal arms
of the upright revolving shaft. These mills have been also
used for grinding and amalgamating purposes in California,
but with no better results than the Chili mills. A different
arrangement from this are the ball grinders, in shape of
cylinders revolving on horizontal shafts. They are made of
wood or sheet-iron, and contain from six to eight balls from
six to eight pounds in weight. By means of the balls the
stuff is powdered during the revolution, and, when sufficiently
fine, discharged through a hole, closed by grates, which pre-
vent the balls from falling out. These grinders are used for
REDUCTION.
109
pulverizing gypsum. A successful application of this mode
of grinding is
Lundgren's Pulverizer, which differs from the preceding,
principally in the size and number of the balls employed.
The drum is made of boiler-iron. The shaft, to which the
drum is fastened by flanges, is three and a half inches in
diameter. On the circumference of the cylinder, which is
five feet long and five feet in diameter, there is an aperture,
provided with a coarse sieve, for the discharge. The bullets
are cast of white iron, and are five-eighths of an inch in
diameter. The drum is charged first with two thousand four
hundred pounds of these bullets, and then with eight hun-
dred pounds of ore, which has been previously reduced to a
coarse powder, such as can pass through a sieve of about
twenty-four meshes to the running inch. After two or three
hours' motion, (twenty-four to twenty-six revolutions per
minute) the ore is perfectly pulverized, suitable for amalga-
mation. The proper speed is essential; too slow or too fast
causes imperfect or too slow grinding. One of these
machines is in operation in Bear Valley, Mariposa county,
California. The ore is first reduced by a stone-breaker
(Blake's, $16, B) to the size of a walnut. From this it drops
between two Cornish rollers, and then on a sifting apparatus.
What falls through a screen of twenty-four holes to an inch
is passed to the ball cylinder. In case the boiler iron should
wear too fast, the machine could be furnished with shoes.
This pulverizer seems to be most suitable for grinding
roasted ores for the barrel amalgamation. The pulverization
of roasted ore, before it is subjected to amalgamation in
barrels, is indispensable for a good result, and this has been
the greatest objection to the barrel process; so that in many
instances on this account pan amalgamation has been pre-
ferred to barrels, which, in other respects, are more advanta-
geous. An iron pan grinds and amalgamates at the same
time. This cannot be done in a wooden barrel; and the
experiment of amalgamating in iron barrels with iron balls
·
110
REDUCTION.
did not answer. On the other hand, the use of horizontal
mill-stones is expensive, slow, and, in most districts, difficult
to apply. In these, as in common with iron grinders of a
similar construction, the troublesome sifting cannot be
avoided, while the pulverizer just described, grinds a con-
siderable quantity in a comparatively short time without the
least dusting, except at the discharge; and as the charge
and discharge is not continual, the fineness of the grinding
can be regulated as may be required for amalgamation with-
out sifting.
There are many differently constructed ball grinders and
amalgamators. As grinders, they are not very effective, and
as amalgamators, entirely inadequate.
4. Cylinder Mills.-There is a variety of this class of
grinding mills, the principle of which lies in the friction or
grinding of the cylindrical mantle against a stationary con-
cave surface. The motion of the cylinders is either revolving
or oscillating. The outlines of Fig. 19, Tab. II, represent
two rollers, a, a, grinding against the surface, b, which is
adjustable by screws from below, so that it can be brought
close to the rollers.
Another construction is that of Collyer, for grinding and
amalgamating. A large drum is filled with rock, weighing
about ten tons, and has a revolving motion, while a smaller
drum, connected with the first by an iron rod, oscillates.
The ore, in small pieces, is charged in a trough under the
revolving drum, passes on the other side, through a vertical
sieve, into another smaller trough of the oscillating drum,
and is discharged, through a sieve, into an amalgamator.
Farrand's Oscillating Amalgamator belongs also to this
class of grinders. There is a semi-cylindrical trough-shaped
iron box, furnished on the interior with dies. The muller is
convex, provided with shoes, and attached to a substantial
oscillating shaft, moved by a crank.
Another construction of a cylinder grinder is Hopkin's
REDUCTION.
111
Cylinder Amalgamator—a cylindrical pan, provided on its
inner surface with dies, extending the whole length of the
cylinder. The pan has a flange, to which a cover is secured
by bolts. Within the pan, secured to the horizontal shaft, is
a muller, with grinding shoes. The muller may be described
as a part of a cylinder, cut off obliquely, and secured to the
shaft, from which the face of the muller is at all points
equally distant and parallel. The shoes are curved, to cor-
respond with the dies, and when secured to the muller
extend over the whole interior length of the cylinder. The
horizontal shaft carrying the muller is supported in self-
adjustable metallic boxes, having a sufficient amount of
vertical play, and so constructed that they thoroughly pro-
tect the journals from sand. The pressure of the muller is
regulated by rod set-screws at one end, placed below and
supporting the boxes to the extent necessary. The rods of
the set-screws are acted upon at the same time, through
bevel gears, by a shaft.
The grinding surface of a thirty-six-inch muller is seven-
teen square feet, and it is said to be capable of working one
thousand eight hundred pounds of ore at one charge. The
shoes and dies are easily replaced when worn out.
5. Horizontal Mills.-The oldest mills of this kind for
grinding ores which are still in use, are the horizontal stone
mills. Where dry crushing is essential-for instance, with
roasted ores, matte, black copper, etc.-these grindstones.
answer perfectly in regard to quality of the ground stuff;
but in some localities they are expensive, require dressing
about twice a week, and the runner wears out in a few
months. Still they are considered as among the best dry
grinders. The mill consists of two circular flat stones, one of
which is the stationary bed-stone, the other the revolving
runner. The runner has a feed-hole in the centre, and is
generally thicker than the bed-stone. The surface of the
runner is in contact with the bed-stone from the periphery
to within one inch of its diameter. The surface of the run-
112
REDUCTION.
ner then runs towards the centre, in order to receive the
stuff freely.
The following particulars wiil convey practical information
relative to a horizontal stone mill:
Diameter of stones..
Thickness of bed-stone.
4 feet 2 inches.
•
·
12 inches.
Thickness of runner..
Number of revolutions per minute.
Gauge of stuff in the hopper.
Gauge of stuff on delivery.
• •
•
Quantity of stuff ground per 10 hours.
Power employed...
Character of runner.
Character of bed-stone.
•
·
Duration of the runner.
Duration of the bed-stone.
every third day.*
•
• •
•
•
D
·
•
14 inches.
108.
100 holes to the square inch.
.3,600 holes to the square inch.
1 ton per pair of stones.
. about 5-horse.
.. coarse conglomerate.
·
compact stone, moderately hard.
18 weeks (average).
.22 weeks (average), when dressed
The surface of the bed-stone is sometimes now, and was in
early times, concave; that of the runner, convex. There
are many different iron dry grinders constructed on the prin-
ciple of horizontal mills, which grind very effectively; but
when the shoes of the runner become smooth, they must be
renewed, as well as the dies; while the stone is dressed up
and used again, until unfit by its reduced weight for further
use. The best iron grinders for dry grinding seem to be
those with cast-iron dies, the radial grooves of which are
tightly fitted with wrought-iron or hard wood.
Bogardus first constructed a mill, in which the runner was
placed upon the bed-stone in an eccentric position. The
bed-stone, or disc, provided with a die of white-iron, the
grinding surface of which has spiral ribs, is connected with
the driving shaft, representing thus the runner. The upper
disc has shoes with spiral ribs, the curve of which is reverse
to those of the lower. The upper rests on the bed-plate,
with a certain distance between the centres. Its bottom
throat, representing the feed-hole, is suspended in a collar
fixed to the cover. The motion of the bed-plate imparts
motion to the upper one by friction. The mill, although
highly satisfactory for different grinding purposes, did not
give a good result in pulverizing ores.
*Supplement to Ure's Dictionary.
REDUCTION.
113
SEC. 29.
Iron Pan Grinders.
These grinders are also amalgamators; consequently wet
grinders. Almost all of them work upon a charge of ore a
certain length of time, and not with constant feeding. Orig
inally, they followed the principle of the arastra and hori-
zontal mill; but, in course of time, besides the horizontal
grinding surfaces, also conical ones, etc., were adopted, and
thus the pan grinders gradually became divided into four
different classes-First, pans with plane, circular; second,
with conical; third, with tractory conoidal; and fourth, with
vertical mullers.
It seems evident that in a pan with a circular plane bot-
tom the grinding must increase from the centre towards the
periphery, as each point of the muller on a radial line
describes a larger grinding circle in proportion as it is fur-
ther from the centre; consequently each point must pulverize
a greater amount of the ore than points nearer to the centre,
and wear in proportion. If, on this account, the muller
wears sooner on the periphery, a partial suspension of work
seems to ensue, so to say, the points near the circumference
waiting until the wear towards the centre overtakes that on
the periphery. It seems, then, conclusive, that if muller and
dies could be constructed of a material continually increasing
in hardness towards the periphery, the grinding and wear
would be rendered uniform.
This calculation on grinding is derived directly from that
treating the friction of plates and pivots. It would answer
also for grinding, provided all points between the grinding
surfaces had an equal layer of the stuff to be ground-that
is, in proportion-so that, for instance, a grinding area of one
hundred square inches near the centre had to grind ten times
less than a thousand square inches towards the periphery.
This, however, is not the case. It is certain that a definite
114
REDUCTION.
quantity of ore entering continually under the muller through
the annular opening near the centre of say 3.14 feet circum-
ference, will be discharged from a grinding surface of 18.84
feet circumference (at six feet diameter).
It is evident that the quantity of quartz which enters the
central opening must decrease in proportion as it moves
towards the periphery—that is, in reference to the increasing
grinding surface of the muller. Besides this dilution or
spreading, the quartz is being ground on its way towards the
periphery, which receives not only six times less quartz than
the central opening, (in reference to the six times larger
circle) but also already ground to some extent. It is there-
fore plain that the wear of the muller has a tendency, from
this cause, to decrease towards the periphery. Again it is
certainly necessary to consider also the radial slots between
the shoes of the muller, by which the grinding surface far-
ther from the center is supplied with fresh stuff. But this is
modified, as the sectional size of the slots decreases by the
wear of the shoes, and their being also choked up by amal-
gam and other matter.
SEC. 30.
Pans with Plane Circular Mullers.
These grinding pans, of which there are many in success-
ful operation, are constructed after the arastra plan. The
improved ones correspond with the horizontal stone mills.
A. The Common Pan is a flat-bottomed circular pan, of
from four to seven feet diameter. In order to save the pan
bottom from wear, there is a false bottom, generally in one
piece, the center of which has a hole corresponding with the
cone of the pan. The bottom disc, two inches thick, is fast-
ened only by wooden wedges around the periphery and
around the cone. If also amalgamation is intended, the
REDUCTION.
115
wedging must be performed very tightly, so that no quick-
silver may penetrate underneath the plate. Two parts of
iron filings with one part of clay and strong vinegar is a good
cement for this purpose. Through the cone projects the
driving shaft, to which the yoke is fastened. This yoke has
two arms, which fit into two holes of a wooden or iron cross, to
which the shoes are attached by bolts. The space between
the shoe and cross is filled with wooden blocks of the shape
of the shoe. These mullers revolve from ten to twelve times
per minute.
The pan is charged when the muller is in motion, first with
water and then with from one hundred and fifty to three
hundred pounds of ore. The grinding capacity of these
pans is insignificant. For this reason the ore must be pul-
verized beforehand to the size of one-sixteenth of an inch at
least.
B. The Tub Grinder and Amalgamator does not differ
from the common pan materially. The construction is the
same. There is an iron bottom, with wooden stave sides of
twelve to fifteen inches height.
C. The Bartolo Pan is a common iron pan, of smaller size,
with two shoes. All pans of a like construction are now
very little in use, excepting to grind rich residues and to
unite and clean the amalgam received from settlers and pans.
D.
The Knox Pan, for grinding and amalgamating, is like
the common pan, with a flat bottom; but, in place of the
arastra grinders, there is a grinding-plate, in the shape of a
curved cross, forming four arms. This pan is preferred by
many millmen, who consider the slow amalgamation of gold
more profitable. In treating gold or silver ores, there is a
wooden stationary frame above the muller, coated with amal-
gamated copper-plates. The outlet is in the cone. The
pulp is discharged where there is the least motion, in order
to prevent the escape of fine gold or granulated mercury.
116
REDUCTION.
There is also a patent steam chamber below the bottom of
the pan. The treatment of Knox's pan is like that of a com-
mon pan. The ore is charged when the muller is in motion
after water has been introduced, and the steam-cock opened
to let sufficient steam in the chamber to heat the pulp.
After four or six hours, according to the nature of the ore,
the pan is filled with water, and allowed to run for fifteen or
thirty minutes, and then discharged.
E. Varney's Pun.-This pan is one of the best grinders
and amalgamators, and very extensively in use. The pan is
constructed after the principle of the "horizontal stone
mills." The bottom is formed by four dies of white cast-
iron. Each die has a countersink, for the reception of a
bolt, by which it is fastened to the bottom of the pan. The
die has two radial grooves, and does not join the next die, so
that other grooves are formed between the dies. According
to Varney, the grinding capacity of the pan is greatly
increased by filling these grooves tightly with hard wood.
The annular space between dies and cone is filled with
cement or wood. There are twelve shoes, riveted or bolted
to the muller. The muller is separate from the hub, which
forms a cone, covering the pan cone. It has two projections
at the base, by which the motion is imparted to the muller.
The hub is fastened to the vertical shaft by a set-screw and
key. The gear, in which the shaft can slide up and down,
rests on a two-legged chair or support, which is bolted to a
cross, and this again to the four legs of the pan.
In putting up this pan, the cross must be bolted first firmly
to the legs; the lever and step-box put in its place; the
chair bolted to the cross, and the gear-wheel placed on it.
The top of the legs should be leveled, and the pan, with its
corresponding projections, set on them. The shaft is then
put in its place, and the pan or step-box moved until it is
perpendicular. For this purpose the step-box has sufficient
play in the box of the cross. Some fine cement or soft clay
must be equally spread over the bottom of the pan, and the
REDUCTION.
117
dies put in, with the bolts through them. Between the peri-
phery of the dies and the pan four wedges are driven, each
wedge pressing against the corners of two dies, and so
driven as to make the space between the edge of the dies and
the pan equal all round. First a rubber, then an iron washer
is placed on the bolts under the pan; then the nuts screwed
on, and the dies drawn as close to the bottom of the pan as
possible, taking care to keep them perfectly level on their
upper surface.
The radial slots in and between the dies are filled with
hard wood, driven endways; also the space around the cone
as thick as the dies. The wedges can be removed now. A
tram is put on the vertical shaft, and the lower box moved
until it is perpendicular with the dies; then the box bolted
to the cross. The driving shaft must be leveled, put in line,
and the driving gear put on, etc. After this, the hub is
placed on the vertical shaft, and then the muller in its place.
The hub must be raised now, and fastened with the set-
screws to the shaft. As the dies wear down, the hub can be
occasionally lowered on the shaft, so as to keep the top of the
box about level with the cross. The guide-plates are put in
the pan, bolted fast to a ring, and the pan covered. A hand-
wheel is put on the rod, and the guide-plates raised, so as to
clear the muller.
By aid of a lever, the muller can be perfectly regulated, so
as to grind not at all, or only partially, or with its full force.
Always before the start (of the whole set) the mullers must
be raised. When in motion at the rate of between eighty
and one hundred revolutions per minute, and after sufficient
water has been introduced, the ore can be charged with the
shovel. From six to eight hundred pounds constitute a
charge. Coarse stuff, as obtained from sifting, with screens
of about four meshes to the inch, or coarser, is ground better
if the muller is lowered by degrees. The rapid motion
throws the ore towards the side of the pan. In order to
change the current, there are the curved plates, which guide
the stuff back to the centre and under the muller. A charge
118
REDUCTION.
of coarse ore is ground perfectly fine in about four hours.
Finer stuff, as usually charged for amalgamation, turns into
a fine pulp in less than two hours. The pulp must be kept
diluted so much that a swift motion of it around and behind
the guide-plates can be observed.
For the purpose of heating the pulp, there is no steam
chamber in Varney's pan. The steam (for amalgamation) is
introduced through a steam pipe above the muller directly
into the ore. There is really no reason for a steam chamber
which consumes more steam.
Varney's pan is generally charged with eight hundred
pounds of crushed ore, and revolves eighty times per minute.
It requires from three to five horse-power. With new shoes
on the muller, and grinding with the full weight, it takes a
good deal of power on coarser sand, especially in the begin-
ning; but the effect is in proportion. Eight hundred pounds.
of sand, through No. 4 sieves, are ground exceedingly fine in
two or three hours. Shoes and dies wear out in from forty
to sixty days' run of twenty-four hours.
Constant good working of these and similar pans depends
on keeping them constantly in perfect order. The part most
frequently neglected is the oiling of the box of the pan cone
and the part of the chair upon which the gear runs. This
happens in consequence of not keeping clean the top of the
hub, from which the oil passes through an oil hole into the
box and down on the chair. The Babbett metal soon wears
on one side, the shaft plays loose, comes out of the perpen-
dicular line, and the muller runs unevenly, causing very bad
wear of shoes and dies. There are mills in Mexico, and also
in California, where Varney's, Hepburn's, and other pans,
after one or two years' use, can be seen in a horrible condi-
tion. The advice cannot be repeated too often to repair
any part of the machinery which gets out of order without
delay, no matter whether it could run a day or two longer or
not. One evil creates generally several others.
F.
:
Wheeler's Pan.-Figs. 1 and 2, Tab. III, shows one of
REDUCTION.
119
Wheeler's improved pans. Fig. 1, is a cross section on the
line, z, of the ground view, Fig. 2, of which one part exposes
the dies. The other part shows the muller with shoes, the
latter indicated by dotted lines. There are many valuable
improvements made on the old Wheeler pan. A particular
description is not required; the general arrangement is
easily understood. Most of the new pans have a cross-piece,
m, on which the box, "", for the horizontal shaft, r, the step-
box, p, and the lever, q, are fixed, varying only in shape and
arrangement. The lever, if screwed up by the hand-wheel,
lifts, by means of the pin, v, the box, and with it the perpen-
dicular shaft and muller. The upright shaft, h, is provided
with a screw, u, on which the muller is screwed up so high
above the rim of the pan that cleaning or changing of dies
can be performed conveniently. The hoisting apparatus is
avoided by this arrangement. The guide-plate, i, or, as it is
improperly called, "scraper," of which there are four in a
pan, is short. It gives to the moving pulp sufficient direc-
tion towards the centre. They are readily removed from
the t-shaped projection of the pan. o, is a pipe conveying
oil to the box on which the hub of the gear, k, runs.
shows the steam chamber for heating the pulp. The muller,
f, is provided with two openings, b, b, for the reception of the
dove-tailed projections of each shoe, as represented in Fig.
3, Tab. III. This is a very simple mode of fastening the
shoe, e, to the muller, f. c, is a vertical section of e, on the
line, a. The shoe is placed under the muller, so that the
projections, b, b, fall into the corresponding openings of the
muller. The space, k, is then filled by a wooden wedge, and
the shoe stands firm. The dies, a, Fig. 2, of which there are
four to each pan, have a similar dove-tailed knob, which is
wedged into a corresponding recess in the bottom of the pan.
2,
In order to impart a rising current to the stuff on the peri-
phery of the bottom, there are inclined ledges, 7, on the sides
of the pan. Smaller ledges, l', are on the periphery of the
muller, for the same purpose, but inversely inclined. The
space, a', between the dies, can be wedged with hard wood,
after Varney's plan.
120
REDUCTION.
The grinding operation, as well as the amalgamation, does
not differ from other pans. One charge consists of from six
to eight hundred pounds.
G. Union Grinder and Amalgamator.-This pan is a very
efficient grinder, of a peculiar construction. It has double
grinding surfaces—that is, two sets of shoes, revolving in
opposite directions, by which arrangement they have a
grinding surface between themselves, while the lower set
also acts upon the dies affixed as usual in the bottom of the
pan. The shoes are attached to the arm by a ball and
socket, or rolling joint, by means of which the shoe is made
to bear equally at all times upon its work, and conform itself
to the equal labor between the centre and outer portions of
the pan bottom.
The double action of the mullers produces an agitation of
the pulp, which takes the form of a series of eddies, at inter-
vals around the shaft and about half way to the circumfer-
ence of the pan. This peculiar agitation causes a rapid
movement of the pulp from the bottom to the surface, and
vice versa, passing and repassing it constantly between the
grinding surfaces, and producing a frictional current over
the mercury at the periphery of the pan.
H. Moore's Quartz Grinder and Amalgamator.—This is
a very simply-constructed machine, used in several mills of
California with great satisfaction. It is a flat-bottom pan,
furnished, as usual, with dies and a heavy muller, with
shoes, the pan being six feet in diameter. Around the cone
there are conical crushing-plates, against which the corres-
ponding vertical shoes of the neck or collar of the muller
grind. The collar widens at the top, funnel-like, for the
reception of the crushed ore, which continually flows in from
a five-stamp battery. The ore is thus partially ground in its
vertical descent before it enters the horizontal grinding sur-
face.
It is claimed that five stamps, five hundred pounds each,
REDUCTION.
121
and two grinders, will reduce twenty tons of gold rock per
twenty-four hours, with a twelve-horse power engine, to a
very fine powder, suitable for any kind of amalgamation.
Gaston's Grinder and Amalgamator.-The muller of this
pan consists of a screw, with four broad flanges, or threads,
similar to a propeller screw, which flanges overlap each other
a short distance, to permit and compel a free passage of the
pulp between them. The screw is about three feet in diam-
eter, and revolves horizontally within a low, vertical cylin-
der, and the shoes for grinding are attached to the base of
flanges or threads. Through the base of the cylinder are
oblong holes or spaces, corresponding in size and number to
the spaces between the threads of the screw. These permit
the pulp to pass out from or into the cylinder. The revolu-
tion of the screw in either direction causes the pulp to flow
to the centre of the pan, and forces it between the shoes and
the dies, thus adding the force of the screw to that of grav-
ity when rotated in one direction, and forcing to its aid an
atmospheric pressure when revolving in the opposite direc-
tion.
SEC. 31.
Pans with Conical Mullers.
A. Hepburn & Peterson's Pan.—This pan has a conical
bottom, with the greater base upwards. The bottom inclines
towards the center at about twenty-eight degrees from the
horizontal line. There are four dies on the bottom, placed so
that the legs on them fit into corresponding recesses of the
bottom, wedged by a piece of wood. There is no space left
between the dies. The grinding surface appears compact.
The dies are easily removed and replaced when worn by use.
There is a cone, or tube, in the centre of the pan, through
which the shaft passes. The tube does not require to be
higher than the rim, as the pulp assumes a conical shape,
9
122
REDUCTION.
being quite low at the centre, when the muller is in motion,
with a speed of from sixty to seventy revolutions per minute.
One charge takes one thousand pounds of ore.
The muller corresponds with the conical shape of the pan
bottom. It has an upright hollow tube, diverging into four
standers, where it is attached to the muller. The hub has
at the base three projections, which are placed in the corres-
ponding openings of the tube and turned to the right. The
knobs of the hub stand under leveling screws. A hand-
wheel serves for raising the muller, which can also be per-
formed during the motion by arresting another wheel. The
shoes are attached to the underside of the muller by bolts.
The edges of the shoes are beveled, so that an oblique groove
is formed between each two. When the shoes are worn, the
groove gets so small that the passage of the pulp is consid-
erably hindered. For this reason the muller contains also
radial grooves between the shoes, which allow the ore to
pass, even when the shoes wear to one-fourth of an inch.
The pulp stands on the periphery higher than at the cen.
tre, and the conical shape of the bottom causes it to move
constantly from the sides down to the center in a spiral
way, so that no guide-plates are required. In many mills,
however, three or four small scrapers are attached to the
side of the pan. This peculiar motion admits the pulp being
kept quite thick, almost as the ore should be kept in bar-
rels-a valuable property for amalgamation of roasted silver
ores.
B. Belden's Pan.-The shape of the bottom in this pan is
also conical, but unlike Hepburn's, with the greater base
down and less inclined. The grinding and amalgamating
capacity is like that of other first-class pans. The construc-
tion is similar in other respects to other grinding pans.
C. Baux & Guiod's Grinder and Amalgamator, having a
slightly conical grinding surface, with the greater base
down, belongs also to this class of grinders. The muller
REDUCTION.
123
consists of four flat curved arms, to which the shoes are
attached. The dies ascend towards the centre, where the
refuse or ground stuff is carried out, the pan being closely
covered. The principle is similar to that of Varney's old
" continual."
The feeding with Baux's amalgamator is continual. The
stuff (from a battery) is conveyed into a spout, which com-
municates with the inside of the pan on a periphery. The
pressure in the spout forces the pulp to rise and to come out
at the centre around the hub. Baux & Guiod's pans are
adopted in many mills, and give, with free gold, satisfactory
results, which, however, depend on the mode of working.
The pressure in the spout must be small, so that the feeding
shall be slow. One ton in twenty-four hours will give a
much better result than two; but three tons is altogether
too much.
In regard to silver ores, generally speaking, no " contin-
ual" will answer, for the simple fact that the silver mineral
must be decomposed before it can be amalgamated, requiring
for this process time, which is not afforded with constant
feeding. It is stated that Baux's pan, treating roasted silver
ore, gave a better result than the barrel, operating on another
portion of the same ore. This gives credit to the pan, but
certainly a good deal more blame to the operator with the
barrel, who did not understand the process he had under-
taken to carry out.
SEC. 32.
Pans with Tractory Conoidal Mullers.
A. Excelsior Pan.-This grinding and amalgamating pan,
constructed by Wheeler & Randall, differs materially from
others, in having a conoid in the centre, whose greater base
reaches the periphery of the bottom; that is to say, the
pan-side at the bottom, changes, directly ascending with
124
REDUCTION.
the conoid. The larger base is, therefore, nearly equal in
size to the diameter of the pan bottom. The shape of
muller shoes and dies corresponds with the conoid. Shoes
and dies are fastened simply by wooden wedges, as described
in Wheeler's pan. The guide-plates have an inclined posi-
tion in the direction of the moving pulp, by which less
obstruction is offered to the stuff in motion. The perpen-
dicular and horizontal shafts, the gear, step-box, lever, etc.,
are similarly constructed as in Wheeler's pan. The muller
has openings between the shoes, so that the pulp has per-
fectly free access under the full face of the shoe. This
construction contributes greatly to the efficient grinding of
the pan.
The Excelsior pans are made at the Union Foundry, San
Francisco, in different sizes. The largest pan measures four
feet diameter on the base of the muller, capable of reducing
one ton and a half of ore at a time. These pans are excellent
grinders. As to the size, the opinions of millmen do not
agree. It cannot be denied that using one large pan in place
of four smaller ones, giving four times as much time for
amalgamation and grinding of the same quantity of ore, the
wastage of ore, quicksilver, time, labor, etc., will be greater
with the small charges. The reduction of silver ores-that
is, the decomposition of sulphurets or chlorides-requires a
certain time, independent of the quantity; and in this
respect, eight hours' amalgamation in a large pan, with a
heavy charge, will be, proportionately, more effective than
smaller lots in shorter time. Besides this, there is less room
required for a large pan, less machinery, and less attendance.
The attention of the person in charge is more concentrated,
etc. On the other hand, there is the objection that the
advantage of large pans is limited, as the time of grinding is
not in proportion with the quantity of ore used, and that a
certain part of the stuff, the amalgamation and grinding of
which is finished, will be ground over and over again, use-
lessly, a great deal more in a large pan than in a smaller one,
and, consequently, that more loss in quicksilver will ensue.
REDUCTION.
125
This last objection, however, seems not to be well founded,
inasmuch as the mercury in four smaller pans is exposed to
grinding under a much larger grinding surface, although for
a shorter time.
B. Wheeler & Randall's Pan.—This pan differs from the
Excelsior in having the greater base of the conoidal muller
turned upwards. By this arrangement the grinding surface
is further off from the centre, requiring, on this account,
more power. There is a steam chamber with the pan.
These pans are in favor in mills where they are employed.
C. Excelsior Continuous Grinder.-The object of this
grinder is, like Baux & Guiod's, to grind or regrind such
stuff as may yield some metal by being further pulzerized
under continuous discharge. The inner construction does
not differ much from the Excelsior pan. Between the flanges
of the pan and cover, a rubber or other packing is applied to
make the joint water-tight. The upper part of the cover is
open. The pan is fed by a spout, with some little pressure,
and the discharge goes over the cover. This continuous
grinder is an effective grinder and amalgamater, especially
for material containing gold, but more particularly for amal-
gamation as an auxiliary machine, receiving the tailings in a
constant uniform stream.
A grinding pan, which is at the same time an amalgamator,
will give always a better result, if the charge can be worked
as long as the character of the ore may require. A continual
discharge is independent of the work which ought to be
done. The time of amalgamation and grinding depends on
the continual feeding, speed of the runner, and quantity of
water used. For this reason continual feeding ought not to
be used with silver ores. Both roasted and unroasted silver
ores require time for the decomposition of the silver com-
binations. But even for the collection of gold or amalgam
particles, the continually discharging pans will give a satis-
factory result only by feeding with a sufficiently diluted
small stream, and with a moderate speed of the muller.
126
REDUCTION.
SEC. 33.
Pans with Perpendicular Mullers.
The Centrifugal Ore Grinder. This grinder and amal-
gamator (Hinkle & Capp's) is of a singular construction. The
grinding is effected by perpendicular mullers, pressed laterally
by centrifugal force against perpendicular dies fitted to the
inner sides of the pan. It is to be run at a speed of from
sixty to eighty revolutions per minute, according to the
hardness of the rock to be crushed. The pressure upon
every part of the grinding surface is direct, increasing
towards the heel of the muller, so that the pulp enters
readily between the mullers and side dies. The wear is
represented to be only on the grinding surfaces, and the
work performed without jarring, jerking, straining, or
clogging, and with regularity and evenness. A piece of iron
or rock, which might be accidentally introduced with the
ore, will not cause a breakage or interfere with the grinding,
if between muller and die, as the former can readily pass
over the obstruction.
The pan is easily cleaned up, as each muller can be lifted
out separately by hand, and there is no necessity for lifting
the revolving cone or driver, which is easily turned, there
being no friction when not in use or rapid revolution. The
side dies are also readily removed when worn out.
ore.
This pan takes charges of about eight hundred pounds of
The cone at the bottom branches into six arms, on
which the hangers are hinged loosely, playing freely on pins
near the ends of the driving arms, and also supported by
having each a projecting lip, which rests on a bearing surface
on the arm which follows it. These hangers carry the muller
plates or shoes, kept parallel to the dies on the side of the
pan. Round the cone is a circular funnel-like feeder con-
veying the ore towards the bottom.
REDUCTION.
127
The mullers weigh forty pounds each, and the armed pan,
including six extra mullers, three thousand pounds.
This pan is also arranged for a continuous grinding, being,
then, three hundred pounds lighter.
In conclusion, is to be mentioned yet the recent inven-
tion of
Varney's Quartz Grinder.*-This grinder, as far as its effici-
ciency for production of the finest flour is demonstrated by
actual work, is one of the most important contrivances for
gold and silver metallurgy. The extensive patio operations
of Mexico and South America, the chlorination of gold and
silver ores, the silver precipitating processes and barrel
amalgamation, depend in the results very much on a fine pul-
verization.
The machine grinds from four to five tons of ore in twenty-
four hours. The quartz must be broken small by a rock-
breaker or other means before being introduced into the
grinder, which is permanently fed by a hopper. The machine
consists of two conical grinders, with their bases downwards.
The upper one is stationary, and the lower one revolves, and
is adjustable vertically. The grinding surfaces do not come
together, except at the periphery, from which point they
gradually separate, until at the top they are far enough apart
to receive the material to be ground, which may be such as
would pass through holes from one-fourth to three-fourths of
an inch diameter.
The shoes and dies are not ribbed or corrugated, but
smooth. The grinding effect, thorefore, will likely be the
same as long as the dies last. Between the dies are slots
transverse to the line of motion, filled with wood. The
wood being softer than the iron, keeps worn slightly below
the surface of the iron, leaving a shallow groove along the
face of the wood, down which the ore passes, until it is
*The drawing of the grinder could not be taken up in this book, as all the
tables were printed before the effectiveness of the machine was proven.
128
REDUCTION.
•
caught by the opposite surface and further reduced. A
peculiarity of this groove is, that as it is formed by the natu-
ral action of the rock, which is coarse above and fine below,
the groove is comparatively deep at the upper end, and
gradually diminishes in depth as it descends, until, at the
periphery, it totally disappears, leaving the grinding faces
smooth and even, thus effectually preventing the escape of
the ore until it is reduced to the finest powder.
III. CONCENTRATION.
SEC. 34.
Division.
Concentration by means of water, depending principally
on the difference of specific gravity, will be treated here in
two parts.
The first will consider the concentration of
coarse stuff from the size of a walnut to one-thirty-second
part of an inch diameter-" concentration by relative resist-
ance to a free fall in standing or moving water." The second
part treats of the concentration of fine stuff from one-six-
teenth of an inch to the finest slime-" concentration by resist-
ance on an inclined plane." There is great difference in the
arrangements and methods of these two divisions, both of
which, however, are often found operating in one and the
same establishment. Jigging separates the coarse ore parti-
cles from similarly coarse gangue, which latter, still involving
ore in a finer condition, must either be further reduced for a
second jigging, or directly transferred to fine crushing after
the first jigging, and concentrated on percussion or other
tables.
Although it is quite evident that this method is the most
rational, that is, to save the coarser ore particles by jigging
before the whole mass of ore is crushed fine, whereby a greater
loss must ensue, still it cannot be denied that circumstances,
as they are in California, Nevada, etc., do not permit adopting
the combined method of jigging and concentration of fine stuff
from the same ore advantageously. But there are cases where
130
CONCENTRATION.
I
jigging or the rotating cylinder, (§ 40) may be introduced very
profitably without fine crushing. This refers especially to
lead and copper ores. A coarse reduction by rock-breakers,
and application of proper machines for concentration of coarse
material, admits of putting through great masses of ore with
a comparatively small investment. The loss involved in not
crushing the residue of this operation fine must be submitted
to, otherwise in many cases no profit could be realized.
SEC. 35.
Concentration of Ore Grains, (Jigging Stuff).
The principle on which the concentration of coarse stuff or
grains is based, the principle of the free influence of specific
gravity in a column of water, whereby separation of the ore par-
ticles takes place while falling, is the true principle in concen-
tration. The jiggers, dolly tub, the Setz-rad, (rotating wheel)
and the rotating cylinder, apply the above principle. With
the jiggers the application is defective, inasmuch as the free
fall of grains is too short, but a successive lifting of thirty to
forty times, or more, allows the denser ore to separate from the
gangue very perfectly, equalizing irregularities of continuous
feeding as well as the unfavorable influence of the varied
shape of particles, which will occur in the best separation.
In this respect it seems that well-constructed self-discharging
jiggers gain over the rotating cylinder where the grains are
exposed to only one free fall; but on the other hand, the
time of the fall depends on the height of the cylinder, its di-
ameter and speed, by which the falling time can be prolonged.
The falling speed of grains is very important.
Rittinger found that :
a. A round globule of galena, one-eighth of an inch in diam-
eter, and a quartz globule of four-eighths of an inch diameter,
will both reach the bottom of a column of water at the same
CONCENTRATION.
131
time. The volume of the quartz globule is sixty-four times
that of the galena, and the absolute weight twenty-two times
as great as that of the galena globule, which arrives at the bot-
tom at the same time.
b. Crushed ore particles differ in shape, representing three
main classes of the following proportion:
1. Roundish grains about.
2. Oblong
(
3. Flat-shaped
((
((
{
*
..50 per cent.
.25
25
The falling speed in water of the round grain is=112; of
the oblong=97; and of the flat-shaped particles-79.
The proportion of these three classes varies according to
the internal structure of the mineral. Galena, breaking into
cubes, will produce nearly sixty per cent. Quartz, breaking
irregularly, only forty per cent. of roundish grains. Calc-
spar agrees pretty nearly with the above proportions.
SEC. 36.
Jigging.
The smalls obtained from breaking rock in the mine, from
cobbing and spalling operations, from rolling and coarse stamp-
ing, after being sized by proper sizing apparatus, are intro-
duced on a sieve and subjected to an upward thrust of
water, by which the whole mass is lifted up. When this
action of the water ceases, the grains fall down under influ-
ence of specific gravity. The heavier particles will reach the
bottom first, then the lighter stuff. But the free fall, being
so short, is greatly obstructed by the mass of the grains them-
selves; and it is, therefore, necessary to continue the jolt or
upward thrust of water in quick succession. The denser part
will finally be found on the bottom of the seive, so that by
removing the upper layer of gangue the separation is effected.
To the jigging operation, all such stuff is subjected as is too
small to be picked, too poor to be directly smelted or amal-
132
CONCENTRATION.
gamated, and too rich to be reduced by crushing for concen-
tration on tables, where a considerable loss cannot be avoided,
while by means of jigging the richest or heaviest part is sep-
arated and saved from being pulverized to a floating condition,
which would involve a loss on the best concentrating contriv
ance.
The conditions upon which the full benefit of jigging can
be obtained are the following:
1. The ore or smalls must be separated according to size
as much as possible, and treated separately. The less the
variety of minerals, the greater the difference of specific
gravity; the cleaner the ore particles are, so much the more
perfect will be the concentration.
2. The upward thrust of the water, or the sudden fall of
the sieve, must be perpendicular and short, and not in too
quick succession, so that the particles find time to reach the
bottom before another lift is applied.
3. The stuff should be neither too coarse nor too fine. In
the first case, the absolute weight increases, and the larger
pieces are generally mixed masses of different ores, so that
the separation cannot be well effected. If too fine, then the
action of specific gravity decreases, and the water cannot
penetrate among the fine particles quick enough.
4. The size of the meshes of the sieve must correspond
with that of the grains; and
5. Smalls consisting of ore finely disseminated in the
gangue must be excluded from jigging.
Ores composed of minerals of different specific gravity-
for instance: quartz, heavy spar, galena, copper and iron
pyrites, carbonates, etc.-require to be reduced fine and
properly sized. Although, as before mentioned, coarse ore
particles are extracted by jigging, being thus saved from
wastage in concentration, local circumstances, as those of
California and Nevada, for instance, must be considered in
determining whether it is more advantageous to crush the
ore at once suitable for concentration on table, instead of
having jiggers which never finish up the work, but always
CONCENTRATION.
133
yield a portion to be crushed over and concentrated; or
whether it would pay better to use jiggers, and to consider
the poorer stuff as refuse. This last consideration may be
important in regard to the poor waste rock of copper and
lead mines, where water is scarce, and the value of those
minerals comparatively low. Silver ores in Nevada are
treated more economically by direct concentration.
The jigger is a round, square or oblong sieve, two feet in
diameter, or two by two, or two by four feet, the wooden
sides from four to nine inches deep. The jiggers are gen-
erally suspended on a rod connected with a lever, by which
the required motion is given, often by hand. The sieve
plays in a kieve or hutch, filled with water. The motion is
often imparted by short cams from a revolving shaft. This
motion is regular, but the jolt is not quite so effective as that
produced by hand.
In place of the movable sieves, stationary ones have been
successfully introduced. The lifting motion is then given to
the water by means of a piston. In all instances, however,
the refuse, as well as the concentrated part, has to be
removed by hand at intervals. The new construction of
self-discharging jiggers is, therefore, a great improvement.
Although the working of the continual jiggers is not yet
perfect, still great quantities of smalls can be separated so
far that only a small proportion, if any, of the whole bulk
has to be re-jigged by hand.
The machines in use are movable jiggers, stationary jig-
gers, with a piston below or on the side, and continual jiggers.
SEC. 37.
Movable Jiggers.
Fig. 1, Tab. IV, shows a round movable jigger, as used in
Freiberg. a, represents the platform for the stuff, having an
open side towards the jigger. The sieve, b, is suspended on
134
CONCENTRATION.
the iron rod, l, connected with the balance, c, five feet eight
inches long, resting on the journal, d. On one end of c, is a
box, e, with about one hundred pounds of rock in it for a
counter-weight. f, is another rod, with a handle, g, sliding
in h. The sieve, b, eighteen inches in diameter and seven
inches deep, is suspended within the tub, moving in the
guides, r, r. The tub is two feet nine inches deep-thirty-
eight inches in diameter above, and twenty-eight inches at
the bottom.
There are three jiggers, the sieves made of iron wire.
No. 1 has four meshes to the square inch; No. 2, sixteen,
and No. 3, twenty-five. Four iron rods are fixe below the
sieve to support it. The operation is the following:
The unsorted smalls are introduced, by means of a shovel,
into the sieve, No. 1, filling it about half full. Spreading
them even, the workman sinks the jigger below the water
surface, and gives, by means of the rod, f, from thirty to
forty short intense jolts. All the stuff which is finer than
the holes falls through into the tub, while the remainder sep-
arates, so that the heaviest lies on the bottom. The sieve is
then lifted above the water, and the upper poor stuff scraped
off with an iron scraper ; but the ore particles in a stratum
of one-half to three-fourths of an inch remain undisturbed.
The sieve is charged again and jigged repeatedly as before,
and so on, until the metalliferous part covers the bottom
about three inches high, whereupon it is taken out, and the
same operation repeated, until the material falling through
the sieve accumulates on the bottom of the tub to a depth of
about twenty inches.
This material is then discharged into a sluice with an
ascending bottom, and stirred in a constant stream of clear
water, for the purpose cf getting rid of mud and slime. It
is then ready for the jigger No. 2, which is charged and
treated in the same manner, applying somewhat shorter and
more gentle jolts. With this stuff also other material of the
same character from stamping is treated at the same time.
After forty or fifty jerks, a thin layer of refuse, and another
CONCENTRATION.
135
of one or two and a half inches in thickness are drawn out.
The latter is suitable for crushing. The remainder is stirred
up a little, the jigger filled, and jigged again as before.
This ore (in Freiberg) contains, besides galena, also silver
ore and zinc blende. Hence, after four or five charges
between the lowest deposit of galena and the middle stuff or
upper layer, a layer of silver ore and zinc blende three-
fourths of an inch to one inch thick is taken off separately.
The galena, when it accumulates in sufficient quantity, is
subjected once more to jigging, in order to separate the
silver ore, of which some still remains with the lead ore.
On account of more uniform size of the grains, the sieve No.
2, although that which falls through the sieve is always
richer, yields refuse rock, while none is obtained with No. 1,
from which all the scraped material is a middle ore for crush-
ing and further concentration. From No. 1 jigger is obtained
middle ore, concentrated ore, and finer sediment. From No.
2, refuse rock, middle ore, concentrated silver ore, coucen-
trated galena, and sediment.
The sediment from the second jigging operation is washed
in like manner as that from No. 1, and subjected to jigging
on the sieve No. 3. The procedure does not differ from
that of No. 2. The educts are crushing ore, silver ore,
galena and sediment. The last is delivered to the smelting
furnace after being dried and pulverized.
The jigging of smalls without preceding regular sizing is
practiced only where want of sufficient water renders it
necessary. A properly sized stuff gives a better and quicker
result. On the Harz, the sieve is forty inches diameter and
one foot deep, having a speed of eighty jerks per minute.
According to the size of the sieve and quality of ore, a work-
man can put through from four to six tons in ten hours.
136
CONCENTRATION.
SEC. 38.
Stationary Jiggers.
A. Hydraulic Jiggers, with a piston on the side. These
jiggers are very suitable for coarser stuff. The piston serves
either for one or for two jiggers. A double jigger consists
of a rectangular box, six feet by two, divided into three
equal compartments. The middle box receives the piston.
The two outside boxes have stationary sieves, (perforated
plates, or iron or brass wire sieves) each two feet square.
The compartments communicate with the piston room by
openings a few inches below the sieves, which can be closed
alternately with slides by means of levers.
The tanks are filled with water sufficient to cover the ore
on the sieve. The piston has a lift of four to five inches and
forty-five to fifty strokes per minute. The downward motion
must be rapid, so that the whole mass of smalls may be lifted.
The upward motion, however, must be slow, so as not to soak
below the sieve, which, if worked by mechanical power, is
regulated by a counter-weight, having the piston rod inde-
pendent of the driving arrangement. The agitation is con-
tinued for five or ten minutes, according to the richness of
the ore.
It is of importance that the effect of the water be
uniform on the whole surface of the sieve.
The grain sizes subjected to jigging are from one-sixteenth
to one-eighth of an inch; in other places, from one-sixteenth
to three-fourths of an inch.
The double jigger is attended by one man, who regulates
the opening of the gates, shutting them alternatively, so that
one stroke is applied to one sieve, and the next to the other.
The machine requires about a quarter of a horse power, and
67.5 cubic feet of water, (=363.3 gallons per day.) About
two tons of ore can be jigged on one hydraulic sieve in ten
hours; the quantity, however, depends very much on the
quality of the material. The uniform lifting of the smalls
CONCENTRATION.
137
depends much on the height and position of the opening,
which is best determined by experiments. In the Harz it is
from five to seven inches high.
Petherick's Separator.-This jigger comprises four round.
sieves with sides, grouped round a piston in the centre of a
square box, so that each sieve occupies one corner of the
box. The piston moves in a short cylinder, and causes the
water to rise and fall alternately in the sieves. The variation
in extent and quickness of the motion required for different
ores is easily produced by a simple arrangement. This jigger
is used in Cornwall, giving much better results than the com-
mon jigger.
B.
Stationary Jigger, with the piston below the sieve.
This arrangement differs from the hydraulic, by having the
piston in a box below the sieve. The rod of the piston passes
either through the fixed sieve or the rod divides into two
arms, which pass on the sides of the sieve. In this machine
the upward motion must be quick, in order to lift the smalls.
To facilitate this, since there is a tendency to create a vacuum
below the piston, canals from the side convey air into the
box. This makes the machine more complicated, and its
treatment requires more attention than that of the preceding
jigger. The movable jigger, the Stationary Jigger with the
piston on the side, and the Stationary Jigger with the piston
below the sieve, do not vary much in efficiency, provided all
are properly constructed and managed.
One square foot of sieve area can ordinarily work but four
cubic feet of stuff per hour; but in case the stuff is poor, two
or four times as much may be put through. The stationary
jiggers require more power, from 1-10 to 1-20 horse power to
the square foot of sieve, making from fifty to eighty strokes
per minute.
Upon all three kinds of jiggers grains from 0.078 to 0.64
of an inch can be sorted with equally good results.
Finer stuff than 0.078 is difficult to treat, as the water can
10
138
CONCENTRATION.
not penetrate regularly the compact layer of stuff, but lifts it
as a whole with local breaks. Of such material only small
quantities at a time can be treated with success.
On the other hand, coarse stuff above 0.64, and up to 1.26
inches, can be separated advantageously, but the refuse or
upper layer must be subjected to picking, while that below
0.64 is subjected to mechanical reduction.
All these jiggers require, under similar circumstances, an
equal number of strokes, but the hand jigger is attended by
one man, who scrapes off the refuse as soon as the separation
is effected, while two machine jiggers are attended by one
man, who requires more time for the scraping than needed
for the jigging, consequently the jigging of one machine con-
tinues longer than is necessary, while the man is busy with
the other. This is the reason why a hand jigger yields some-
what more than the machine jigger.
Whether the refuse or scrapings are thrown away, or
subjected to further operations, depends on local circum-
stances. In many cases the uppermost layer may be con-
sidered worthless. The middle scrapings are retained
separately, and either jigged over a second time directly,
or reduced smaller, and then jigged or crushed and con-
centrated.
SEC. 39.
Continual Jiggers.
The Pacific States are foremost amongst the mining coun-
tries, whose working system requires the substitution of
machinery for hand-work as much as possible. For this
reason continual jiggers, as well as other self-acting concen-
trating and self-discharging machines, are here of more im-
portance than machines depending on the skill and attention
of the workman.
Continual jiggers have been in practical use for nearly
fifteen years. Well regulated self-discharging machines of
CONCENTRATION.
139
proper size can separate about two tons of stuff per hour, of
lead ores, in 3-16 of an inch grains.
There are many differently constructed contrivances of
this kind, some of which are described in the following:
A. Percussion Jigger, (Setz-herd).—This jigger, invented
by Rittinger, and for many years in successful operation, is
represented on Tab. VI, Figs. 1, 2, 3. There are six upright
posts, lined with planks, a, b, c, and d, Fig. 2 forming the box
for the pump and sieve. This space is divided by a partition,
e, Fig. 1; the larger compartment serves for the piston, d',
and the sucking valves, f; the smaller, g, which communicates
with the former below the partition, e, receives the water,
which is lifted by the piston. This compartment widens on
the top, to receive water dropping from the sieve above.
The piston space is lined with oak boards, h, h, which are
easily changed when worn. The sucking valves are stationary
in the piston box. There is the valve-frame, i, fitted below
the oak lining, and supported by the lists, i'. The valve-
frame is divided by cross-lists, k, into six openings. The six
valves, ff, are of leather, strengthened on the upper side by
iron plates one tenth of an inch thick. The frame consists
of two pieces, and can be taken out through the apperture,j.
The opening,j, and the one above the valves, 1, Fig. 2, serve
for the purpose of clearing the box and valves of the fine
stuff which passes the sieve. The cover, m, of these openings,
is furnished with leather strips, in order to make the box
water-tight.
The box is provided with water by the pipe, n', and can
be emptied partly by opening the plug-hole, o. The water,
which would accumulate with the sorted sands in the com-
partments A and B, flows on the concave bottom into the
launder, p.
The jigg-piston consists of a frame, d', thirty-five and a half
inches by seventeen, and four and a half inches high, divided
by cross lists into four partitions. The lists are sharpened.
downwards, so as to facilitate the downward motion of the
140
CONCENTRATION.
piston. On the lists rest four valves, r, r, opening upwards,
and constructed like those below the piston. The packing
of the piston consists of leather strips surrounding the frame,
one and a half inches wide. This piston is moved by
the crank rod, s, which is fixed to the cross-piece, u; the
piston rods, t, are also screwed to the same cross-piece. To
secure a firm connection of the frame and piston-rod, t, Fig.
2, the latter spreads into two horizontal flat arms, which are
bolted to the long sides of the frame. The rod, t, moves in
a half-round vertical hole of the box side. In order to form
a better guide for the piston rod, as well as for the jigg-frame,
o', there is a lining, n, Figs. 2 and 3, on the sides, b, of the
box. This lining is seven inches and a half wide, seven feet
long, and extends from the back wall, w, to the front posts.
The frame, o', with the sieve, 4, is suspended in the
upper part of the box. The front part of the frame, y',
which strikes against the percussion block, y, is made of oak
three inches thick.
The sorting sieves, 2 and 3, above the canal, d, are the
most important part of the whole apparatus. The sieve, 4,
with a step above the canal, is made of sheet-iron with square
or round holes, is from one and a half to one-eighth of an
inch thick, and is nailed to the frame from below. The step
serves the purpose of widening the passage between the
sorting sieves; 8, 8, are iron bands to strengthen the frame.
The arrangement of the sorting sieves 2 and 3 is shown in
Figs. 1 and 3. Two hoops, 7, 7, are screwed on both sides
to the frame, the upper part of which can be taken off by
unscrewing it, as shown in a larger scale, Fig. 4, Tab. VI.
By these means, the sieves, 2 and 3, are easily removed.
The hoops widen in the middle, and are provided with two
screw-holes for the reception of the set screws, 5 and 6,
furnished with nuts, by which their vertical position can be
changed. The upper set-screws, 5′ and 6', are provided with
slits, into which the sieves are placed. As far as the sorting-
sieves reach, the inside of the frame is lined with sheet-iron,
It is of importance that all the parts of the sorting
v.
CONCENTRATION.
141
arrangement should be united in a solid combination, to with-
stand the concussion.
The sorted sands are discharged into the compartments,
A, B and C. In order to prevent the passage of the pumped
water through the space between the frame and lining, î,
there is below the sieve a packing of leather two and a half
inches wide; and to prevent sand from falling accidentally
between the lining and frame from above, there are sheet-
iron strips, m', m', Fig. 3, screwed to the lining, n, covering
the slit between them.
The frame is suspended on the four rods, v', v', regulated
by set screws. In front of the sieve-frame is the percussion
block, y, fastened to two posts on each side by long bolts,
Fig. 3, which may be raised or lowered in oblong hubs in
the posts.
The feeder, c', hangs on an iron fork. At the bottom is a
tongue, e', which strikes against a screw, in order to promote
the discharge. By bringing the head of the screw nearer or
further from the tongue the blow will be weaker or stronger.
The slide door, d', regulates the opening. The cam, z',
moves the feed-box, and also, by means of the lever, z, and
the wooden spring, x, the jigger.
There are different motions with this jigger; a horizontal
one of the sieve, and a vertical one of the water, from the
action of the piston.
These two motions can not take place at the same time.
The principal separation is effected while the water, raised
by the piston, lifts the different grains according to their
relative specific gravity. This action must not be disturbed
by the horizontal motion, much less by the percussion which
takes place on the sieve frame at the discharge side. Both
motion and percussion must take place during the downward
motion of the piston, in such a way as to obtain a slow
swinging motion, and a quick percussion, shortly before the
piston reaches its lowest point. The swing of the frame
should not be more than from two to four inches.
The vertical motion effects the separation; the horizontal,
142
CONCENTRATION.
the discharge. The feeding takes place continually at one
end of the jigger, by means of a hopper. As the stuff moves
forward, and the separation progresses, it reaches the dividing
sieves as represented in Fig. 14, Tab. IV, (the latest approved
position). The heaviest portion of smalls on the sieve, a, is
separated from the upper less valuable layer by the sieve, b,
and this from the uppermost refuse by the sieve, c. The
position of the three sieves, and their relative connection are
very important and exact, as found by long experience. A
small change would interfere with the regular discharge and
concentration.
The percussion spring must not be strained too much. It
is sufficient if the sieve receives a single shock, firm, and
without vibration, and plays between fifty and sixty times
per minute. The piston, having the same speed, has a lift
of from two to three inches, which is sufficient for grains
between one and four-eighths of an inch. The jigger works
best if about three or four inches depth of stuff is kept always
on the sieve.
Water is introduced by the pipe, n', and the shaft put
in motion. The water must cover the smalls, and remain
nearly at the same level during the play of the pump. The
water is allowed to run constantly into the box, but only
sufficient to replace what is carried out with the smalls. The
gate, d', of the self-feeder is regulated so that the discharge
is equal to the charge, keeping always a layer of about three
inches depth of smalls on the sieve. The separation of the
stuff commences immediately, the charge progressing towards
the dividing sieves, Fig. 14, Tab. IV. Richer ore will of
course deposit a thicker stratum of concentrated stuff on the
bottom of the sieve, and the dividing sieves must be arranged
accordingly. The distance of the sieves ought not to be less
than half an inch; or, if coarser stuff is treated, not over one
inch.
The quantity of stuff which can be put through in a given
time depends on the width of the sieve, on the number of
strokes, and on the proper condition of the pump. A sieve
CONCENTRATION.
143
of fifteen inches width, containing three and a half square.
feet of jigging surface, and with fifty to sixty strokes per
minute, can separate from thirty to forty cubic feet of stuff
per hour. One man attends two of these percussion jiggers,
of which each requires three-quarters of a horse-power, and
has a piston three feet by eighteen inches.
B. The Continual Cylindrical Jigger is one of the self-
discharging jiggers used for many years in the Harz mines.
Tab. VI, Fig. 8, shows a cross section. There is a large
kieve, a, nearly cylindrical, inside of which is a conical
bottom, c, ending in a tube, b. All the material which falls
into this part of the kieve is carried out through this tube into
a box, x.
Within the cone, c, is another funnel, d, of cast-iron, ending
in a spout, h. The funnel is attached to a cylindrical ring, e,
resting on wooden supports, f, f, one inch in thickness.
Inside of the cone there is an iron cross, i, on which the
tube, m, is fixed. This tube goes through both cones, leading
the stuff into the box, z.
The circular sieve, n, is made either of iron or brass wire,
with meshes of about one-sixteenth of an inch. The diameter
of the sieve is twenty-six inches. It is fastened to a wooden
circular hoop, o, o, which reaches three and a quarter inches
above the sieve, and is fixed to two arms, q, q, by which it is
connected with the lifting rod, t. To this rod vertical jerks
are imparted by cams. The edge of the sieve is beveled all
round, so that the lifted lighter particles of the smalls may
more easily fall over the edge and be carried out through the
spout, b. The beveled edge is overlaid with sheet iron,
covering the rim of the cast iron ring, e.
In the centre of the sieve is a zinc plate with a hole three-
quarters of an inch in diameter. This plate is fixed to an
iron or zinc pipe, in which the tube, m, fits. Above the
opening of the plate, s, is a solid cone, u, the base of which
is four and a half inches in diameter, and only three-sixteenths.
of an inch distant from the sieve. Through this cone there
144
CONCENTRATION.
is a screw with a tapered end, which, if screwed down, closes
the hole, s, leading into the tube, m.
The stuff is conveyed to the centre by a trough, w. When
in motion the apparatus is filled with water, and the central
opening, s, closed by the screw. The lighter particles are
carried over the rim of o into the box, x; and, if it is the
refuse of rich ore, either crushed finer or rejigged, or it is
considered waste if the result of poor ore. The heavier
particles accumulate at the bottom. After some time the
rod of the cone is screwed up, and the richer stuff gradually
carried out into the box, z. The finer part which falls through
the sieve passes into the compartment, y.
These jiggers are also made square or oblong, and so
arranged that the light stuff, passing over the rim of the first
sieve, enters another one of the same construction. The
oblong sieve is fed on one of the narrow sides, and discharges
on the opposite. The sieves are not quite level, the centre
being somewhat deeper. In Clausthal the meshes are one-
sixteenth of an inch wide.
Between one hundred and eighty and two hundred jolts
per minute are given to the sieve, and the lift is only one-
eighth of an inch, so that it looks more like a vibration.
About two hundred and fifty-eight cubic feet of fine stuff can
be jigged on this machine in twelve hours.
Other self-acting jiggers are so constructed that the sieve
is stationery. The lifting of the stuff is effected by means of
pistons. One of this sort is the
Continual Jigger, with the piston on the side. Fig. 5, Tab.
VI, shows a central vertical section of this machine. It is a
square oblong box of two compartments, a and b. The latter
contains the piston, c, provided with leather packing. The
piston rod, d, is so constructed that it comes out of itself
when ascending, followed by the swimming piston. By this
means the soaking is prevented.
The compartment, a, contains the sieve, e, with very fine
meshes, about one-fiftieth of an inch holes. There is an open-
CONCENTRATION.
145
ing in the centre, i, through which and the trough, f, the
concentrated ore is discharged. There is an iron rod, g,
playing in the box, h, moved by the lever, k, by means of
the piston rod, d. This rod passes through a cone, m, and is
provided at the end with a nut, by which the opening, i, can
be closed. With the downward motion of the piston, the
rod, g, is lifted, and with it the shutter, so that the concen-
trated grains enter the opening, i, while at the same time the
refuse is thrown out at n. This conduit is on one side of the
box, four inches above the sieve.
The fine stuff which falls through the sieve on the bottom.
o, is removed, from time to time, through the gate, p.
The fine-grained stuff is charged continually on the sieve,
and is lifted from sixty to sixty-five times per minute by a
stroke of from one and one-fourth to one and seven-eighths
inches. Both compartments are filled with water. The
concentrated part discharged through i, is generally sub-
jected to a second concentration on a similar apparatus,
thereby producing stuff suitable for smelting. The re-con-
centration is necessary in treating as fine a grain as is
adapted to a sieve of the described fineness. The thick
stratum, compared with the fineness of the grains and the
height of the lift, are circumstances increasing the difficulty
of concentration.
The construction of this machine shows that the shutter,
g, opens at the downward motion of the piston, and shuts at
the upward motion. Coarser grains, however, would proba-
bly require the discharge, i, continually open, as described
with the jigger ($39, B).
The advantage of the continual jigger is so great that the
old contrivances separating by charges are rapidly going out
of use. They are retained, in some instances, to re-concen-
trate the educts of continual jiggers.
Another Hydraulic Jigger, continually self-acting, is repre-
sented by Fig. 7, Tab. VI. The front part, b, over which the
gangue is carried and discharged over a partition, d, is mov-
146
CONCENTRATION.
able at c. By this means the slit, i, between b and the sieve,
a, can be made wider or narrower. Through this slit the
denser stuff falls into the compartment, e. The sieve, a,
which is stationary, has an inclination towards the discharge
of from five to eight degrees.
The ore is charged through the hopper, f, and water suffi-
cient to replace the waste is conducted through the launder,
h, into the compartment, g, which communicates with the
compartment, k.
During the downward motion of the piston, the water
passes in two directions-first, through the sieve over b, and
and then through the openings, w, into the compartment, g.
These openings are sometimes provided with valves, by
which the water is prevented from flowing back into g.
While the piston is playing, the stuff moves gradually
forward towards i, and falls into e. It is necessary that the
sieve should project over the partition, m.
The opening, i, must be regulated by degrees, until both
discharges, through i, and over b, appear to be of the right
quality. The accumulated concentrated part of e, is either
discharged at intervals, by taking out a plug in 7, or the
spout is made smaller, so that the stuff comes out continually
with some water. Where water is scarce, it may be returned
to g, by an elevating wheel.
The piston is moved directly by a simple crank, so arranged
that the stroke may be changed.
SEC. 40.
Rotary Machines.
A. Rotating Cylinder (Strom-setz Maschine).—This concen-
trator, invented by Hundt, may be ranked with jiggers, as it
follows the same principle, although there is in this machine
no jigging of grains whatever, as is the case with all the
preceding contrivances described in this chapter.
CONCENTRATION.
147
To illustrate the action of this concentrator, we may imag-
ine a column of standing water, into which a portion of ore,
the particles of which are of uniform size and shape, but of
different gravity, is introduced.* The heaviest particles
will reach the bottom first; then in succession the lighter
ones. If the charges should follow at intervals, and the
quickest falling grains be removed from the bottom after
each charge, the separation would be completely effected.
To the practical execution of this idea, however, there are
so many obstacles that no machine for this purpose has ever
succeeded. But there is another way in which the same
result can be obtained in a very simple manner. Instead of
removing the heavy grains from the bottom of the standing
water, which could be effected only at intervals, (as is done
with the dolly-tub under different circumstances) Hundt
gives to the water a circular motion by a revolving cylinder
above a stationary bottom, and the problem is solved. The
grains have now to follow two different motions; one, depend-
ing on the gravity of the particles, is vertical, the other
following the rotating water, is horizontal. The grains,
therefore, must take a diagonal course, and while the densest
particles reach the stationary bottom first, the lighter, slower
falling grains are forced by the horizontal motion of the
water to reach the bottom behind the heavier ore, whereby
a separation is continually effected into several classes.
The favorable result of this concentrator, compared with
jiggers, and its simple construction, is likely to replace not
only many jiggers, but perhaps also the hand buddle, per-
cussion tables, and other similar arrangements employed for
the concentration of coarse and middle-grained stuff. Figs.
2 and 3, Tab. IV, represent Hundt's concentrator. 2, is a
vertical section; 3, the top view. a, is a circular vessel,
twenty-three inches deep and nearly five feet in diameter.
*Charging the rotating cylinder with unsorted stuff, the separation would go on
according to equal-falling grains, (§35, a) of which the densest are the smallest.
The compartments would then contain assorted grains of larger sized rock and
smaller ore particles, so that a simple sifting would separate the ore from gangue.
148
CONCENTRATION.
In the centre is a cone, a', on the top of which runs the per-
pendicular shaft, h. The tub, a. is divided into twelve radial
compartments, b, c, d... g, which are equal or variable in
size. The partitions, b', c', are seventeen inches high. Each
compartment has a discharge-pipe, i. There is an iron (or
wooden) cylinder, k, which fits tightly into the tub, a, pre-
venting the escape of water.
On the shaft, h, is a double cylinder of boiler iron attached
by means of arms, and l'. The outer cylinder, m, is four
feet in diameter. The inner, n, has a conical shape, with the
larger base below, leaving a space of two inches all round
between m and n. The double cylinder rotates in water, and
it is necessary to have the water between. Both must rotate
with a regular and uniform velocity. For this reason there.
is in the upper half of the space a sheet-iron partition, o, and
opposite, in the lower half, another one of the same kind, p.
By means of these perpendicular partitions, the water
assumes a steady regular motion.
The ore is introduced between the revolving double cylin-
der at q, which is stationary. The apparatus is put in
motion after being filled with water by r, up to the rim of
the conical cylinders. The outlets, i, if water is scarce, are
closed, and the ore admitted between the cylinders at t, over
a dividing sieve, which is not in the drawing. If the motion
of the water takes the direction as indicated by the arrow,
the heaviest part will fall or sink to the bottom about in the
direction of the dotted line, 1, the next in 2, the still lighter
in 3, and so on through the two-inch space, u, into the com-
partments, b, c, d. It is obvious that when the feeding is
continuous, as well as the motion of the water, the separation
of the homogeneous matter will also be continuous into the
respective compartments. When the compartments are
nearly full, the separated stuff is discharged at i, which is
quickly closed again, so as not to let out more water than is
necessary for the discharge of ore.
Where water is abundant, the openings, i, are regulated
for continual discharge. In this case, sufficient water must
CONCENTRATION.
149
be conveyed by r, constantly, to keep the water surface
always level with the inner cylinder edge.
One rotating apparatus requires hardly one-twentieth of
one horse-power. The motion is either transmitted to the
pulley, n', or the cylinder, m, is made higher, as indicated by
the dotted line, v, and the belt or rope applied directly to it.
The size of the grains suitable for this apparatus ranges
between one-sixtieth and three-fourths of an inch and above.
Coal can be separated from pyrites and rock in much larger
pieces; but the dimensions of the machine must be altered
accordingly.
After a long practical operation at Siegen, the following
conclusions were drawn: In treating grains over three-
eighths of an inch, the apparatus, with a five-foot water
column, requires three revolutions per minute. Below that
size, two revolutions and three feet water column. Coal
requires two revolutions and one and one-half feet of water.
When the column of water and speed for a certain size of
ore are decided upon, any workman can attend two of these
concentrators, even in case of double charges. Whatever
size of grains is used, always the diameter of the single fed
apparatus, height of the water, and the speed, must be in
such proportion that all particles which are charged at a cer-
tain point will reach the bottom before one revolution of the
water is completed. A revolving cylinder of five feet diam-
eter has a circumference of 15.7 feet. The coarser the stuff,
the sooner all the particles must reach the bottom. Grains
over one-fourth of an inch in diameter will settle on a peri-
phery of six feet length, so that an apparatus of four feet
in diameter can be fed in two places at the same time (at
x and y, Fig. 3), giving to the cylinder three revolutions
per minute. In this case, one ton of ore per hour can be
separated.
Grains over three-eighths of an inch, with single feeding,
require five feet water height and two and a half feet diam-
eter of the rotating cylinder. Grains below three-eighths of
of an inch separate satisfactorily with four feet of water and
150
CONCENTRATION.
four feet diameter of cylinder. Apparatus with two, three,
or four feedings, must be two, three or four times as large.
An apparatus of four feet diameter answers for all sizes;
but the height and speed of the water must vary with each
size. A speed below one or above six revolutions rarely
occurs.
Where there is sufficient water to spare, it can be arranged
so that the continuous flowing off shall take place in the
centre, x', of the tub, a, giving to the bottom a shape as indi-
cated by the dotted line, x". The advantage of this arrange-
ment would be in cases where muddy or slimy stuff was to
be separated. All mud and very fine particles would be car-
ried over the inner cylinder, w, out of the apparatus.
With a careful discharge of the separated stuff at i, very
little water is lost. On account of this, and the small amount
of power required, the independence of skillful workmen,
the ease of regulation, and the amount of stuff which can be
put through in twenty-four hours, (twenty-four tons of a cer-
tain size) this apparatus seems to be eminently suited for the
silver, copper, and especially the lead mines of Sonora, Ari-
zona, etc., where water is scarce and ores for concentration
are abundant.
B. Rotating Wheel (German, Setz-rad).—This concen-
trator, invented by Rittinger, (first tried in 1863) is founded
on the same principle as Hundt's, (§40, A) which is said to be a
later invention, differing only somewhat in construction.
Instead of having the cylinder revolve, by which a circular
motion is given to the water column, the cylindrical tub of
the "Setz-rad" is stationary, and the motion is imparted to
the water by a vertical wing-wheel, the shaft of which is in
the centre of the tub, (forty-two inches diameter). The shaft
is provided with a drum, (sixteen inches diameter) to which
eight wings of sheet-iron are attached, surrounded and con-
nected by a cylinder of sheet-iron.
At the bottom of the tub are eight radial partitions, ending
in small funnel-like holes, each of the eight connected with
a discharge-pipe outside of the tub, leading upwards as high
CONCENTRATION.
151
as the pressure of the water can force the sands through.
The pipes empty into smaller tubs placed around the main
tub. These receiving-tubs stand on a circular launder, by
which the water flowing over from the tubs is conveyed to
an elevator close by, and by this means returned to the appa-
ratus.
The feeding, as in Hundt's concentrator, is continual, and
is effected by means of a hopper, or directly from the sifting.
The sand separates, according to density, during the trans-
verse descent, and settles in the different compartments
below the wings, from which it is conveyed through the dis-
charge pipes into the receiving tubs.
The height of the wings, the diameter of the wing-wheel,
and the number of revolutions, are the points upon which
the performance of the machine depends, so that after the
right proportion of the first two is established, the separa-
tion of different grain classes depends on the change of speed
alone. The more carefully the classification of the ore is
performed, the closer will be the separation of the metallifer-
ous part; and as coarse sand is easier classified than finer,
the separation of coarser stuff will always be more perfect,
so that, for instance, with grains of five-thirty-seconds of an
inch, (diameter) ninety-one per cent.* of all the lead con-
tained in the stuff will be found in one single compartment,
(in the second of the eight) and eight per cent. in the next,
(the third) while in treating grains of two-thirty-seconds of
an inch diameter, there is found only seventy-five per cent.
in the second, and twenty per cent. in the third compart-
ment.
The number of revolutions must be regulated according to
the size of the grains, the specific gravity of the ore and
gangue to be separated, and also according to the proposed
degree of concentration, and must be found by experiment
for each particular case.
C. The Dolly Tub, or Packing Keeve.-This apparatus is
*Rittinger's Erfahrungen, 1865.
152
CONCENTRATION.
employed in some lead mines in England; but, considering
the time required for separation of one charge, the hand
labor is costly, even if the "machine dolly tub " is employed.
The charge and separation take only half the time of the
whole operation. The dolly tub acts on the same principle
as the two preceding continuous machines, but offers the
advantage of being exceedingly simple. This machine can
be used also as a slime and sand separator, or sizer.
The dolly tub consists of a kieve, with a dolly or stirrer,
like those of agitators, but movable, and arranged with
hasps, which can be loosened quickly; or the dolly is con-
nected with a lever, if worked by machinery. The operation
is the following: The tub is about two-thirds filled with
water, the dolly introduced, and by turning it rapidly, the
water is caused to assume a circular motion. The tossing is
then commenced by shoveling in the stuff, until the water is
rendered somewhat thick. The stirring is continued for a
short time, the hasps loosened, and the dolly suddenly with-
drawn. The tub is then packed by striking its outside with
a heavy wooden mallet. After this operation, the water is
drawn off through plug-holes in the side of the tub.
If the stuff to be treated by the dolly tub is unsized, the
heavier and larger grains settle first; but the result is more
sizing than anything else. The free slime forms the upper-
most stratum-the tough is carried out with the water.
With sized sand, the concentration is effected very well. In
the centre of the bottom is a small conical nucleus, contain-
ing ore and coarser sand. The next stratum is the richest.
Dollying seventeen hundred pounds of Sandschlich lead
ore, much intermixed with carbonate of iron, and containing
forty-eight per cent. of lead, gave the following result after
forty-two minutes' total operation :
Top skimmings.
Second skimmmings.
400 lbs., assaying 20 per cent.
.125
CC
เ
((
45
.6
65
450
((
673
เ
*
Clean ore, middlings.....550
Bottom ore. . . .
*Supplement to Ure's Dictionary, 1863.
CONCENTRATION.
153
When driven by men, the dolly has a handle or crank for
this purpose. If by machinery, the shaft of the dolly is
furnished with a cog-wheel. The rotating time after all the
sand has been introduced is about five minutes.
SEC. 41.
Aufermann's Dry Jigger.
Dry separation and concentration, in which moving air is
used in place of water, is subject to some difficulties; but in
mining districts destitute of water, as in Arizona, Sonora.
many places in California, etc., dry concentration deserves
attention. Various "wind separating apparatuses" have
been constructed on the principle of exposing the falling
stuff to the effect of moving air or wind in long canals or
chambers, provided with compartments. The simplest, but
most troublesome method, of separating gold from sand, is
that of blowing with the mouth, as is done by the Papago
Indians in Arizona. or as it was performed in early times in
California by many bankers and gold-dust buyers. In some
mining places of Spain, Belgium and Germany, where there
is no water, dry concentration and separation are performed
in machines to which fan-blowers are attached.
The weight of an ore particle loses a great deal when sub-
merged in water; but in a current of air the loss is very
insignificant. The difference in speed of falling of ore parti-
cles is also insignificant, and it is only the exposure of the
surface of each particle to the moving air which effects a
separation. The influence of the specific gravity is unim-
portant. The application of a steady blast of air seems to
be more suitable for separation into equal sizes than for con-
centration; but, although the specific gravity is of little
influence, the heaviest of equal size will always fall some-
what sooner, and permit a concentration.
Aufermann's concentrator is constructed on a better prin-
11
{
154
CONCENTRATION.
ciple. The separation depends on the greater or less resist-
ance of heavier or lighter particles in being lifted up, and on
the difference in speed of the free fall. Repeatedly exposed
to the same action, the heavier ore separates from the gangue
particles and concentrates on the bottom of the sieves. This
dry jigger is constructed on the same principle as the station-
ary jigger, (§38, B) with a piston from below. There are
three horizontal sieves, twenty inches by twelve each,
arranged in step-like form. They are enclosed air-tight on
all sides, except below. The bottom below the sieves is
movable, and connected with the upper box by leather all
around, like a bellows, with two valves, which are shut dur-
ing the upward motion.
The ore is introduced on the first sieve through a hopper,
and the shaft put in motion. The air, pressed against the
sieves, lifts the ore at each revolution, (from sixty to oue
hundred per minute) so that the separation takes place in a
short time. The upper stratum of refuse is drawn off, and a
new charge added, until sufficient concentrated stuff accumu-
lates, which is then removed. According to Pernolet, if
ore is subjected to dry concentration in the usual blowing
apparatus, the ore must be reduced to at least three-eighths
of an inch, but not less than to three-twenty-fifths of an inch,
(diameter) whilst Aufermann's jigger separates grains of
less than one-fortieth of an inch diameter.
The wind separator as used in Engis, (Belgium) contains
two ventilators, by which a steady current of air is pro-
duced, carrying the ore over a number of compartments.
The canal is about forty feet long, from nine to twelve inches
wide, and two feet high near the blowers, and nearly four feet.
at the end. The principal requirement to secure a good result
is, first, a steady uniform current of air, and, second, a uni-
form feeding.
CONCENTRATION.
155
SEC. 42.
Concentration of Ore-Sands and Slimes.
The concentration of fine sands and slimes is generally
performed on wooden or metallic inclined planes. The prin-
ciple on which the separation of assorted grains on an
inclined plane is based, consists in the resistance of a grain
particle, by sliding or rolling friction, to the impulse of the
water on the surface of the grain.
The sorting of sands suitable for tables cannot be executed
by sieves advantageously, and is best performed by the free
fall in moving water (§43, D). Sorting or sizing through
sieves yields classes of equal size of grain. Sorting through
moving or standing water gives different sizes of different
density-that is, equally-falling grains are obtained ($35, a).
Equally-falling grains are such as sink with equal speed, or
which fall the same distance in the same time. The labyrinth,
sluices, pointed boxes, etc., produce classes of equal-falling,
but not equal-sized grains; but in each class, according to
§35, a, the smaller grains are the denser and the larger the
lighter, so that a sifting of each sort would separate the
heavier ore particles from the lighter gangue. This pro-
cess, however, on account of fineness of the stuff, cannot be
carried out.
Equal-falling grains do not permit separation under water.
It is, therefore, important to convey a thin layer of diluted
stuff on the table.
nt
In this case the water will not strike all
points of each grain with equal speed, as it would in a
deeper stream; but the larger lighter particles will suffer a
stronger impact of water on their higher points than the
smaller ore grains, for the reason that in a thin water stratum
immediately on the table plane the water has less speed, on
account of adhesion, than in the upper layer. Consequently,
of the equal-falling grains, (for instance, sands from the first
box, $43, D) with a certain medium speed of the water,
156
CONCENTRATION.
depending on the inclination of the table, the larger gangue
particles will be washed off, while the smaller ore grains still
remain on the plane.
The inclination of the table and the speed of the water
have great influence on the concentration. If the table is
but little inclined, dense and light grains will remain; and if
too much inclined, all will be washed off. Most tables
receive an inclination of from six to eight degrees. Rough
planes for instance, canvas or blankets-require to be more
inclined than smooth planes. The dilution of the sand is
also important. A thick condition must be avoided, and is
much more injurious than too thin a one.
Although sorting is a condition of proper separation, still
a perfect concentration cannot be expected, not only because
of the impossibility of ever obtaining a uniform size, but
also because of the difference of shape, ($35, b) by which
the influence of specific gravity is modified. For this reason
the best concentrating apparatus will give a medium stuff
between the rich part and the waste, which will not be good
enough for extraction of the metal, but too rich to be thrown
away. The handling of such stuff may be profitable in one
place, but not in another, like California or Nevada, for
instance, unless it is effected in a simple way by machinery.
This is now done by small elevating wheels of four or five
feet diameter, by which the middle stuff is conveyed back on
the table, so that by this arrangement only two sorts come
from the concentrator-that is, a rich portion and the worth-
less tailings. But, notwithstanding these improvements, it is
in many cases advisable to regulate the concentration
directly for only two educts, and to dispense with the mid-
dling stuff by turning it either to the rich portion or to the
tailings, as the case may require.
Pulverization for the purpose of concentration is best per-
formed by stamps. All modes of crushing whereby the ore
is ground more than broken, are less suitable, because more
floating stuff is always produced.
The influence of specific gravity decreases with the increase of
CONCENTRATION.
157
the fineness of the ore particles, so that, in the condition of the
finest slime, the influence of specific gravity is almost noth-
ing. Hence the difficulty in concentrating such stuff.
Suitable crushing includes, as a matter of course, also such
arrangements as will serve to separate the different grades of
size, and in some degree to effect also a separation according
to specific gravity on the way from the battery. Leading
the stuff directly from the battery upon or into a concentrat-
ing apparatus, is a very bad method, resulting always in great
loss. There is only one case where a direct concentration
should be applied. This is the case of ore in which the par-
ticles are so small and disseminated in the gangue that the
finest crushing must be adopted in order to permit concen-
tration, provided, however, that very little or no clay occurs
with the ore. Free slime can be considered as a compara-
tively uniform stuff, suitable for concentration; but the
advantage of this uniformity is so much diminished by other
circumstances that fine crushing must be looked upon as a
necessary evil.
The nature of the ore must determine whether fine or
coarse crushing is required. It is frequently the case that
ore particles, and especially gold, are so small that they can
hardly be perceived. These minute particles will be set free
by a very fine reduction. The coarser the crushing, the
more of the fine mineral remains inclosed in the gangue, and
will be washed off; but, on the other hand, as before said,
the very finely pulverized ore sinks with difficulty, especially
if much slime is produced. In both cases a considerable.
loss must be expected; and this is the concentrator's
dilemma. He must try to make the best of it, and pursue a
middle course. Experience will show him how far the reduc-
tion can be extended advantageously. As a guide to what
degree of fineness the ore in question should be reduced,
experiments may be made with samples which represent the
average ore by pulverizing it to different degrees of fineness
and washing it in a horn-spoon or other suitable contrivance.
1. It has heretofore been impossible to draw a strict line
158
CONCENTRATION.
between what is understood under coarse and fine sand and
slime. Rittinger's scale is definite, and based on the free fall
of grains in water. Taking quartz, the speed of which per
second is-
0.125 meter, it represents coarse... sand of nearly 0.066 of an inch diameter.
middle fine "
0.062
0.031
fine
(C
0.016 "
0.005 "
(C
What is below 0.005 is termed slime liable to form a paste.
"Free slime" is less fine than "tough slime."
Gold quartz, in most cases, will give a better concentrating
result by being pulverized fine. There is not only the great
specific gravity of the metal, but also the gangue, to be con-
sidered. Quartz never produces such a muddy, and, for fine
gold, dangerous condition of the water as other earths.
It has been mentioned already that in treating gold quartz
with intention of direct concentration, no quicksilver should
be used in the battery. The loss of gold will increase, in
consequence of the amalgam formed. It is not so much on
account of the decreased specific gravity of a gold particle
when combined with quicksilver that the loss becomes
heavier, because it gains in absolute weight, but principally
on account of the property of fine gold to form voluminous,
sponge-like aggregations of amalgam particles, which are
light and so easily removed by a slight motion of the water,
that in most cases it escapes the notice of the prospector.
Considering that in general the heaviest gold is that which
remains in the form of amalgam in the battery, and which
would not have escaped the concentration, even if only blank-
ets were used for this purpose, there is no reason whatever
to collect such gold by means of quicksilver, since it must
remain on the blankets. The disadvantage of using quick-
silver in the battery is not only in the increased loss of gold
in concentration, but there is also a loss in time while clean-
ing the battery, and the exposure at the same time of the
valuable amalgam to too many hands.
Not injurious in regard to loss of gold is the use of quick-
silver in the battery, but still entirely needless, where the
CONCENTRATION.
159
whole mass of crushed rock is allowed to settle in tanks for
the purpose of direct amalgamation.
2. The question has been raised often in California
whether concentration should be carried out before or after
the amalgamation. In regard to gold ores, concentration
before amalgamation is indicated-a, when the ore is poor;
b, when the amalgamation of middle class ore is performed in
grinding pans, and c, when the ore contains auriferous sulphu-
Concentration after amalgamation should be adopted-
a, where ore rich in free gold is worked in grinding pans or
other amalgamators, and b, where middle class ore is treated
by amalgamation without grinding. But it is different with
regard to silver ores. Roasted silver ores can be amalga-
mated so closely as to render the tailings worthless; but this
is not the case with unroasted.
rets.
3. The subjection of unroasted silver ore to pan amalga-
mation in Nevada, (Comstock ore) is justified by several
circumstances. First, it contains gold which needs no roast-
ing; second, it is not rich enough in silver to repay the
expenses of roasting; and finally, it carries a considerable
proportion of silver glance, which is decomposed almost
entirely in the pan, so that only a portion of undecomposed
brittle silver ore, with nearly all the ruby silver which some-
times occurs, is left in the tailings. In regard to this unde-
composed silver mineral, the most rational treatment would
undoubtedly be concentration and roasting; but the quantity
of water which would be required to concentrate eight hun-
dred to one thousand tons of ore per day, which are crushed
at present from the Comstock lode, then the capital required
to build systematical concentration works, and the loss of at
least thirty per cent. of the silver ore, must be considered.
Under such circumstances, it appears that amalgamation in
pans, without roasting, and concentration afterwards, is the
proper way. The scarcity of water is then less injurious,
inasmuch as most of the valuable metal has been extracted
already by amalgamation, whereby the tailings are greatly
reduced in value, and consequently the loss less important.
160
CONCENTRATION.
The difficulty in concentrating pan tailings lies principally
in the very fine condition of the ore, which is more brittle
than the quartz, for which reason the finest slime is generally
the richest part of the tailings, though unfit for concentra-
tion. With the aid of slime separators, (§43) the separation.
of sand and slime is easily effected. This slime, as before
mentioned, is richer, often more than twice as rich, as
the sandy part; but it cannot be subjected to concentration
unless in a negative way, by washing off the finest part,
which will be found richer.
Crushing for the sole purpose of concentration offers the
advantage of a proper regulation of the quality and quantity
of the crushed stuff according to its nature, and suitable for
the adopted mode of concentration. In order to prevent the
flouring of brittle ore, the stamps in Europe are light,often from
eighty to one hundred and sixty pounds, especially if silver ores
are treated. This, however, would not answer on the Pacific
coast. It would not, however, be advisable to put up heavier
stamps than about five hundred and fifty pounds each.
Quantity must be subordinate to quality of the stuff to be
concentrated. It is very important that each particle of ore
should be discharged as soon as it is reduced to the required
size. To accomplish this, the first requirement is to have a
shallow trough in the battery—that is, to keep the dies from
one and a half to two inches below the screens, to arrange
the discharge on two sides, and to use screens with holes.
close together. In regard to the water necessary for the
discharge, see $26. If the ore requires to be crushed fine-
that is, finer than by means of the finest sieves-it is best to
construct a deep trough from five to eight inches.
If different kinds of ores are delivered to a mill for concen-
tration, and vary in regard to gangue, the quartzose ore
should be separated from that in which lime or clay prevails.
The two latter earths produce a great deal more slime and
mud, so that, under similar circumstances, the quartzose ore
can be crushed finer, if necessary, without losing more metal.
But such separation is not always advantageously performed
CONCENTRATION.
161
unless the difference appears in masses, or it is taken from
different mines, requiring only to be dumped separately. Of
more importance is the separation of various minerals, if
possible, if their cohesion is different and all have to be con-
centrated.
SEC. 43.
Assorting of Sands.
The feeding of the batteries must be very regularly per-
formed in order to effect a uniform discharge, which is a
necessary condition for the preparatory separation which
follows. It would not do to collect the stuff in tanks, as is
done with ore for amalgamation in pans, because in this case
coarse and fine sand and slime would be mixed, forming thus
a very unsuitable stuff for concentration. Not only must the
slime be separated from the sand which is produced in fine
as well as in coarse crushing, but the sand should deposit in
its course from the battery according to the different sizes.
and weight of the grains. For this purpose a system of
launders, or canals, are prepared, having different inclinations
and lengths, called the
A. Labyrinth.-This is always so arranged that the first
trough, in which the heaviest and largest part of the crushed
stuff deposits, is the deepest, narrowest, and most inclined-
say fifteen inches deep and about nine inches wide. The
next trough may be twelve, the third fifteen, then eighteen
inches wide, and so on. The same quantity of water will
assume a proportionally slower motion as it enters a wider
launder, and allow the sinking of such particles as could
not reach the bottom in the narrower. The inclination
decreases as the troughs grow wider, so that the last ones are
set level. The troughs are not arranged in one line, but
broken in different directions, as the room may require.
162
CONCENTRATION.
There must be also two sets of the same arrangement, so
that when one is being emptied, the stuff from the battery is
turned into the other. These troughs never can be so
extensive that all fine slimes can deposit. For this reason
there are generally outside of the building large tanks or
cisterns. Each trough (or several of them, of same width
and inclination) contains a separate class of stuff, which is
concentrated in the most suitable way.
There are now better methods than the labyrinth, by
which the slime is separated and the sand sorted in its course,
being conveyed by the water directly to the concentration
($43, D). The stuff for concentration is taken either directly
from the battery, or from agitators, in which the tailings are
discharged after being treated in settlers, (pan amalgama-
tion) or from piles of old tailings. In either case, the sepa-
ration of slimes must take place first, and is performed in
Slime Separators.-They are of different construction,
depending on the falling of the denser portion of the stuff
through an ascending current of clear water, whereby the
slime is carried upwards and out of the apparatus.
B. Borlase's Slime Separator is used in the United States
and in England. This apparatus consists of a funnel, with
the greater base upwards. At the point below, the funnel is
open, with means of regulation. A little higher is a circular
chamber, from which the clear water passes into the funnel,
(through holes in the funnel, surrounded by the chamber).
Inside of the funnel is a second one, somewhat smaller, but
corresponding in shape with the first funnel, so that a space
is created all around between the two cones. The inner
cone is covered with another short cone, the larger base of
both joining tightly.
The ore is introduced on the top of the inner cone, spread-
ing all around. The sand falls through the space between
the cones, through the ascending clear water from the cham-
ber below, while the slime is carried over the rim of the
CONCENTRATION.
163
outer cone. Admitting more clear water, and thus increasing
its ascending velocity, the quantity of the slime will be
changed by a greater proportion of flour sand.
C. Ph. Hofmann's Slime Separator.-Fig. 10, Tab. III, is
a vertical section. Fig. 11 represents the top view. This
machine, introduced in Hungary in 1836 at Ruszkberg, about
eleven years previous to the pointed boxes, separates the
slime very perfectly, and by giving more or less water in b,
and opening the cock or gate at c, more or less, the separa-
tion can be regulated, so that finer or denser slimes can be
obtained. The crushed stuff enters the funnel, d, through
the launder, a. In sinking down to the slit, e, the ore parti-
cles find time to spread and separate. Passing through e,
they meet a current of clear water towards h, and upwards to
f. The clean grains sink through the current, being carried
out at h, into the trough, k, and from thence to a sifting
arrangement. The slime is carried upwards by the ascend-
ing water, and through the conduit, m, to some concentration.
This apparatus was used by the writer in Transylvania for
separation of gold ores. Through the openings, n, n', two
sizes of the ascending stuff are separated.
D. Rittinger's Funnel, or Pointed Box (Spitz-kasten).—
The funnel boxes are rectangular pyramids, with the base
upwards. They are designed to replace the "labyrinths,"
for the purpose of assorting the sands for concentration
directly from the battery. The battery sands are too fine
for sorting by sieves; the labyrinth is an imperfect and
troublesome sorting. The pointed boxes are the best of all
contrivances for this purpose. The stuff flows from the bat-
tery through several of these boxes of different size. Each
delivers a certain size of grains directly to the concentrators.
In this way the sands can be separated into different grades
of fineness, with very little expense, in simple apparatus,
*(Spitz-kasten) pointed box, (Spitz-trichter) funnel box, signifies the same
machine. The latter refers to a smaller size, separating the coarsest grains close
at the battery.
164
CONCENTRATION.
without the help of hands. The transportation of sand from
the battery to the concentrator is performed without expense.
These boxes offer also the advantage of getting rid of a
surplus of water, which would interfere with concentration.
The sands are obtained from the boxes always in the required
state of dilution for the tables.
The principle is the same as with the labyrinth. The first
box is narrow. This causes the water to flow swiftly, so that
only the coarsest grains are permitted to sink, while the bal-
ance is carried into the next wider box, where the same
quantity of water spreading, assumes a slower motion, so that
the next finer sand is separated, and so on.
Figs. 12 and 13, Tab. III, represent a pointed box. Fig.
12 is a vertical longitudinal section; 13, a vertical cross sec-
tion. The stuff flows from the battery, or from a sifting
apparatus at a, into the box. The sinking grains concentrate
at the point o, and flow out through the ascending conduit, o',
into the trough, p. The finer stuff which could not resist
the current of the water is carried over the spout, b, into the
next larger box. The conduit, o', ascends, in order to coun-
terbalance the water pressure inside the box.
To obtain all its advantages, theoretical and practical
experience must be taken into consideration in constructing
the pointed box.
The width of the single boxes is important. It depends on
the quantity of stuff which enters the box in a second, and
on the coarsest and densest grains in it. According to expe-
rience, the first box by which the coarsest part of coarse
crushing is to be separated, must receive one-tenth of a foot
width to each cubic foot of stuff flowing per minute. Each
of the next following three boxes receive twice the width of
the preceding.
If, therefore, such an arrangement were intended to sepa-
rate ten cubic feet of coarse crushing per second, the first
box should receive 10X1-10-one foot width and the whole
arrangement of four boxes:
1, 2, 4, 8 feet width, and
3, 6, 9, 12 feet length.
CONCENTRATION.
165
The depth is given by the inclination, which, measured
from a horizontal line, is fifty degrees. This inclination is
given to the sides of the width. The conduit, o', can be
formed also by a pipe, (i, Fig. 14, Tab. III) which, on the last
boxes, with fine sand, stands vertical. The pipe must be
shorter with coarser sand.
If it should be necessary to obtain a thicker stuff for
the concentrator, there must be a valve at o, which opens at
short intervals. The connecting troughs between two boxes
(d, Fig. 18, Tab. III) widen towards the larger boxes, and
must be sufficiently inclined, so that no sand can deposit in
them. The coarser the sand, the more inclination. The
boxes are not always close together, and in this case the con-
veying troughs are narrow, discharging on a distributing
board of the next box.
The conveying troughs receive a square section. It is cal-
culated that five square inches will answer for each cubic
foot of stuff per minute. If, therefore, for instance, seven
cubic feet of diluted stuff flows per minute through the
trough, it must have 7X5=35 square inches, about six by
six in the clear.
The inclination of the conveying trough must be in each
six feet at least-
For coarse sand (§42, 1).
"middle fine.
1 to 13 inch.
3
I
1
((
fine...
((
slime..
(C
3
8
66
This inclination refers to galena ore with not over five per
cent. of galena.
The outlet of the pipe (i, Fig. 14) is regulated by mouth-
pieces, of which there must be several of different sizes.
Once regulated, there is no other work to be done, except to
watch the regular flow, as by some accident the conduit may
become choked. For such accidents, the larger boxes are
provided with a rod in the centre, on the lower end of which,
close above the opening, are two little wings. If the saud
or pulp should accumulate by neglect of the watchman, the
166
CONCENTRATION.
rod is turned until the stuff becomes loose enough to be
forced through.
The percentage received from boxes of the dimensions
described is as follows:
From the first box..
"
แ
second box.
แ
(
third box.
((
((
fourth box.
•
40 per cent. sand.
28
((
66
"
.18
((
"
((
.10
((
"
(6
So that the loss is not more than from four to six per cent.
It sometimes occurs that several stamps have to be arrested,
in which case the supply of crushed stuff is diminished. It
is then necessary to replace this deficit by water. But if a
varying supply depends on circumstances that cannot be reg-
ulated, or the deficit cannot be regulated by water, there are
other means to keep the fluid in the normal condition.
For this purpose, each box is provided with a movable long-
itudinal board. It is sufficient to make this board from twelve
to eighteen inches wide. In proportion as the supply of
water is less, the dividing board is moved towards one
side. If, for instance, the supply should decrease to half of
the normal quantity, the board is placed in the middle of the
box, and all the stuff must enter on one side. The active
part of the water reaches only a few inches below the sur-
face, so that the dividing board need not reach to the bot-
tom.
In Schemnitz, (Hungary) for crushing twenty tons in twen-
ty-four hours, the boxes have the following dimensions:
1 box 6 feet long, 2 feet wide, 4 feet deep.
23+
{{
9
tt
5
แ
6
(C
((
Յ
เ
12
แ
9
it
แ
8
((
4
66
16
66
((
15
(C
((
10
((
The first box gives 40 per cent. of sand.
second
แ
third
fourth
66
22
20
(
(C
(C
(6
((
(C
(C
12
แ
In case there should be a great quantity of sand in the
flow from the battery, the pointed boxes receive a partition
CONCENTRATION.
167
crosswise, one or two feet below the water surface, and reach-
ing to the point of the box, whence two conduits carry the
sands separate from each compartment. The first half gives
two-thirds, the second one-third, of the depositing sand.
At least two five-stamp batteries are required to make use
of the funnel boxes. If the flow from the batteries is much
less than ten cubic feet per minute, the discharge of the
single boxes would be so diluted that the stuff would not be
fit for concentration, and the application of mouth-pieces, by
which the discharge is kept very thin, would cause irregu-
larity by choking.
In the Harz, there are several arrangements of funnel
boxes. One is of the above description; another com-
prises four systems of a number of small boxes, (Trichter
Apparat) made of zinc. The arrangement is shown in Fig.
9, Tab. III, in a top view. The first two boxes, a, a, are
narrow and oblong; then follows three other boxes, square in
section, two feet ten inches each side, b, b; finally, two rows
of four boxes, c, c... c, in which the stuff divides. The
depth of all is the same-twenty inches. By means of gates,
each system can be shut off if required.
The small boxes could be advantageously applied for sizing
the stuff or tailings of unroasted ores from the pan amalga-
mation if concentration is intended; but, in order to obtain
a regular work, there should be a large agitator, with a con-
tinual discharge into funnels, which should be proportioned,
in number and size, to the quantity of tailings. A common
recciving agitator is necessary, because the discharge of the
tailings from the settlers is periodical in most mills. Where
the pulp is excessively diluted in the settlers, the agitator, if
not large enough, must be provided with a trough at the
top, to convey away the overplus of water. A modification
of the funnel box is the
E. Spitz-Lutte.-This apparatus resembles very much the
slime separator ($43, C) but is applied like the funnel boxes,
principally to sizing the sands, conveying at the same time
168
CONCENTRATION.
clear water from below, by which the sand is freed from slime
or from the finer sand. The same classes of sized sands are
obtained as from the funnel boxes, but under certain circum-
stances a "Spitz-lutte" is preferable for the reason that the
speed of the flowing sands can be regulated, so that a set of
two or three of these boxes which are prepared for four bat-
teries, will answer also for three if regulated accordingly.
The Spitz-lutte is a descending and ascending conduit of a
rectangular section. With a horizontal line the conduits
make an angle of sixty degrees. These boxes are represented
on Tab. III, in Figs. 14, 15, 16, 17 and 18. The dimensions
are prepared for a battery supply of ten cubic feet per min-
ute. a, shows the vertical boarding at the sides of the con-
duits formed by the inclined walls, b, b'. The upper walls, b', b',
form a movable wedge. The box is kept together by the
wooden rails, c. The troughs, d.., widening at the mouth and
outlet of the apparatus must have sufficient fall to prevent
the settling of sand. With more boxes in a set, or if they are
of considerable size, it may answer to have movable partitions
on d..
The discharge funnel, e, communicates with the horizontal
wooden pipe, i, both ends of which connect vertical pipes, "'.
The funnel blocks, f, (Figs. 14 and 18) have an inclination of
45° to 50°, leaving an opening two inches square at the bot-
from one-half to three-quarters of an inch diameter in the
is
tom, connecting with the pipe, i. The discharge pipe, i",
clear. In case the pipes should get choked by accident, the
cleaning can be effected by removing the plugs, g, g.
In order to change the section of the conduits, in case it is
desired to run more or less battery-stuff, the wedge, b', b', is
provided with a set-screw, h, by which it may be raised or
lowered. The motion of the wedge must be steady and uni-
form. There are, therefore, guides (k, Fig. 17) fastened to
the sides, a, of the box. The wedge should not set directly
against the sides, as the water would flow between the wedge
and box side; there is, therefore, a leather strip tacked to
the edges of the wedge. The leather strip (1, Fig. 15, 17) is
CONCENTRATION.
169
pressed by the water against the side of the box, forming
thus a tight packing. When the flow of the pulp is constant,
the packing can be obviated by attaching the wedge, U', firmly
to the sides. This is especially advisable with the last and
largest slime box, in which a slower flow in not injurious.
Three feet is sufficient for the length of each conduit, but
the width of its section, that is, the perpendicular distance
between the inclines, b and b', ought not to be over from three
to six inches on coarser stuff, and not over fifteen inches on
slimes.
Having large sections of the boxes for slimes, the width
requires an inconvenient proportionate height. This can be
avoided by dividing the box lengthwise so that each compart-
ment receives its own discharge-funnel, e. If necessary,
there may be three or four compartments in the box.
The battery pulp flows through the trough, d, into the con-
duit. When it has arrived at the lowest point, the coarser
grains separate and sink through the funnel, e, into the pipe
i, whence they are conveyed by the clear water through i",
directly to a concentrator. A short india-rubber hose, in
place of i", would probably answer just as well or better than
an iron pipe, as in case of some impediment in i, the hose
needs only to be lowered, and the accumulated sand will be
forced out.
The finer sand, which cannot sink through the ascending
clear water, is carried up the ascending conduit and led into
the next larger box, and so on. At i, are kept mouth-pieces
of different size to regulate the flow of clear water into e and
i", upon which also the size of the sand is dependent in some
degree.
SEC. 44.
Feeding Boxes.
It occurs very often that tailings or other material cannot
be conveyed directly to concentrators, but accumulate. What-
12
170
CONCENTRATION.
ever the construction of a concentrator may be, a regular
feeding in a proper state of dilution is an important condition,
otherwise an increased loss would be a necessary consequence.
There are many different contrivances for sands and slimes.
A slime-feeder cannot be prepared without motion, and
requires the stuff to be sufficiently diluted. For sands a very
suitable feed box is
A. The Stationary Feed-Box.-It is represented in Tab.
IV; Fig. 9 shows the vertical central section of Fig. 10,
which is a cross section of Fig. 9 on the line, x, y. Fig. 11,
Tab. IV, shows the block, g, of Figs. 9 and 10 on a larger scale.
The box has a bottom, a, a, which is inclined both ways,
towards the front and both sides. In the middle of the front
b, at the bottom, is an opening, e, for the discharge. g, is a
block to regulate the water which is introduced for the pur-
pose of carrying out the sand. The block is constructed as
shown in Fig. 11. It is twenty-three inches long, six inches
wide, and three inches thick. On one flat side a canal is.
made, as shown by c, down to h. Half the distance above the
end, h, on each side of c, two canals, i, are made as represented,
first ascending in a fork shape, turning then downwards and
joining in k.
The canals, c and i, are cut out one and a quarter to one and
a half inches deep, and a hole bored through in h. The open
cut side of the block is screwed on to the backside, b', of the
box, so that the canal is shut up from all sides, communicat-
ing inside only by the opening, k, which is placed exactly
above the joint edge of the bottom, a, a. There is another
wooden pipe, m, triangular, the edge being turned upwards.
This pipe is so fixed to the block, g, that the canal, c, is con-
nected with it. The pipe is inclined and only three-sixteenths
of an inch above the roof of a, all the way to e.
When the box is filled with stuff, the place below m remains
free, at least on that part of the roof or edge of the bottom
which is nearest to m. The water, introduced into c, passes
through m, into the trough, o, but if partially checked by the
CONCENTRATION.
171
cock, p, the water must rise in the canal, c, and flow through
i (Fig. 11) into the box below, m. On its way it has a ten-
dency to spread on the inclined bottom, thus constantly car-
rying the sand down, through e, into the gutter, o.
The
workman has it entirely under his control to let out more
or less sand, as may be required, by shutting the cock, p,
more or less. He can at the same time regulate the degree
of dilution. This apparatus is very handy, requiring only to
be charged before it becomes empty. The feeding is regular
and continuous, provided the sand is not mixed with foreign
matter or clay lumps, but sifted or sized.
A better contrivance for sands and slimy stuff, but requir-
ing motion, is
B. The Rotating Feeder-(German, Dreh-Gumpe).—This
apparatus is shown Figs. 12 and 13, Tab. IV. The wooden
frame, constructed of four by four timber, on which two hop-
pers, a, and a circular trough, b, rest, is not represented. The
vertical shaft, c, to which a conoidal disc, d, is fastened, is
kept in slow rotating motion by an endless screw.
The sand is introduced into the hoppers, a, which stand
opposite each other, and of which only one is shown in the
drawing. As there is no bottom attached to the hopper, the
sand falls on the disc, d, which slowly glides beneath. The
quantity of stuff carried by the disc is regulated by the scrap-
er, e; the nearer it is brought to the disc, the thinner the
layer of sand. This disc is furnished all round with radial
sheet-iron strips, f, between which shorter pieces are fast-
ened, in order to distribute the water more regularly.
The water is conveyed with several feet head through the
iron pipe, g, (one inch diameter) of which there are also two
in number, arranged as shown in Fig. 13. The circular gut-
ter, b, is inclined towards the spout, h, and has a rim, i, of
sheet-iron, to prevent splashing over by the jet of water.
From the spout the stuff is carried through an inclined cylin-
der sieve to keep undissolved lumps or chips, etc., from the
concentrator.
172
CONCENTRATION.
At Joachimsthal (Bohemia) one rotating feeder of the above
description, with two hoppers, making six revolutions per
hour, supplies two rotating buddles, or two self-discharging
percussion tables, with six tons of stuff, with very regular
feeding, in twenty-four hours, using 1.88 cubic feet of water
per minute.
Concentrating Machines.
The concentrating machines are either stationary, percus-
sion, oscillating and shaking-tables, or steady-moving con-
trivances.
SEC. 45.
Stationary Concentrators.
This class is very numerous. The fundamental construc-
tion of all is a simple wooden box, of from ten to fifteen feet
length, twenty inches to four feet width, and from one to two
feet depth, having an inclination of from twelve to eighteen
inches in the whole length. Modifications of size, shape and
treatment have produced the different terms. The stuff to
be treated in these apparatuses is often unsized, so that con-
centration and at the same time sorting is effected; but, on
account of this double purpose, the concentration must be
repeated several times. To the stationary concentrators
belong-
A. The Hand Buddle.—It is represented in Fig. 15, Tab.
IV. This apparatus is extensively used in lead mines for
coarse sand. There is a separation of the finer stuff, and also
a concentration of the coarse, effected. Above the head of
the buddle is a box, or a platform, a, from which the washer
draws a charge of about half a cubic foot of stuff into the
CONCENTRATION.
173
buddle, which is from twelve to fourteen feet long, and twen-
ty-two inches wide and deep. The sand is spread equally,
and raked towards the head, while clear water from c, carries.
the lighter part down. The water, e, is regulated by the
holes, f, in the front board.
>
The clear water is sometimes conducted directly on the
platform, in which case no compartment, c, is made. The
workman rakes the stuff on the platform, using a sieve, b. to
prevent impurities from entering the buddle, while the
washer rakes the sand in the buddle until it is nearly filled,
taking about an hour's time.
The buddle receives one inch fall to every foot in length.
The openings, f, of which there are five in number at equal
vertical distances, are one ich in diameter each. The work
requires about one cubic foot of water per minute. The
poorer the sand, and the better it is assorted, the more water
can be admitted.
The deposit is then divided into three parts. of which the
"head" is the richest, containing the least proportion of slimes.
This head is taken out to the line, g, sometimes less. The
next smaller part, the "middle," is about as rich as the origi-
nal stuff on the platform where it is thrown. The last part,
from h to e, (the "tails ") is again washed on some other con-
trivance. In many places there are three of these buddles
near together, so that the second receives the heads from the
first, and the third one finishes the heads of the second bud-
dle. The heads in the third are washed with more care, but
in the same way as in the first buddle.
There is with the hand buddle the same disadvantage as
with the round buddle, concave buddle or percussion table,
that the head by the accumulation of heavy stuff changes the
original and proper inclination, causing an irregular separa-
tion, so that the head becomes poorer. In this respect the
percussion table has the advantage of being capable of chang-
ing its angle, so that the inclination of the head can be regu-
lated as the work advances. On all tables where the concen-
trated stuff accumulates to several inches, the use of rakes is
preferable to that of brooms.
174
CONCENTRATION.
B. Sleeping Tables.-These tables are similar to the hand
buddle, but wider. They serve for coarse fine sands and free
slime. The table is a box, eight to twelve feet long, and four
to five feet wide. The sides are from twelve to eighteen
inches high. The lower front of the inclined table has peg-
holes in different heights. The sand flows at the head in a
proper state of dilution into the box from a distributing board,
and is raked against the current. In proportion as the bot-
tom is covered with the denser stuff, the peg-holes are grad-
ually stopped, till six to eight inches of ore are deposited. The
. upper part of the head is generally washed over once more,
giving then a suitable schlich. The middles are washed over
separately, by which a head is obtained and washed together
with the heads of the first operation. The tails are delivered
to the original stuff.
The diluted stuff must flow over the table in a thin stratum,
because only in this condition can a proper concentration be
effected. The finer the sand the more it must be diluted.
The speed must correspond to the sort of sand.
By experience, the most proper fall in the whole length of
the table of twelve feet is, for
Coarse sand…….
Middle fine.
Fine.
Slime.
20 inches or 8 degrees
15
10
6
"L
6
(
แ
i
In order to preserve the original inclination during the
operation, the peg-holes must be shut in proportion as the
work proceeds. This and similar tables are often charged by
spreading the stuff with a rake on a platform above the head
of the table, which causes a very irregular distribution, and
ought to be replaced by feed boxes (§44).
The Rack, or hand-frame, is composed of a frame with a
smooth floor. The table is from two and a half to three feet
wide, six to nine feet long, and on both ends provided with
pivots, susceptible of being turned to the right or left on its
inclined long axis. In operating on this table, the slimy ore
to the extent of about twenty pounds, is placed on the table
CONCENTRATION.
175
and distributed equally over the head, by means of a rake,
admitting clear water. The schlich remains on the upper
part of the table, whilst the muddy water falls through a cross
slit at the bottom into a receptacle. When the charge of ore
has been thoroughly raked, the table is turned on its axis,
until it is brought into a vertical position and the deposit on
its surface washed into a box. The operations of this table
are similar in other respects to those of the sweeping table.
C. Sweeping Tables are mostly used for concentration of
middle fine sand, fine, and slime. These tables are from twenty
to thirty feet long, and from three to four feet wide, boarded
on the long sides from four to six inches high. Ore containing
blende or spathic iron requires a table thirty feet long. The
bottom must be perfectly plane and smooth. The concentra-
tion is performed interruptedly-that is, as soon as a thin
layer of ore is washed, the table must be cleaned for another
charge. The slime is conducted from some agitator or feeder
on the table, and the feeding stopped when the stuff reaches
the lower end of the table. Clear water is then admitted,
and the slime, by means of a broom, washed against the
head; but very gently, or not at all, if tough slime is oper-
ated upon. When the ore appears clean, a slit at the end or
half the length of the table is opened, and the concentrated
ore, or schlich, swept into a box beneath. The sweeping
table gives a very good result, but the operation is slow, and
they undoubtedly give place to the superior self-discharging
rotating buddles. Fig. 1, Tab. VII, represents a sweeping
table of a smaller size.
The average inclination of sweeping tables is-
For sands.
(C
slimes.
10 to 12 degrees.
5" 6
The quantity which can be washed advantageously of
diluted stuff per minute is-
Sands...0.3 to 0.5 cub. ft., cont'g fm. 6 to 10 lbs. sand.
Slimes..0.08 0.12 **
0.28" 0.78"
(4
*
176
CONCENTRATION.
Twelve feet long, by four feet width, seems to be the most
proper size. The concentration of one charge takes eight
minutes in all. It requires about three times as much clear
water as diluted stuff.
D.
The Round Buddle.-This machine serves to concen-
trate slimes and fine sediments on a circular bottom, inclined
towards the periphery. The machine is represented in out-
line by Fig. 4, Tab. IV. The conical bottom, a, formed of
wood, is sixteen feet in diameter. (There are buddles of
twenty feet diameter.) On this the stuff is distributed. b,
is the cone supporting the upper part of the feeding appa-
ratus; e, a funnel, perforated with four holes, and furnished
at the top with an annular trough; f,ƒ, are arms, carrying
two brushes, balanced by the weights, g, g; h, is a launder
for conducting the stuff into the funnel, c, from which it passes
through the perforations, flows over the surface of the fixed
cone, b, and from thence towards the circuinference, leaving
in its progress the heavier portions of its constituents, while
the surface is constantly swept smooth by means of the
revolving brushes. By this means the particles of different
densities will be found arranged in concentric circles. The
arms usually make from two and a half to four revolutions
per minute, and a machine having eighteen feet in diameter,
will work up from fifteen to twenty tons per ten hours.*
With regard to the statement of working fifteen or twenty
tons in ten hours, it may refer to a superficial preliminary
concentration, combined with a considerable loss. The dis-
advantage of this buddle is the constant change of the incli-
nation, which produces an unequal speed of the water, and
consequently an irregular settlement of the ore.
E. Concave Buddle.-Contrary to the round buddle, the
bottom in this machine is inclined from the circumference
towards the centre, forming thus a funnel-like bottom. On
the centre shaft is a box which receives the slime; with this
*Supplement to Ure's Dictionary.
CONCENTRATION.
177
box there are four arms connected, which carry the slime to
the periphery of the buddle. The speed of the arms must
vary with the nature of the stuff to be operated upon; for
sands, eight revolutions per minute have been found sufficient,
but for fine slimes from fourteen to sixteen revolutions are
necessary in the same time. This buddle works better than
the round buddle, giving an extensive area on the circumfer-
ence for the heads, and thus admitting of the separation of a
greater bulk of sands. The area over which the slime is dis-
tributed diminishes towards the centre, while the water com-
paratively increases in quantity and velocity, sweeping off a
proportionate quantity of lighter matter associated with the
ore. The buddle is eighteen feet diameter, and has an incli-
nation of about six degrees.
An experiment on slime of argentiferous lead ores gave the
following result :
The slime before concentration assayed 6 per cent. of lead.
The heads of the buddle, 3 inches deep, 22 wide-12 per
cent. of lead, and 30 oz. of silver per ton of lead.
The middles, 1 inches deep, 18 inches wide-63 per cent.
of lead, and 42 oz. of silver per ton of lead.
3
I
Tails of the buddle, 1 inches deep, 18 inches wide-3 per
cent. of lead, and 55 oz. of silver per ton of lead.
Castaways, 1 inches deep, 18 inches wide-1 per cent. of
lead.
F. Blanket Tables.-Blankets for the purpose of concen-
tration are extensively in use, especially in the California
gold quartz mills. In most of the mills the heaviest of the
gold, that part of which, on account of its coarser con-
dition, is sure to remain on the blanket, is retained as amal-
gam in the battery. If, therefore, blankets enjoy the con-
fidence of the millmen for saving the finer part of gold or amal-
gam which escapes the battery, they might just as well do
the whole and save the trouble of cleaning the battery. The
blanket is a very old gold-saving instrument, and certainly an
effective one, if properly attended to. The mining or sluice-
blanket manufactured in California is of a superior quality,
178
CONCENTRATION.
usually twenty-four inches wide and sixty feet long, from
which the suitable length is cut. One side is long-haired,
the other short-haired. There is also other stuff in use, coarse
linen, gunny bags, etc.*
The great density of gold (=16 in average) permits of less
care in its concentration than other ore. It admits the use
of more water, and the tables can be set more inclined. Very
fine gold is troublesome to save, but cannot be compared with
very fine silver ores in this respect.
A gold grain of one-tenth of an inch diameter is equal fall-
ing with a galena grain of one-fifth, or with a piece of quartz
one inch in diameter.
The troughs for blankets are from twelve to fifteen inches
wide, and from ten to fifteen feet long. The sands from the
batteries are sometimes much diluted, in order to be distrib-
uted on three or four troughs per battery; in many cases
there are only two troughs used, or one. Four troughs are
preferable to three, for the reason that when the blankets
from one are removed for the purpose of washing them, the
sand can be turned on the other three troughs so that each
receives only one-third more for a short time, till the blankets
are washed. The best arrangement is with four troughs, .
two always in use alternately.
Generally there is a second and third row of troughs join-
ing the first, so that there are twenty-four to thirty-six feet,
and even as high as sixty feet, length of blankets.
The sides of the troughs are only one and a half to two
inches high. The blankets are laid so that the sides of the
trough are also covered, or better when the sides of the blan-
ket are rolled up from both sides as much as the width of the
blanket and of the trough allows. It is better to lay the
long-haired side down, so that the sands flow over the short-
haired side.
The first row of blankets are taken off and washed, accord-
*According to careful comparative experiments, made under direction of L.
Janin, blankets under similar circumstances save more valuable matter than gunny
bags.
CONCENTRATION.
179
ing to the richness of the ore, every ten or twenty minutes,
or every hour; the second row only half as often; the third
row twice or once a day.
The inclination of the blanket troughs is from ten to fifteen
degrees. If, besides the free gold, sulphurets occur in the
rock to which no attention is paid, or which are intended for
a regular concentration and conveyed through pointed boxes
for the purpose of assorting, the troughs must be more inclined
than with quartz free from sulphurets. Accumulation of sand
indicates either not sufficient fall, or want of water. Too
much water is injurious.
The first blanket or blankets contain about seventy to sev-
enty-five per cent. of the free gold obtained by blankets. For
this reason they ought to be washed separately in a box. It
is also best to carry these blankets from the trough to the
box in buckets, and never to take them off while the sands
are running.
The blankets retain a great deal of sulphurets, iron and
sand, so that the blanket stuff is comparatively poor. For
this reason it is subjected to concentration on tables (in
Europe) similar to sweeping tables, (§45, C) but only from fif-
teen to twenty-four inches wide and twelve feet long, inclined
from ten to fifteen degrees. By means of a feeder, (§44, 4)
the blanket stuff is conducted very regularly over the dis-
tributor, and washed, as described with the sweeping table.
Poor stuff is treated twice on the same table. From the con-
centrated gold sand, the gold is extracted by hand with
wooden pans, by a singular percussive motion, and then
amalgamated.
In California, the blanket sand is amalgamated directly
either in Knox's or other grinding pans, with addition of
quicksilver, and with or without application of heat; or
there are troughs with a half-round bottom from twelve to
fifteen inches, by six to eight, arranged in step-like order,
one below the other. The quicksilver covers the bottom
of these troughs, of which each has a roller, with roller
pins or stirrers. By these stirrers the blanket sand is
180
CONCENTRATION.
carried through the quicksilver, and the free gold is taken up
by the mercury.
In place of the gold concentrating tables, horizontally-mov-
ing canvas tables ($48, E) separate the free gold perfectly.
For silver ores, the density of which is very much less
than that of gold, blankets are very ineffective, because these
minerals are sooner and consequently more finely crushed
than the quartz, and assume, at the same time, an unfavora-
ble shape. Peculiar circumstances, however, may sometimes
require their use, as, for instance, in the Gold and Six-Mile
Cañons in Nevada, where from six hundred to eight hun-
dred tons of tailings flow down every day. These tailings
carry not only gold amalgam, but also silver sulphurets. In
order to save of that valuable stuff as much as possible, in
absence of a better contrivance, blanket troughs are put up
from five to six miles along both cañons. What may deposit
in two, three or six hours, is washed in wooden tubs, and the
stuff delivered to the mills, where it is amalgamated in pans.
With respect to self-discharging blankets, see $48, E.
SEC. 46.
Percussion Tables.
The concentration on percussion tables depends not only
on the action of the water upon the surface of the mineral
particles on an inclined plane, but also on the action of the
percussion which the table receives. The forward motion of
the table is generally slow. This and the current of the
water carries the mineral more or less down the incline; but
at the instant when the table swings abruptly back, all the
particles assume the tendency to follow that motion-the
denser more, the lighter less. This motion, by the striking
of the table against some fixed substance, is suddenly stopped,
while the ore particles, not encountering a fixed hindrance,
follow the imparted back motion, slide on the table or on the
deposited ore from their resting point backwards, so that the
CONCENTRATION.
181
heavier stuff is always retained at the head of the table,
whilst the lighter earthy part, on which the action of the
water has more influence, is carried over the table down-
wards.
The percussion tables are of great importance for the con-
centration of sands, but at the same time they answer also
for free slimes, although the latter, especially when tough,
are more advantageously treated on rotating buddles. Oper-
ating on slimes with percussion tables, the concussion must
be slight and the swing short.
A. The German Percussion Table.-As Rittinger's table
does the same amount of work in a great deal shorter time,
suffering the same or less loss in concentration, it is sufficient
to give a sketch of the common percussion table, as shown in
Fig. 5, Tab. IV, in order to obtain a clear idea of its con-
struction. a, is the table, nine feet long, and from four to
five feet wide. The floor must be made smooth and level, on
a strong frame. It is suspended on four chains, b, c. The
chains, c, a portion of which is often replaced by rods, are
fastened to a roller, d, between the two uprights. By wind-
ing the chain upon the roller, the inclination of the table can
be regulated. Below the table, fastened solidly to the frame,
is the percussion rod, e, the head of which is from five to six
inches square. It strikes against the percussion block, i, which
requires to be stout and firm.
The table, when in rest, does not hang perpendicular. The
more the chain, b, departs from a perpendicular line, the more
effective is the percussion. The iron cramp, g, allows of
adjusting the chain for that purpose. h, is a pushing rod, in
connection with the movable fork, k, moved by the cams of a
revolving shaft. 7, is a feed-box, and m, represents the dis-
tributing board. The ore is placed either into 1, to which
also a current of water is conveyed, or it comes directly from
a sizing apparatus upon the board, m, whence it is distributed
evenly over the surface of the moving table. The workman
uses from time to time a light rake, to keep a smooth uniform
182
CONCENTRATION.
surface of the ore, which deposits at the head more than
elsewhere. This changes the inclination. For this reason
the workman must raise the chain, c, a little as often as may
be required. When the table is charged to a depth of six or
eight inches with washed ore, the motion is stopped, and the
deposit divided into three parts, each part removed sepa-
rately, and re-washed on the percussion table in the same
way. Of the second concentration, only the head is suffi-
ciently concentrated. The other parts from both concentra-
tions require a great number of manipulations-another
reason for giving the self-discharging tables the preference.
On the percussion table, the sand must likewise move with
such a velocity, and in such a thin layer, that the coarser and
lighter particles are carried off, while the smaller and denser
ore grains remain on the table. This requires a certain
quantity of diluted pulp, and a definite inclination of the
table. Quantity and inclination must decrease with the
increase of the fineness of the pulp.
A table of five feet width requires per minute-
Of diluted sands..
And for sands..
slimes.
slimes..
..0.5 to 0.7 cubic feet.
.0.10
" 0.17
((
(6
5 to 8 inches fall per 6 feet.
2" 3
For middle stuff, the inclination must be between these two
extremes. The amount of sand in the pulp has an important
influence on the concentration.
One cubic foot of water can contain-
Of sands... . .
"slimes
The number of strokes per minute-
20 to 40 pounds.
5" 10
(C
For sands with elastic percussion blocks... 12 to 16
(6
{{
แ
stiff
แ
slimes
(
(C
The stroke—
For sands (the coarsest) is.
แ
slimes
แ
(6
.40 50
..60
80
12
inches.
4.8
66
•
CONCENTRATION.
183
B. Continual Percussion Table (Rittinger's).—The differ-
ence between this self-discharging and the common percus-
sion table lies principally in the percussion, which is applied
on one of the long sides. On the common table, the denser
particles move backwards, whilst the lighter particles are
carried down in the opposite direction by the water. On
the self-discharging table, all the grains follow the impulse of
the water; but the denser move more slowly, on account of
their friction on the table. From this downward motion.
they are diverted to a transverse one by the percussion,
which again does not act as strongly on the lighter earthy
particles, so that, as shown in Fig. 8, Tab. V, the light min-
erals, a, will follow nearly straight down in the course of the
water, the densest, c, the diagonai, and the ore of less grav-
ity, b, the middle course, as indicated by the dotted lines.
By this means the separation of the orey matter from the
earthy is effected uniformly and continually. The separation
of the different ores on these tables is very perfect.
The first experiments were made on a table which had
only one side, d', the other, d, was not attached, so that the
ore had to be discharged on the long side at d, and the refuse
in front; this, however, would not answer, until A. Palmer,
in Hungary, shut up the long side, d, changed the quantity
of charged ore and the intensity of percussion, and succeeded
in separating all on the front side with a high degree of
purity. In Hungary and Austria these tables are introduced
almost everywhere in place of the common percussion tables.
Tab. V, Figs. 7, 8, 9, represent Rittinger's table. Fig. 7 is
the front, 8 the top, and 9 the side view. The table, a', is
generally eight feet wide and eight feet long, but divided
longitudinally in the middle by d', forming thus a double
table. It is suspended on four iron rods, e, and has an inclined
position, as seen in Fig. 9. The motion is imparted to the
table by the rods, e, connected by the perpendicular rod, f,
with the block, g, on which the cams of the shaft strike. The
rods, e, e, are fixed to the nuts, g', shown on a larger scale in
Fig. 11, which moves on the screw by turning the head, g".
184
CONCENTRATION.
By this means the stroke can be lengthened or shortened.
The horizontal screw is bolted to the percussion rod, h, which
forms a part of the frame of the table, and strikes against the
percussion block, i, Fig. 7 and 8. The percussion is produced
by the wooden spring, k, which can be screwed nearer to the
frame at 1, increasing the force of the stroke. m, is the dis-
tributing board. The orey matter is conveyed on the por
tions, m', m', which, if the table is five feet wide, for the pur-
pose of purer separation, cannot be made wider than twelve
inches. Over the balance of the distributing board, m", m",
the clear water is distributed so as to spread it as uniformly
as possible over three-fourths of the table width (of four feet
width). The clear water is first led into the box, o, and from
there through cocks or some other arrangement to the distrib-
uting board, m.
The manipulation is as follows: According to the material
to be operated upon, the inclination of the table, the quantity
of clear water, the stroke, and the number of strokes per min-
ute, are regulated. When this is done, the table is put in
motion and the clear water admitted. The well-sized sand is
then conducted on the portion, m', of the distributing board.
The denser ore particles will soon follow the influence of the
percussion and assume the diagonal direction under the clear
water which carries the lighter particles down, so that the
heaviest part will enter the partition, n", the less dense min-
eral slides into n', and the valueless earthy part is carried to
2. In case the stuff in n" should be required more or less
pure, the movable dividing list, p', must be turned to the right
or left side. By this means it is possible to extract the galena
perfectly pure in n", the iron pyrites with a small proportion
of galena in n', and the earthy refuse with an insignificant.
amount of ore in n, if the ore should consist of the above
named constituents. The richest part is carried through r,
into the trough beneath, n", (Fig. 9) the middling stuff falls
through the slit, r', dropping into n', and the refuse into the
trough, n, through the slit, 7".
The stuff from n', of two double tables, is generally lifted by
CONCENTRATION.
185
a bucket-wheel and concentrated again on one of them, so
that of two tables three single partitions work on fresh ore,
and the fourth on the middle stuff of n' of all four partitions.
No intermediate stuff has to be handled, only first-class ore
being obtained in n", while the refuse in n is discharged from
the works as valueless.
The inclination of the table increases with the grain size,
and is-
For sands...
в
slimes..
..6 degrees.
3
The quantity of stuff conveyed to the table per minute
ought not to be more than-
Of sands-0.22 cubic feet, containing, per cubic foot of dry
stuff, 17 pounds on one distributer.
Of slimes-0.11 cubic feet, containing, per cubic foot of dry
stuff, 6.8 pounds on one distributer.
Consequently one double table will put through in twenty-
four hours--
Of sands.
"slimes..
..5.38 tons.
1.08
Or an average as the stuff comes from the battery from
three to four tons (of two thousand pounds).
Of clear water, the table requires per foot width about as
much as comes over the distributor per minute-that is:
For sands.
(C
slimes.
.0.22 cubic feet.
.0.13
(*
Or for a whole compartment of the table per minute-
For sands.
((
slimes.
•
•
10.66 cubic feet.
0.39
The quantity of clear water must increase in proportion as
the inclination of the table decreases. It is also necessary to
direct more water on the outer edge of the table than towards
the stuff, in order to carry off the schlich.
The number of strokes-
With sands is...
slimes
13
70 to 80 per minute.
.90 " 100
(.
186
CONCENTRATION.
With tough slimes, the strokes may be increased to 120 or
140 per minute.
The length of the stroke is dependent upon the tension of
the spring, k, by which the table is constantly pressed
towards the percussion block. The spring is about eleven
feet long, three inches wide, and two and a half inches thick.
If the spring receives a tension of from one hundred and
eighty to two hundred pounds, the stroke must be-
For sands...
แ
slimes.
•
2 inches.
3
((
2
If the tension* were too strong, the grains would assume a
reverse course. The tension must be weaker, and the inclin-
ation less, if there is less sand in the dilution than seventeen
pounds.
On four continual double percussion tables, from ten to fifteen
and a half tons can be subjected to concentration in twenty-
four hours, if the stuff is conveyed through four pointed
boxes from the battery, and the four classes obtained concen-
trated separately on one table. The middle produced, how-
ever, must be conveyed to other tables. Of sands free of
slime, a greater quantity can be worked on the above four
tables.
The loss is, like that on other first-class concentrators, about
twenty per cent.
Free Gold, if present, separates perfectly from other ore
and sulphurets.
One table requires a quarter of a horse-power. The con-
centrating expenses are greatly reduced by the self-discharg-
ing percussion tables. At Rodnau (in Hungary) seventy
hands were employed at the concentration works, using sweep-
*The simplest way of measuring the tension of the spring is to tie a cord to the
end of it, where the power is transmitted to the table, and to fasten to the other
end of the cord, which hangs over a roller, so much weight that the spring is
brought out of its position perceptibly. This method is sufficiently reliable for
such purposes; but, as a matter of course, the weight of the hanging part of the
cord, as well as fifteen per cent. of the whole weight for roller friction, must be
subtracted from the tension weight.
CONCENTRATION.
187
ing tables. This number of hands was reduced to eight, on
the same quantity of ore, worked by the continual percussion
tables.
The elevating wheels are seven and a half feet in diameter,
with forty-eight buckets on each side, made of sheet iron.
The inclination of the buckets towards the radius of the
wheel is sixty degrees. It makes four revolutions per min-
ute. The width of the bucket partition on one side of the
wheel is three inches, sufficient to lift the middle-class of one
double table. It is better to use one elevating wheel for sev-
eral tables.
In building Rittinger's table, the frame is put together as
shown in Fig. 12, Tab. V. h, is the percussion rod, on which
five cross pieces are fitted and bolted, and finished to a rec-
tangular frame by the transverse pieces, c, c.
The floor, a, to
be laid on the frame, is generally made of maple wood one
and a quarter inch boards, free from knots. The boards are
fastened to the frame with wooden pins and smoothly planed.
Carpenters, especially in California, are in the habit of put-
ting their tools while working on the already planed floor,
which should by no means be tolerated, although to an inex-
perienced person it would seem a pedantic measure. Dam-
ages of that kind, insignificant as they may appear, are injur-
ious in the process of concentration. When planed and fin-
ished with sandpaper, the partitions and sides, e, are fastened
and closed at the head with a list, f.
In order to effect a strict separation, the point of the divi-
ders, p, p', (Fig. 8) must always touch the floor. These
tongues, however, if not properly made, never make tight
dividers. A very suitable mode is shown in Fig. 10, Tab. V.
The movable tongue, p, has a step on the lower end, form-
ing a dove-tail, gliding, if turned, on the fixed part, e. Above
the tongue there is an iron rod, f, screwed on at the centre of
motion, g. The rod on its upper end has a set-screw, h. By
means of these two screws, g and h, the tongue, which is lined
with leather on the under side, can be tightened at pleasure.
188
CONCENTRATION.
C. Hunter's Self-Discharging Percussion Table.—This con-
centrator, introduced in several mills in California, is made of
copper plates, in an oblong shape, the shorter side being about
twenty-four inches, the longer thirty inches. The table is
somewhat deeper in the middle, (one-half inch) ascending in a
straight line towards both ends, both of which discharge con-
tinuously at the rate of the feeding. At the head, which is
placed a little higher than the level of the opposite side, the
denser ore particles are discharged, while the light waste is
thrown off in the opposite direction. The suspended table,
whose inclination can be regulated easily, receives two hun-
dred and twenty-five strokes per minute. This speed and the
peculiar motion has the effect that the percussion must be
applied on the discharge side of the tailings, the denser par-
ticles taking the reverse direction. Clear water is conducted.
and distributed nearer to the head, the sand towards the mid-
dle of the table. The copper in the middle of the table is
amalgamated for the purpose of catching gold, amalgam and
quicksilver, if present in the stuff.
The efficiency of these tables is more than proportionate to
the size, which is rather small. The general fault in treating
these tables is overcharging with unsized ore. The laws of
gravity and the conditions of concentration cannot be violated
by overcharging without a severe loss being the result. This
may often be the cause of bringing a really good machine
into discredit.
Hunter's percussion table separates, if properly treated,
very satisfactorily, and may work through from two to two
and a half tons in twenty-four hours, according to fineness of
sands.
The amalgamated plate is injurious to steady concentration.
This and amalgamation are two such different operations that
the first is always injured by amalgamating arrangements, no
matter what they may consist of. It might safely he conjec-
tured that, if the amalgamation really does not interfere with
the concentration, the machine must be a second-rate concen-
trator. If the ore particles have to slide on a plane for the
CONCENTRATION.
189
purpose of being separated from gangue, a smooth surface, to
a certain degree, is a condition. A rough surface, such as is
formed by a gathering of amalgam, is a great impediment to
the motion of grains, and it is still worse if quicksilver is
taken up from such stuff which may contain it, by which a
new underlayer for the ore is created, moving its own way.
The periodical removal of the deposited amalgam is no rem-
edy. The amalgamation is no additional recommendation for
a concentrator. Finally, there rises the question, to what
purpose is the catching of gold, which is never perfect on a
concentrator, by means of quicksilver, separately from the
other concentrated portion containing gold and silver? If,
however, a separation of free gold from sulphurets should be
required, it must be done by the concentrator based on the
difference of specific gravity, either in the first operation or
for itself, after concentration, but it is wrong to molest the
concentrator with trifles which weaken its efficiency.
Hunter's concentrator was improved lately by the addition
of rotary discharging plates.
D. Percussion Buddle.-Varney's self-discharging percus-
sions buddle is the only percussion table of a circular form,
similar to the rotating buddle ($48, B). The efficiency of this
table did not meet the expectation, although the construction.
is founded on a right principle. The reason of its non-success
lies in the small size and partly in the application.
The table was built four and a half feet in diameter. The
concussion decreases towards the centre, so that only about
one and a half feet active length of a table partition was left
for the separation, without any provision for obtaining clean
sulphurets. In fact, the periphery of a circle five or six feet
in diameter, ought to be the beginning but not the end of
separation, consequently not less than fourteen to sixteen feet
diameter ought to be considered the proper size of a percus-
sion buddle.
Dividing the buddle into twelve segments (Fig. 12, Tab.
VI,) each will represent a self-discharging percussion table of
190
CONCENTRATION.
five and a half feet length, and four feet width, on the outer
periphery. It is not necessary to give to the table at the
head the same width as at the discharge, for the reason that
the ore requires only eight inches flowing down from the dis-
tributers, b, b. It spreads gradually as the table widens. For
coarse sand the stroke on the, outer periphery may require
to be four to five inches. This stroke would gradually
decrease to about two and a half inches at the head of the table.
By the percussion the denser particles, e, will take a diag-
onal course in the same way as on the continual percussion
table, and come out of the stream. For this reason, and to
carry off particles of sand, there is a perforated pipe, c, for
each table, receiving the clear water from the circular pipe,
g. The circular main distributer, d, provides the distribu-
ters, b, b, with sands.
Compared with the continual percussion table, this buddle
of sixteen feet diameter and twelve segments ought to sepa-
rate about twenty tons of ore in twenty-four hours, consum-
ing about seven cubic feet of clear water for coarse sand, or
4.5 cubic feet for fine sand and slime per minute. On the
same buddle, two or three sorts of sand can be operated upon
at the same time, giving less clear water for the finer sort on
separate compartments.
A good result of the percussion buddle depends on-
1. The right proportion of sands, water, and inclination.
(six degrees).
2. On a perfectly level and smooth floor of each segment-
the segments being divided by rims, h, of a triangled section,
one or one and a half inches high.
3. On a steady forward and back motion of the periphery.
This could be easily accomplished by a proper support of
rollers, or wheels, on four points equi-distant.
4. On the uniform distribution of the percussive power
on each segment. The percussion beam must be the length
of the diameter of the buddle, in one piece through the cen-
tre, and both ends striking at the same moment against hori-
zontal or vertical percussion blocks. All twelve radial arms,
CONCENTRATION.
191
including the percussion beam, must be connected on the
periphery by cross-pieces.
5. The tension of the spring must be adjustable.
Except the decrease of the percussion towards the centre
of motion, the single segments resemble completely the con-
tinual percussion table. The buddle might answer better if
only one-half of the circle should be fixed to the shaft. This
would allow a better division in regard to room, and simplify
the application of the percussion and motive arrangement.
SEC. 47.
Oscillating and Shaking Tables.
These tables answer for sands better than for very fine
material. They are not much in use, because they do not
give a clean separation, and lose, at the same time, more
metal than others in use. But they have the advantage of
being simple and inexpensive, requiring very little power
and not much room. They are suitable for concentration of
tailings, etc., where concentration is a secondary matter.
The best concentrators of this kind are the following:
A. Borlase's Concentrator is represented on Tab. IV. Fig.
6, is a perpendicular section. Fig. 7, shows the view from
above. The ore is conducted through a trough into an annu-
lar vessel, a, whence it flows over the rim on the distributor,
b, which is inclined, stationary or revolving. Through the
holes, d, the ore drops on the level bottom of the oscillating
pan, e, which is kept in motion by the cranks, g, g, and the
rods, h. By the quick motion, the orey stuff is kept in a
loose condition, so that the heavier part can descend and
deposit itself at the bottom, whilst the lighter stuff is carried
by the water through the central opening, i, over the inner
ring, which is movable, and raised mechanically in proportion
as the deposited ore rises on the bottom. This apparatus is
192
CONCENTRATION.
provided with a revolving cylindrical sieve and percussive
hammers, for settling the ore if required; also with an appa-
ratus to increase or decrease the speed, which is omitted in
the drawing.
rets.
B. Hendy's Concentrator.-This concentrator is an im-
proved modification of the former, and is used extensively in
California on tailings, principally to concentrate the sulphu-
The improvement consists chiefly in the bottom slightly
ascending towards the centre; in the application of a dis-
charge hole on the side close to the bottom, provided with a
gate, so that by opening it somewhat a continual discharge of
the concentrated stuff can be produced; and also in connect-
ing the upper box of the upright shaft with a crank handle.
By this means an inclination can be given to the discharge
side. The refuse is carried through the centre, as in Bor-
lase's machine.
The gate at the discharge hole must be shut at the com-
mencement until the sulphurets accummulate above the
opening. The gate is then opened very little, so that only a
small quantity may come out continually. If it is perceived
that the sulphurets rise in the pan, the gate may be opened
little more until the discharge is equal to the quantity of
sulphurets constantly deposited.
Much would be gained on the percentage of concentrated
sulphurets if the ore or tailings were conducted through two
small pointed boxes, ($43, D,) of different sizes, and two or
three concentrators used for each sized stuff. The motion of
the concentrators must be modified-the first concentrator,
receiving the coarsest grain, must have the longest stroke,
and probably more water; the last one, working upon the
finest sand, must move quicker, with shorter strokes. The
crank shaft makes from one hundred and eighty to two hun-
dred revolutions.
C. Hungerford's Concentrator.-Similar to the preceding
is Hungerford's machine. The bottom, as shown in Fig. 8,
CONCENTRATION.
193
Tab. IV, ascends to the rim of the sufficiently-inclined chan-
nel; a, which, at the lowest point, discharges the refuse.
There is a circular trough, b, outside the periphery. At
intervals of a few inches around the circumference, there are
small openings at the bottom, by which the inner space com-
municates with the trough. The pan derives its motion from
two eccentrics, secured on a horizontal shaft, passing across
and below the centre of the pan, and working between two
pairs of adjustable wooden guide-blocks, or bearings. The
eccentrics are so made as to bear equally on the wooden
guide-blocks in all positions while in motion.
The pulverized material flows from the feeder, c, into the
bowl, distributing thence equally over the convex cover, drop-
ping into the pan. By the motion of the pan, the heavier
particles are kept near the periphery, passing through the
openings into the trough, from whence they are removed as
fast as it is filled. The light gangue is carried by the flow
of the water through the channel, a. The construction of
this concentrator is very simple, and not liable to get out of
order soon.
D. Shaking Tables are very imperfect concentrators. The
main feature is explained by a box eight to ten feet long and
twelve to fifteen inches wide, more or less, having a smooth
or riffled bottom. It is suspended on four rods, and receives
its motion by a crank. To this class belongs—
E. Barron's Concentrator-Which differs in construction
entirely from the common shaking table, giving also, with
proper material, a better result. A half-round trough, from
six to eight inches wide and six feet long, is suspended on
four wires. An iron rod imparts to the trough a rocking
motion. Another motion forwards and backwards is effected
by a crank. The trough is suspended in an iron vessel of
about fifteen inches in width and ten feet long, filled with
water, so that the trough operates under water. The ore is
fed through the hopper into the somewhat inclined trough.
194
CONCENTRATION.
The quick motion keeps the sand loose, so that the heavier
grains sink to the bottom, whilst the gangue floats on the top,
all moving downward in the inclined trough, but the rocking
motion brings the stuff alternately nearer to the rim, below
which, on both sides, are made longitudinal openings, through
which the light refuse is thrown off into the larger com-
partment of the vessel, while the concentrated part is con-
stantly discharged in the front compartment. The trough is
about six inches wide; the machine nevertheless is capable
of doing a great deal of work, separating from ten to twelve
tons in twenty-four hours, (of coarse galena ore).
The advantage of this concentrator is the small quantity of
water necessary for the operation, which is of importance in
some localities. A good result, however, cannot be obtained
in treating fine sand or tailings, and it is also a condition, as
in all other machines, that the ore should be sorted before it
is led into the hopper.
SEC. 48.
Steady-Moving Concentrators.
These concentrators are suitable for concentration of sands
not over one-forty-eighth of an inch diameter, but superior
for fine material and slimes. The most important are the
rotating buddles, which are derived from the stationary bud-
dle. The rotating tables concentrate a great deal more per-
fectly than the stationary do. There is no accumulation of
concentrated stuff on them, which creates a change of the
inclination, as is the case on the stationary round buddle, no
stoppage on account of removing deposits, and the power
required for one rotating buddle is insignificant. The first
rotating table was tried in the Harz, in 1853. The stuff to be
concentrated is conducted over a stationary distributer upon
an inclined plane, which has a slow circular motion. By this
motion the ore is constantly carried from under the distribu-
ter to a flow of clear water, sufficient to wash down the light
CONCENTRATION.
195
earthy particles, while the denser part remains on the table
or moves down slower than the refuse. In course of the
motion the heavy deposit arrives under a jet of water, by
which it is removed in a separate trough. There are two
kinds of rotary buddles-1st, Rittinger's concave, and 2d, the
convex German buddle. Both have an inclination of from six
to seven degrees. This inclination may serve for different
classes of sand, only the quantity of water must be regulated
accordingly. Both kinds of buddles give very satisfactory
results. To obtain this, a uniform feeding with a uniformly
diluted ore, a uniform motion of the buddle, a steady flow of
clear water, and an equal division of the compartments, are
necessary conditions.
As to the washing planes of the buddle it may be noticed
that they are not conical, but consist generally of sixteen
pyramidal planes, inclined to an angle of six degrees, either
towards the centre (concave) or from it (convex). Each of
these sixteen divisions is again divided by narrow lists into
two halves. They require to be smoothly planed, and not
damaged by careless putting of tools upon the finished sur-
face, as is the habit of almost all carpenters. The boards
must be fresh from the saw-mill, or if dry, they ought to be
kept under water for twenty-four or forty-eight hours.
A. Concave Rotary Buddle.-This concentrator (Ritting-
er's) is in very successful operation in Hungary, Bohemia,
etc. The construction of this concentrator is represented in
Tab. V. Fig. 1 shows the central vertical section of the
ground plan, Fig. 2. The vertical shaft receives its motion
at b, from an endless screw which is not shown in the draw-
ing. On this shaft, by means of a key, is fastened an iron
flange, c, for the reception of sixteen wooden arms, composing
the frame of the table on which the floor, e, is laid. It has
sixteen pyramidal planes with the greater base at the peri-
phery. The joints of the flooring on the middle of each arm
are covered with a three-sided list with the edge upwards,
about three-quarters of an inch high. Each of these planes
196
CONCENTRATION.
is divided into two equal parts by lists, f, of the same descrip-
tion, so that the table surface consists of thirty-two equal
compartments, ending towards the centre in small funnels, n,
Fig. 4, (shown on a larger scale). These funnels, however,
are not absolutely necessary. No iron nails are allowed to be
on the concentrating surface, only wooden pins. The ore is
conveyed upon the buddle over the distributors, g, g. These
are kept in position by iron holders, z, Fig. 4, A, fastened to
the trough, l. There are eight distributers on the periphery
of the buddle, sometimes only four. Six of the distributers,
g, g, receive the ore from the trough, h, the remaining two,
g, g', bring the middlings of the concentration back on the
buddle.
The circular water-trough, l, supplies the buddle with clear
water on the periphery after each ore-distributer. For this
purpose a separate small trough is formed by a piece of sheet
iron or zinc, k, as seen in Fig. 3. For a better distribution
of the water, the zinc is prepared with teeth on both of its
long sides and nailed to the projecting bottom, a, so that
about three and a half inches of the zinc project below the
trough and two inches above the bottom. The trough is
three feet six inches long and receives its water through a
cock from the trough, l. Near this water-distributer, k, there
is the cleaner, m, shown on a larger scale in Fig. 5. The inch
pipe, m, provides the buddle with a jet of water under a pres-
sure of six to eight feet, by which the deposited schlich (the
concentrated stuff) is washed off. The end of the pipe, m',
is a lead piece with a narrow flat opening.
Below the buddle is the stationary reception trough, o, dis-
charging the different educts into r, p, q, whence they are
conveyed further. Fig. 6 explains the construction. It con-
sists first of the circular lower trough divided in three circu-
lar compartments, p, q, r, each having one or two discharge
holes, e', é", above launders, s, ', s'. On this circular trough
is another one, o, with radial divisions, a, b, c, forming sepa-
rate inclined troughs of unequal width, leading the stuff
through openings on the bottom into the respective lower cir-
cular compartments, p, q, ".
CONCENTRATION.
197
The reception trough is so arranged that the compartment,
a, corresponds with the ore-distributer, g, of the buddle, so
that while the segments, receiving the ore from g, move slowly
under the clear water of k, the tails being washed down, enter
through the little funnel, n, of the table, into the radial trough,
a, which is shot off towards the centre, and the tailings are
led to find the way through the hole at the bottom into the
trough, p, and from there through e', into the gutter, s. The
middles are discharged in the same way into the radial, b,
then into the circular launder, q, and from thence through s',
to the elevating wheel, u. The schlich is carried by the jet
of water from m, through the gutters, c, r and ', into a sep-
arate box.
It is clear that, if it is desired to obtain less middles or none
at all, a, must be wider than b, or the partition between the
two is entirely omitted. c, may be wider or narrower, accord-
ing as poorer or richer schlich is desired, keeping only the
distance from the first partition of a, to the last of e, unaltered.
In case there are six, four or one cleaner, m, the compartment
of a, will occur six times, four times, or only once in the whole
circle correspondingly.
The reception-trough could be more simply arranged if
only the circular part, p, q, r, were fixed below the buddle,
sufficiently inclined and the funnel, n, directed to discharge
into the middle compartment, q; if these movable boxes were
placed on the middle trough, one box opening towards the
periphery, the other box towards the centre, as shown by
dotted lines, Fig. 6, the discharge of the relative sorts would
flow into p and r, when the funnel, n, passes over it. Similar
movable boxes are in use above o, Fig. 1, to regulate the dis-
charge into a, b or c, open on one side of the circular line.
The concentrating process is now easily comprehended.
The sand or slime to be concentrated, falls from the distribu-
ters, g, on the slowly rotating buddle, (six revolutions per
hour) being thus carried under the clear water of k, to which
it is exposed for about three-quarters of a minute while mov-
ing. By this time (after one segment, for instance, has passed
198
CONCENTRATION.
first the compartment, a, of the receiver, o, discharging into
it the tailings, then the compartment, b, which received the
middle stuff) only the denser part of the ore remains on the
segment, which is brought now under the jet of the cleaner,
m, and washed down into c, of the receiver. The washed seg-
ment moving on, passes the next distributer in the same way,
and so on. The middlings from s', Fig. 1, being lifted by the
elevating wheel, u, pass through the funnel box, v, and the
conduit, i, on the distributers, g', g'. The surplus water flows
off through w.
Other tables of this kind have only three to four distribut-
ing boards. It is, moreover, not necessary to wash off the
schlich after each distributer. The first thin stratum of
schlich which is deposited and washed clean by the water
from k, can pass under the second distributer and under the
third, thus producing a thicker layer before it is brought
under the jet. But arranging concentration in this way, less
sand and less clear water must be used; consequently less
stuff can be put through in a certain time.
The inclination varies, according to the material treated,
from six to nine degrees for slimes or sands.
The quantity of stuff conveyed over one distributing board
of eight to twelve inches width is, 0.35 cubic feet of sand,
or 0.15 cubic feet of slime, per minute. The narrower is the
distributor, the easier it is to obtain pure sulphurets after the
first washing.
The quantity of dry stuff in the dilution per cubic foot is-
For sands..
slimes.
10 pounds.
5
The loss is from twenty to twenty-five per cent. One
horse-power is sufficient to run ten to fifteen of these bud-
dles. The table consumes-
On sands..
"slimes....
15 cubic feet of water per minute.
8
((
(
66
And is able to put through—
Of sands...
(C
slimes..
(
((
.6 to 8 tons per 24 hours.
2.8 3.6
CONCENTRATION.
199
B. Convex Rotary Buddle (German Buddle).—The differ-
ence between this and the preceding buddle is in the inclina-
tion. The German buddle is inclined towards the periphery;
consequently the feeding is at the centre. Comparing the
effect of this buddle with the stationary, the following result
will show the difference:
"A lot of slime ore, weighing 61,910 pounds, was divided
into two equal portions. The rotating buddle finished its
portion, including re-washing the tailings, in eighty-six hours,
whilst the ordinary buddle required six hundred and nine
hours to perform the same work. The time consumed was,
therefore, in the proportion of one to seven. The ore oper-
ated upon contained about eight per cent. of lead. The
rotating buddle cleaned its portion of slime ore to 62.4 per
cent., and left only one-eighth per cent. in the waste. The
ordinary buddle cleaned its ore to 52.6 per cent., and left two
per cent. in the waste."*
In the Harz, a pair of rotating tables always work together.
The middles of the first table, which is eighteen feet in diam-
eter, are conveyed on the second table, sixteen feet diameter.
The inclination is five degrees for both tables. If the nature
or size of the ore should require more than five degrees, this
may be managed by giving more water on the table. One
revolution takes two and a half to five minutes. If the
gangue is light, the table can revolve faster. The speed
may be also increased with the richness or fineness of the
stuff. On the rotating table is only one charge for the whole
revolution, (unlike the concave buddle). The clear water
given at the head does not increase, as is the case on the con-
cave buddle, but, on the contrary, it must spread on an
increasing surface. It is therefore necessary to supply more
*Records of Mining and Metallurgy," Phillips & Darlington. According to
A. Lesoine, the above comparison was made on a rotating buddle with 309.55
pounds, and on three ordinary sweeping tables together with 309.55 pounds. The
buddle was attended by one, the sweeping tables by three workmen. The rotating
table performed its work in eighty-six, the three sweeping tables in six hundred
and nine hours.
200
CONCENTRATION.
water, through perforated zinc pipes. Also moving brushes
are applied, in order to renew the washing surface. The
number of brushes depends on the gangue, blende, etc. One
buddle requires, on an average, about four cubic feet of
water per minute.
Rotating buddles of six to ten feet diameter are made also
of cast-iron in one piece. These buddles are sometimes so
arranged that two of them are attached to one perpendicular
shaft. The upper concave is smaller. The middles flow on
the convex larger buddle beneath the concave one. The
construction of convex buddles is very similar to that of the
concave, the principal difference being the convex shape.
C. Brunton's Table.-This machine consists of a table about
ten feet long and four feet wide. On both ends are rollers.
An endless cloth revolves by means of the rollers over the
table. The cloth is stiffened in its width by numerous wooden
laths. The stuff flows over a distributing board on the cloth,
which revolves against the stream. Clear water is introduced
behind the entrance of the stuff. The inclination can be
changed easily. The heavier particles lodged on the cloth
are caught in a wagon beneath, whilst the lighter matter is
floated over the front roller.
The cloth travels about six and a half feet per minute. The
speed, however, must be varied with the condition of the
stuff. This apparatus is extensively employed at Devon,
Great Consols. These tables were used also in California,
but were not satisfactory.
D. Self-Discharging Blankets.-There are several patent
revolving blanket tables, following in construction a wrong
principle of an inclined motion, carrying the deposited denser
stuff directly against the stream of diluted stuff and clear
water, and under the very disturbing fall of sand from the
distributer. It is for this reason impossible to convey the
fine stuff already deposited through the continual charge,
without stirring it all up, whereby the most of it is carried
CONCENTRATION.
201
off again. Besides this unavoidable inconvenience, the sand
which is splashed upward by each drop from the distributer,
is carried up by the blanket, unless there is clear water com-
ing from behind the distributer, which is not practicable on a
blanket, for the reason that the sand must be itself sufficiently
diluted, if intended for blanket concentration. This dilution,
by additional clear water, becomes injuriously increased.
There is only one proper construction of self-discharging
blankets, and this is the principle of rotating buddles. But
as the discharge of the deposit cannot be effected by a jet of
water from a blanket surface, and, on the other hand, it is
impossible to bring the blanket under water with a circular
motion, this last must be changed into a horizontal one.
this principle the author constructed the
On
E. Horizontal Moving Blanket Table in a simple and prac-
tical way. The length, that is, the distance over which the
stuff has to flow, is only four feet, but it will be seen that,
according to the speed given, the length can be indirectly
increased to such an extent that the stuff never would reach
the end of the four foot wide blanket. Figs. 16 and 17, Tab.
IV, explain the arrangement. Fig. 17 is a central cross-sec-
tion of the front view of Fig. 16. The rectangular frame, a,
eight feet by four feet four inches in the clear, contains two
shafts, b, (only one represented in the drawing) each of them
furnished with two chain-wheels, c, c'.
The support of the blankets is formed by a number of laths,
each one and a half inches wide, five-eighths of an inch thick,
and four feet long. There is half an inch space left between
them. Corresponding with the distance and position of the
chain-wheels, there are india-rubber belts or strips, e, e, two
inches wide, screwed to each lath. On the rubber are fastened
the chains, d, d, by means of copper-wire, between the laths
from six to eight inches distance. This arrangement of laths,
about fourteen and a half feet long, is placed over the wheels,
as seen in Fig. 16, and the ends joined to an endless lath-table.
In order to obtain a level surface of the blanket, the chains
14
202
CONCENTRATION.
must move on guide boards, f,f, which are fastened to the
arms, g, of the cross-piece, g', of the frame. By means of slits,
h, the guide boards can be adjusted to the proper line. The
top of the guide board is shown in Fig. 18, Tab. IV, on a
larger scale. One of the shafts at the elevated end connects
with a cog-wheel and endless screw, by which the motion is
imparted to the table (not shown in the diagram). The
boxes, g', of the other shaft have some play for adjustment.
The blanket is prepared on the underside with a mixture of
asphaltum and India-rubber, or rubber alone, in order to
make it water-tight and somewhat stiff, but not too heavy.
The blankets, n, are used in three or four pieces. One end is
screwed to one of the laths, as shown by the dotted line, i.
This end must be covered by the preceding for about six
inches. The covering end is loose, provided with a lath, the
ends of which have iron hooks, l, l (Fig. 17). On the inside of
the endless laths, there are strips of zinc, m, screwed to a lath.
The hook rests on m, when the blanket is below. Moving
over the wheels the blanket is exposed to stretching, and
quiet motion could not be effected if both ends were fixed.
The hook slides on the zinc, m, and prevents the stretching
of the blanket which hangs free two or three inches below the
lath, n'. In order to prevent the sliding of the hook from the
zinc, there are two pins, p, one on each side of a lath.
The whole apparatus rests in a water tank, indicated by
dotted lines, q. The water level is shown by x. The blan-
ket revolves about eight feet per minute, but the speed must
be regulated according to the degree of intended concentra-
tion. The front part is lowered as much as nine or ten
degrees from the horizontal line. This inclination must be
accommodated to the quantity of water and stuff. The length
of the table from shaft to shaft is six feet, sufficient for two
five-stamp batteries. There are two distributers, t, t, one for
each battery. On account of the motion of the table, the
sand takes the course as indicated by v. This transverse
direction increases with the speed of the blanket. By this
means, the quantity of concentrated stuff from one ton of ore
CONCENTRATION.
203
is easily controlled. There is a pipe, u, Fig. 16, with small
holes below, conveying clear water on the blanket for the pur-
pose of washing off the gangue. A trough in front removes
the tailings (the trough not represented).
Owing to the nature of the blanket which offers for concen-
tration a very rough surface, a clean educt, for instance, pure
sulphurets, cannot be obtained. This, however, with free
gold and rich sulphurets, is not necessary, and for this reason
the blanket is, of all concentrators, the most independent of
sizing.
Using canvas or duck No. 5-0, twenty-two inches wide,
and forty feet long, in place of the blanket, the table produces
a clean stuff and proves to be an excellent contrivance for
saving gold, fine sulphurets and quicksilver scum.
But a
table of forty feet length, that is, from shaft to shaft, concen-
trating, only on the upper part, cannot work more than
from five to six tons crushed stuff in twenty-four hours. When
the duck passes down over the drum, the concentration can
be performed on the inner side in the same way as above the
drums, but the result is less favorable, probably for the rea-
son that the duck acquires a smooth surface in passing over
the roller, particularly between the laths. Employing duck,
the arrangement must be changed in several points:
1st. At the length of forty feet (or less) with two or more
continual feedings and as many discharges of concentrated
stuff by water jets as applied on the rotating buddles, the
chains and chain-wheels must be replaced by iron drums of
eighteen inches diameter, twenty-four inches long. 2d. The
laths are fixed differently, only twenty inches apart, screwed
directly on the duck from both sides, as shown in Fig. 20,
Tab. IV, so that not the duck, but the laths, slide on the guide
boards, f. The laths are five-eighths by five-sixteenth of an
inch and twenty-two inches long. 3d. One drum must be
movable, with a play of from eight to ten inches, arranged
with sliding boxes and screws, in order to strain the duck
before the start and to slacken it after it is thoroughly wet-
ted. The duck is in one piece. The laths have little copper
204
CONCENTRATION.
hooks on the upper end, which fall into an iron or zinc guide,
a, Fig. 19, Tab. IV, which extends the whole length of the
table above and below. There is no water-tank required, as
the concentrated stuff is washed off by water jets.
+
IV. SPECIAL CONCENTRATION.
SEC. 49.
Concentration of Gold Ores.
A. The concentration or separation of gold from crushed
ore is performed in three ways-first, by quicksilver; second,
by water on an inclined plane, and third, by amalgamation
and concentration combined.
The gold sinks in quicksilver so much the easier the less
silver it contains and the coarser the particles are; but also
low gold, containing from forty to fifty per cent. of silver,
being then nearly of the density of quicksilver, will separate
from the sand, as the quicksilver adheres to the gold, coating
its surface. The coating is not instantaneous. The sand
containing gold must be stirred for some time in contact with
quicksilver in order to coat it; low gold longer than high-
graded.
The quantity of mercury necessary for separation varies
largely according to the mode adopted. The arastra and bat-
tery amalgamation give a better result if only so much
quicksilver is used as is required to form a hard amalgam.
The pan amalgamation, on the contrary, needs from sixty to
one hundred pounds of quicksilver as a constant charge in
the pan.
Quicksilver always dissolves gold, but fortunately only to a
certain amount-three-fourths to one and one-fourth ounces.
206
SPECIAL CONCENTRATION.
to a hundred pounds of mercury. This dissolved gold is
constantly retained,* unless retorted; but even in this case a
small percentage of gold will be found in the distilled quick-
silver.
1. Treating gold ores in an arastra, quicksilver is added
in proportion to the gold in the quartz (as learned by experi-
ence or by a fire-assay) but not in one charge. After the
rock has been ground tolerably fine, one-half or one ounce,
according to the richness of the ore, is scattered over the
pulp through a piece of cloth or leather, which must be dry,
at intervals of half an hour. The charge is continued until
a sample of the pulp, washed in a horn-spoon, does not show
a particle of free gold. The amalgam accumulates mostly in
the crevices of the stone bottom and on the sides.
2. Using quicksilver in a battery, about the same propor-
tion in reference to the amount of gold in the rock is taken
as in the arastra. Every half hour, or every hour, one-eighth
to one-half of an ounce of quicksilver is introduced at the
feed side into the battery, while crushing is going on. The
gold unites readily with the mercury, and accumulates, as
amalgam, in batches, depositing in the corners of the battery
and along the screen, in and outside, on amalgamated copper-
plates, which are sometimes applied on both long sides inside
the battery. But the amalgam is also found in very incon-
venient places, in the key-holes of the stamp-heads, on the
shoulders of the shoes, etc. For this and other important
reasons, (§42, 1) battery amalgamation cannot be considered as
a proper way of saving gold. If too much quicksilver is
introduced, a part of it is thrown out through the screens,
on the platform, in drops. The amalgam outside the screens
is a guide as to the quantity of quicksilver to be used. If it
is found so soft that it yields easily to a touch with the finger,
the charging of mercury must be stopped for several hours;
but if the amalgam appears too hard and dry, crumbling to
*After eight months of quiet standing, the gold amalgam crystallizes and
deposits on the bottom of the iron jar.
SPECIAL CONCENTRATION.
207
pieces when pressed, a little more quicksilver must be
administered. ·
If, owing to peculiar circumstances, it is preferred to use
quicksilver in the batteries, copper-plates are generally fixed
on the platform, also in troughs ten to twelve inches wide.
The copper is amalgamated.* It takes up some of the escap-
ing amalgam and quicksilver. More effective in troughs in
place of copper sheet is copper wire-net, from three to four
meshes to the running inch; also coated with quicksilver.t
The trough is from six to eight inches wide and six to eight
feet long, the bottom covered closely with copper wire-net,
so that no sand is permitted to flow underneath, but all runs.
freely over it. For this reason the trough must be suffici-
ently inclined (one and a half to two inches per foot). Some
quicksilver should be strained over the head of the copper
wire trough every day, or every other day. The deposited
amalgam is brushed off every week, or every month, as
the case may require.
The worn-out wire, for the purpose of regaining the amal-
gam, is exposed to a red heat until all the copper is oxidized,
and then amalgamated or dissolved in diluted sulphuric acid.
In the last case, the gold remains undissolved.
From the copper arrangement, the sands are conveyed over
blanket troughs, ($45, F) or over revolving blankets ($48, E).
The blanket-sands, if free from auriferous sulphurets, con-
tain only gold, amalgam and quicksilver to be extracted. This
is best performed by amalgamation in common pans, with
addition of a few pounds of quicksilver and dilution with
water, which is kept warm, but not too hot.
*The amalgamation, or the coating of copper-plates with quicksilver, is per-
formed in different ways. A good result is obtained by putting the copper-plates
into a wooden vessel with sufficient water to cover the uppermost plate two or
three inches. Very little sulphuric acid is added to the water, so much as to
make it taste like strong vinegar. After six or twelve hours, the plates are taken
out, washed in the same liquid, and the quicksilver rubbed over the surface before
the plate becomes dry. Washed in cold water, the copper is then prepared for use.
†The copper wire can be treated in the same way as described under *, but must
be fixed to the bottom before being amalgamated. Addition of some sodium
amalgam to the quicksilver covers the copper freely without the acid bath.
208
SPECIAL CONCENTRATION.
In presence of auriferous sulphurets, if not over-charged
with galena, the blanket stuff must be concentrated and after
roasting subjected to the chlorination process, or if this can-
not be done, worked in grinding pans, ($30, E, F,) with the
addition of quicksilver, without roasting and without concen-
tration, for ten or fifteen hours per charge.
Rich gold specimens are pounded up in a hand-mortar, and
the powder triturated with quicksilver and warm water. If
there are no sulphurets present, the use of a small quantity
of sodium amalgam effects a sudden amalgamation.
3. The separation of gold from quartz by means of quick-
silver is further practiced in iron pans, either by stirring
alone or by grinding.
Cl. The amalgamation of gold quartz by stirring without
grinding is extensively applied in Europe, generally in iron
pans (Tyrolean bowls). They are sixteen inches at the bot-
tom in the clear, twenty-four at the top, and six inches high.
The side is broken, forming a step. The outlet is three
inches above the bottom. In the centre is a cone, through
which a perpendicular shaft passes, connected at the top
with a wooden muller, filling up the pan, leaving only three-
fourths of an inch space between the sides and the quicksil-
ver surface on the bottom, (fifty pounds of mercury are
charged in each bowl). These pans are known in California
under the name of "Hungarian bowls," introduced by the
writer in 1854, (Mariposa county). They were adopted in
many mills, but afterwards gave way to grinding pans. In
most cases the result was not satisfactory, although a most per-
fect work is obtained by the same contrivance in Europe. The
reasons were: over-charging, wrong speed and dilution; the
wings projected into the quicksilver, the sand was generally
too coarse, etc.
The mullers are provided with little copper wings, which
are not permitted to touch the quicksilver. The finely-
crushed ore is conveyed through the central opening of the
muller into the lower part of the bowl. The muller receives
twelve revolutions for light ore, and twenty-four for ore con-
SPECIAL CONCENTRATION.
209
taining galena. A larger diameter than sixteen inches does
not answer, as the motion towards the periphery is so much
increased that the gold particles are kept in suspension with
the sand.
Through one bowl, one-half to one cubic foot of diluted
sand is allowed to flow per minute in such a condition that
one hundred pounds of sand may be put through in one hour
containing five, or, at the most, ten per cent. sulphurets. If
there be more than ten per cent. sulphurets in the ore, the
continual charge must be reduced so far that not more than
ten per cent. of sulphurets should pass the bowl per hour.
There are two, sometimes three, bowls, one below the other.
The first bowl retains seventy-four, the second twenty, the
third six per cent. of the obtained gold.
If two rows are arranged so that the lower receives the
sands from the upper bowls, the loss of quicksilver per fifty
tons of ore amounts to-
With heavy sands.
light
1 to 2 pounds.
((
1 1/1/20
(C
In some mills, (Grass Valley and other places in California)
a stirring amalgamation on free gold is performed in half-
round troughs, ($45, F) by which the gold is extracted to
the satisfaction of the superintendents. This apparatus is
simple and inexpensive. The loss in quicksilver will be
very likely considerably higher than the loss by the described
bowls, caused by the pins passing the quicksilver and by the
quick motion.
b. Amalgamation and Grinding is preferred-1, where coarse
crushing is introduced; 2, where light gold appears (alloyed
with forty or fifty per cent. of silver) and, 3, where aurifer-
ous sulphurets occur, provided there is no after concentration.
intended. Coarse crushing on gold ores is improper. This
metal is generally found finely distributed in the rock, and
must be set free therefrom before amalgamation or concen-
tration. The coarse crushing, therefore, must be finished by
grinding. Light gold is more difficult to save by mere stir-
210
SPECIAL CONCENTRATION.
ring than heavy gold, and a slow grinding in this case is pref-
erable. At from sixty to ninety revolutions of heavy
mullers, the amalgamation itself is not defective, although
the gold particles are suspended in the pulp, as the quick
motion prevents the separation by density. It is continually
circulating from the periphery to the centre, forced under
the muller together with the finely-divided quicksilver, so
that contact and amalgamation is very perfect; but it seems
that the amalgam is broken up with fast-revolving mullers,
and therefore more difficult to collect than with common
pans, which are preferred by many millmen for free gold.
The loss of quicksilver with grinding pans is very heavy, and
amounts to from six to nine ounces per ton of ore.
Auriferous sulphurets, when poor, or occurring in small
proportion together with free gold, are best treated in fast-
grinding pans. The extraction of gold from auriferous sul-
phurets by slow-grinding pans is insignificant. Ores with
rich sulphurets and free gold must be excluded from direct
grinding, and treated by the
C.
Combined Method of Concentration and Amalgamation.
This method gives the best result, provided no grinding-
amalgamation is attempted-
1. If the concentrated stuff be designed for smelting on
account of lead and silver, or copper, in which case the gold,
by a preceding amalgamation, is saved from the unavoidable
smelting loss of three to four per cent. and the loss of cọn-
centration.
2. If the concentrated sulphurets be intended for extrac-
tion of gold by chlorination, whereby coarse gold particles
are not converted into chloride of gold.
The loss of gold in concentration is about twelve per cent.
on the average, depending, however, much on the condition
of gold and gangue. This loss consists in the finest and most
unfavorably-shaped particles, of which a portion also escape
amalgamation. Therefore it cannot be supposed that by a
preceding amalgamation all the concentrating loss is obvi-
SPECIAL CONCENTRATION.
211
ated. Considering besides the increased expense in a preced-
ing amalgamation of the whole mass, and the loss of quick-
silver connected with it, a direct concentration-the above
two cases excepted-seems to offer more advantage.
B. To arrange the operation of a mill on gold ores most
profitably, sufficient fall between the outlet of the battery
and the tail-race must be provided. A revolving blanket
requires about fifteen inches fall; each successive blanket
trough of twelve feet length, including the step of connec-
tion with the next trough, about twenty-four inches. The
revolving blanket retains the greatest part of the free gold,
(eighty to eighty-five per cent. of what is obtained by blank-
ets) but a great deal of sand with it. On the speed of the
blanket depends the percentage amount of blanket sand.
What this percentage should amount to can be determined
only by experience in each particular case. If no quicksil-
ver is used in the battery, the stuff from the last blauket, on
examination in a horn-spoon, will show whether some of the
gold escaped the preceding blanket. In presence of quick-
silver, however, the gold cannot be perceived, and its amount
must be ascertained by a fire-assay of the extract.
The revolving blanket and blanket troughs will answer in
most cases where only free gold appears, or with valueless
yellow sulphurets; but if galena, zinc blende, and auriferous
pyrites are present, the troughs must be replaced by concen-
trators.
Whatever concentrator, with exception of blankets, is made
use of, the great advantage of assorted sands for the purpose
of concentration is obvious, and is explained in $42. It is,
therefore, a most necessary measure to conduct the tailings
from the revolving blankets through two pointed boxes,
(§43, D, E) and the assorted sand from each box directly to
the concentrator.
There are doubtless many suitable concentrators not men-
tioned in this book; but it is easy to determine to which of
the described systems, (each system contains one or several of
212
SPECIAL CONCENTRATION.
the best known concentrators) a concentrator in question
belongs. It will generally be a modification of one of those
already described, and a careful examination and compar-
ison, but much better a practical proof, will decide for or
against.
As the free gold is mostly extracted by the revolving
blanket, and there is no silver ore in consideration, the con-
centrator must be able to separate the sulphurets clean with
not over ten or twenty per cent. of sand. But as clean sul-
phurets ought not to be obtained at the expense of a considerable
loss, so, on the other hand, a small amount of sulphurets in
the tailings does not condemn the efficiency of a concen-
trator.
Complicated construction and the efficiency of different
concentrators with reference to power, consumption of water,
room, cost of erection, and pecuniary result, must be consid-
ered and compared. None but continual self-acting con-
centrators should be adopted. Attention must be paid to the
regulation of tables charged with sorted sands. Each sort
requires a change in the inclination of the table or quantity
of water, speed, number of strokes per minute, length of the
stroke, and quantity of the charged stuff per minute. No
table can work different sorts to the same advantage without
observing the modifications dictated by the nature of the
stuff. For gold ores, which are generally crushed fine, two
sorts will answer for concentration.
C. Treatment of the Concentrated Stuff, or Schlich.-The
schlich obtained from gold ores must be divided with refer-
ence to the treatment-1, into stuff without valuable sulphu-
rets, and 2, into such as carry besides free gold, auriferous
pyrites suitable for chlorination, and other sulphurets of
value.
The first class is advantageously subjected to amalgamation
in iron pans (§49, 3, B). As the grinding of quicksilver can
not be prevented, it appears advisable to convey the residue
over a steady-moving concentrator in order to regain the
SPECIAL CONCENTRATION.
213
ground quicksilver and amalgam which escapes the settler or
cleaner.
The second class, containing auriferous pyrites for chlorina-
tion or other sulphurets for smelting, must be treated by such
amalgamators as do not pulverize the sulphurets still finer.
The blanket stuff being always charged with slime and sand,
the sulphurets therein must be separated by concentration
after the free gold has been extracted; therefore no grinding
of these is permitted.
Which of the described methods should be chosen, and to
what extent it should be used, every millman must decide
according to circumstances. A valuable metal like gold will
pay for selecting the best means, although expensive, to make
the extraction perfect; but a small quantity of that valuable
metal renders strict economy necessary.
SEC. 50.
Concentration of Silver Ores.
Not all kinds of silver ores can be concentrated ($2, b).
The concentration of silver ores is generally a most delicate
operation, being subject to heavy loss, which cannot be
avoided. This unavoidable loss, however, can be increased
easily to double the necessary amount by an improper choice
of machinery and treatment. It is, therefore, an important
rule to separate by hand as much of the richer part as possi-
ble, leaving the poorest for concentration, and to reject at the
same time the worthless rock.
Crushing to coarse grains, (§35) such as is required for jig-
ging, will not do with silver ores. They are generally so
disseminated in the gangue that crushing to sand is always
required. Unlike galena, silver ores adhere with tenacity to
the gangue, so that, even if large particles of pure ore should
prevail, a preceding extraction by coarse crushing would not
offer any advantage, inasmuch as the residue could not be
214
SPECIAL CONCENTRATION.
considered worthless; but all of it would need to be reduced
finer for further concentration, increasing the expenses, which
would not be covered by the gain of the double extraction.
According to Rittinger, the average loss at large of poor
argentiferous ores in concentration is:
With coarse sand...
((
middle-fine sand..
slimes...
..40 per cent.
t
.35
.60 to 70
в
(
Although the middle-fine crushing suffers the least loss in
concentration, there is in most cases more advantage in decid-
ing for coarse sands, for the reason that less slime is produced
in this case, and the slime is the portion which suffers the heav-
iest loss in concentration. The reason why the coarse sand
loses more than the next finer, is found in the fact that ore
particles involved in larger sand-grains, are carried off by the
water, while they would remain on the table if freed from
gangue by finer reduction, but, as before mentioned, while
this reduction is going on, other particles already freed are
reduced to slime, and the loss increased.
Concentration Works.-The location of a mill should be
selected always as near the mine as possible, in order to reduce.
the hauling expense. It is also important to choose the site
on a hill-side or on elevated ground, and to build the ore-
dumps high enough above the battery floor, so that the ore,
by means of a shoot, may be easily delivered to the batteries.
The shoot is often replaced by inclined grates on which the
ore rolls down. What falls through the grate-bars (two and
a half inches apart) is suitable for direct feeding; the coarser
ore is generally broken by rock-breakers to the required size.
It is equally important to place the batteries from ten to
twelve feet above the concentrating department, otherwise
the battery stuff would, need to be elevated by bucket wheels
or other means, in order to be conveyed into the sorting
apparatus.
The quantity of water must be carefully considered, and
the calculation made as to how much is required as motive
SPECIAL CONCENTRATION.
215
power, or for the engine, and how much for the battery and
the concentrating tables. It is often the case that the water
falls very short in summer; it is then advisable to sink a
shaft where most water could be expected, to the depth of
forty or sixty feet, and if necessary and admissible, to run a
drift across the stratified rock, in order to increase the water
supplying surface. The concentration may be arranged also
with less water, by pumping up that already used after it has
had an opportunity to settle, and using it over again.
The calculation on horse-power and water quantity may be
explained by an example of concentration works, capable of
concentrating forty tons of ore in twenty-four hours. The
stamps should weigh five hundred and fifty pounds, with a
lift of nine inches-three-quarters of a foot, and seventy-five
drops per minute.
The required horse-power for the stamps on the shaft is
obtained as follows:
550X75XX
60
687.5 foot pounds per second for each stamp,
and as it may be assumed that each stamp will crush one and
a half tons in twenty-four hours, the number of stamps for
forty tons would be 8-27, which, for the sake of a better
battery division, may be put down as thirty stamps,
Aud
30X687.5
550
5
37.5 horse-power for the batteries.
On level ground, all the stuff resulting from forty tons-
equal to about fourteen cubic feet per minute-must be lifted
twelve feet high to the sorting boxes, which would require
about 0.6 of a horse-power.
In order to concentrate all the crushed rock, either percus-
sion or steady-moving tables may be introduced. Although
the steady-moving buddles are most suitable for concentration
of slimes, this nevertheless can be performed also by percus-
sion tables, so that it is not necessary to build different kinds
of concentrators in one establishment, unless concentration is
extended also to tailings from grinding pans, provided there
216
SPECIAL CONCENTRATION.
is sufficient clear water at hand, as the rotating tables con-
sume much more water than percussion tables.
The further calculation will be made for the continual per-
cussion table ($64, B).
A double table will put through three tons of crushed stuff
(average) in twenty-four hours, consequently 40-14 tables
are required for the whole amount, re-concentrating at the
same time the middle stuff, amounting to one-third of the
whole mass. Three compartments of two double tables
receive the ore, and the fourth the resulting middle stuff,
which is elevated by a small bucket wheel of six feet diame-
ter. Two double tables, including the bucket-wheel, take
0.62, and all sixteen tables, five-horse power. Sixteen tables,
in place of fourteen, are substituted, partly on account of a
symmetrical grouping, and also because, for a similar reason,
three stamps have been added.
The total horse-power for 44.5 tons (to be concentrated in
twenty-four hours) is then :
For 6 batteries of 5 stamps each. .37.5
"16 continual percussion tables. 5.0
Elevating of all crushed ore, if
required..
Together.
. 0.6
43.1 horse-power.
The quantity of water necessary for the manipulation
appears as follows :
30 stamps, at 0.5 cubic feet...15
16 tables, at 1
In all ……….
เ
..16
.31 cub. ft. per minute.
It is advantageous to have a separate motive power for the
department of concentration. Employing water-power, it is
preferred to divide even the stamp works into two or three
independent buildings, if there is sufficient fall to permit it.
The stamping houses then stand one above the other, each
having its own water wheel. The crushed ore is conveyed
through troughs to the lowest concentrating department.
SPECIAL CONCENTRATION.
217
This stuff, for the purpose of assorting, may be conducted
most advantageously through pointed boxes.
According to $43, D, the first box should be made×14=13
feet wide, as about fourteen cubic feet of battery stuff is dis-
charged every minute. In place of one and two-fifths, may
be put, for-
The first box...
11 feet wide and 6 feet long.
second box.
third
3
9
(6
06
·
6
"12
(C
(C
((
.
fourth
15.
(C
(%
.12
Each of these four boxes may be divided by a partition
through the width (§43, D,), whereby eight sorts of sand are
obtained, each sort distributed on three partitions of two
tables, the fourth being employed for the middle stuff of all
four, after being lifted and conducted through a small pointed
box, in order to get rid of the surplus water.
The position of these four boxes or double boxes depends
on the arrangement of the concentrators, which may be placed
on both sides of the driving shaft, forming four groups of four
tables each. The first box is then placed between the two
tables of the first group, on that side which is nearer to the
battery. Between the other two tables of the same group is
the bucket wheel for the middle stuff. The second box stands
between the tables of the second group, receiving the sand
from the first box, through a trough on the shaft side. The
trough must be sufficiently inclined, at least one and a quar-
ter inches to the foot. The third box is placed between the last
two groups of four and four tables, and the fourth may be
placed at the end of the last group. The trough between the
third and fourth box is inclined 0.7 of an inch to the foot.
The discharge of each pointed box is conveyed to three
tables of one group, or if, as is preferable, each box should be
*The large dimensions of the boxes are necessary, in order to concentrate the
sand to a consistency fit for concentration, and at the same time to enable all par-
ticles passing the boxes to sink, and thus to prevent the escape of slime from the
last box, which loss amounts to only four or six per cent. This part is so fine
that, being unfit for concentration, it deserves no further attention.
15
218
SPECIAL CONCENTRATION.
divided into two compartments, the discharge of each parted
box is distributed on three compartments of two tables, the
fourth working on middle stuff.
The building for concentration works of this description,
besides the stamping department and engine room, must offer
ample room, having in the clear about forty-five feet by one
hundred feet.
The Cost of Concentration.-The expenses connected with
a concentration of, say forty tons per day, using steam as
motive power, vary a great deal, according to salaries, wages,
price of material, etc. The following is an estimation on
Nevada prices:
•
Superintendence, book-keeping, two foremen,
Interest on, say $60,000, at 10 per cent., on 13,000 tons,
Four feeders, at $3.50, two engineers, at $6@8, :
Two firemen, at $3.50,. .
Four men at the percussion tables, at $3.50,
"L
(
i
•
Two
handling the stuff,
One watchman, $4, blacksmith, $5, carpenter, $5,. . . .
Breaking of ore for the batteries,.
Hauling, 50 cts. per ton,.
Wear and tear,..
Four cords of wood, $10,
Assaying, etc.,
•
$25 00
18 44
28 00
7.00
14.00
7 00
14 00
16 00
20 00
10 00
40 00
5 00
$204 44
This, divided by forty tons, shows an expense of $5.08 per
ton of ore. There are mills in California, etc., crushing the
ore on a more economical scale, employing less men and hav-
ing at the same time cheaper materials. If, besides this,
water-power is made use of, the cost may be considerably
reduced.
Concentration of Tailings, resulting from unroasted silver
ores worked in grinding pans, is of great importance, consid-
ering the large quantities which are discharged daily in
Nevada, Montana, Idaho, etc. Two cañons in Nevada alone
carry from six to eight hundred tons of tailings daily into the
SPECIAL CONCENTRATION.
219
Carson river. The importance of this question is demon-
strated by the most primitive and, for such stuff, most defect-
ive means, by blankets, which, several miles in length, are
arranged in troughs over which the tailings float under very
unfavorable conditions with too little and too much water,
depending on the dam operations of the respective mills.
Still, this blanket concentration, hardly saving one-hundredth
part of what is contained in the tailings, proves to be remun-
erative. Although this fact is well known, no attempt has
been made yet to try a systematical concentration, the favor-
able result of which is almost certain.
It is for this purpose not necessary to build expensive
works immediately. A few thousand dollars are sufficient to
obtain a result on which with perfect safety the further pro-
ceedings can be based, without the least apprehension of fail-
ure. Such preliminary investigation must be executed
according to $52.
The pan tailings are not very suitable for concentration,
but this only for the reason that proportionately a great deal
more slime is produced than by stamping; the unsuitableness
refers, therefore, more to the greater loss to which the tail-
ings are subjected on account of the slime. The ground pulp,
however, is not so fine as judged by the looks of it, or test
with the figures. The amount of slime of the most custom
mills may be less than thirty per cent., and if the loss of
metal on that account, with a proper concentration, should rise
to fifty or sixty per cent., the profit would nevertheless be
large, considering that no mining, no crushing, and no haul-
ing expenses are taken into account.
Owing to the heavy expenses connected with the operations
in Nevada, it is not by any means necessary to be very par-
ticular in each part of the concentration. The assorting, by
way of funnel boxes, must be as perfect as possible, but it
may not appear advantageous to re-concentrate the middle
stuff. It may be also admissible to charge the table a little
heavier than usual, so that sixty to seventy tons could be
managed with sixteen tables of the described capacity, but as
220
SPECIAL CONCENTRATION.
a matter of course by this means the per centage loss will
increase.
A steam engine of six-horse power is sufficient to concen-
trate the above quantity of tailings, but a supply of twenty to
twenty-five cubic feet of clear water per minute (which must
not be really clear) is a condition, and if this quantity could
not be procured, some additional power must be provided for
pumping up the water already used, after settling. If there
should be more water at hand, the last four percussion tables
´could be advantageously replaced by two concave rotating
buddles (§48, A,), on account of the valuable slime which is
generally twice as rich as the sand; but this change would
increase twenty cubic feet of water to forty, as one rotary
continual buddle requires twelve cubic feet per minute. On
the other hand, four continual percussion tables consume six
times as much power as the rotary.
The per centage to which the tailings should be reduced
by concentration, depends on circumstances, and can be reg-
ulated accordingly. Before the tailings enter the funnel.
boxes, they should be conveyed through a rotary sieve, in
order to keep out impurities.
SEC. 51.
Concentration of Lead, Copper and other Ores.
The concentration of the above ores does not differ from
that of silver ores, unless the ore is disseminated in coarse
particles. The mode of concentration, by separating first the
coarse ore particles by jigging, is almost exclusively confined
to galena or carbonate of lead. The brittleness of these min-
erals and the toughness of the gangue, cause an easy parting
at the first coarse reducing, which is not the case with other
ore. A great deal of the refuse or scrapings from the jiggers
or rotary concentrators can be disposed of as worthless. It
is different with copper ores, of which all scrapings have to
SPECIAL CONCENTRATION..
221.
be subjected to fine crushing, whereby the expenses increase,
generally more than is gained by excluding the coarse parti-
cles from fine reduction.
But there are circumstances where a profitable use can be
made of jiggers or rotary concentrators, also on copper pyrites,
where, as in California, low grade ores must be turned out in
great quantities, and which, for the purpose of concentration,
could not bear the expenses of fine crushing, but would admit
a cheap coarse reduction, suitable for jigging. The result of
jigging or treating by rotary concentrators (§40, A,) would
produce a concentrated part and refuse to be considered
worthless. The sorting, however, must be performed care-
fully.
Not only coarse crushed ores, but also the smalls from the
mines and those from dry dressing, amounting in some places
to eighty or one hundred tons per day, are subjected to the
jigging concentration.
It is necessary to convey the different sorts obtained by
washing, sizing and picking, to their respective treatments in
the simplest and shortest way. A large hopper, filled from
the outside, brings the smalls into the building near the wash-
ing apparatus. For small quantities (twenty to thirty tons
per day) riddles will answer for washing and sizing. Of
smalls, about seventy-four per cent. are obtained of a size.
(No. 1, §13) which is suitable for picking, and therefore deliv-
ered to the picking table fixed on a place where sufficient.
light facilitates the sorting. The fine stuff from the smalls is
best conveyed into a labyrinth. Of this stuff generally not
more than from four to five per cent. is obtained and concen-
trated on sweeping or percussion tables.
The intermediate sizes are concentrated on jiggers, of which
one, two or more are posted not far from the riddles. A short
distance off are compartments to receive the concentrated
jigging educt and the selected part from the picking tables.
The refuse of picking and jigging is reduced finer, either
by rollers or stamps, sized and concentrated again by jigging.
The refuse of the second operation is sometimes subjected
222
SPECIAL CONCENTRATION.
once more to jigging after crushing, or it is crushed finer and
finished on concentrating tables. For sorting the sands, con-
sidering the small quantity, the labyrinth arrangement is
sufficient.
Larger establishments use trommels ($12) for washing and
sizing, in place of riddles. The latter are sometimes com-
bined with the trommels. The fine stuff from washing may
be elevated eight or ten feet, and with that from the second
crushing conducted through pointed boxes. Tables, boxes,
stamps, etc., must be so situated as to make the handling
most convenient.
SEC. 52.
Value of Ores for Concentration.
To find out whether a given kind of ore is worth concen-
trating, an experiment is the best and most reliable guide.
The reliability, however, depends on two principal points:
First, on the proper execution of extraction on a sufficient
quantity of ore; and second, on the taking of a true average.
A perfectly reliable trial is possible only on a considerable
quantity of ore, say from thirty to forty tons. The larger the
quantity of ore concentrated, the truer will be the result and
the easier it is to come near to the real average. After pul-
verization, the ore must be sifted through at least three sieves,
for the purpose of sorting. This is best performed under
water. In case unsorted ore is concentrated, the loss will
increase from ten to twenty per cent.
Screens No. 4, §21, can be used for crushing. A fine sieve
should be applied only on gold quartz, or in case the ore.
appears very finely disseminated in the gangue. This can be
easily ascertained by pulverizing a small quantity of the
coarsest sand which has been washed off from the sulphurets
and washing again in a horn-spoon or in an extracting pan.
The concentration can be performed on a sweeping table
($45, C,) of twelve feet length by three feet width, prepared so
SPECIAL CONCENTRATION.
223
that the inclination is easily changed as the different sorts
require. For the coarsest stuff ten to twelve degrees, for the
slime five to six. Each of the four sorts must be washed sep-
arately. For a steady, uniform feeding, the stationary feed
box (§44, A,) is very suitable. The table must have a mova-
ble step, as shown by a, in Figs. 1 and 2, Tab. VII. When
the sand from the first charge reaches the end of the table,
and is washed off by means of clear water, the step, a, is
turned, as indicated by the dotted line, and the sulphurets
from b, washed into the trough below. The step is then
brought to its former position, and step d, arranged in the
same way.
The stuff from d, when the whole amount of the
first sort is finished, must be washed over on the same table,
and the educt mixed with that obtained from the step, a.
The distributing board is shown by c.
For each of the succeeding sorts the lower end of the table
must be raised a little, in order to obtain less inclination, pro-
vided the beginning was made with the coarsest sort.
The concentrated part of each sort is well mixed, dried,
weighed, and samples taken for an assay of each sort sepa-
rately.
In case an extensive trial, as described, cannot be performed,
small quantities, from fifty to one hundred and fifty ounces, may
be taken, but as a part of several hundred pounds which repre.
sent as near as possible the average of the ore. The first
portion of two or three hundred pounds must be reduced to
about two and a half inch pieces, well mixed, spread on the
floor, divided into three parts, and one of these taken and
broken to half of the former size. From this one-third is
taken in the same way as before, broken smaller, mixed,
divided into two parts, and so on. From the last portion six
or ten pounds are pulverized, sifted through three different
sieves, and concentrated each separately.
This concentration can be effected with wooden hand
extracting pans, which, however, require a skillful hand. It
is therefore easier to make a small sweeping table of about
one foot width and five feet length, and to wash carefully in
224
SPECIAL CONCENTRATION.
small charges. The distributing board at the head must dis-
tribute the sand uniformly over the whole width. The charge
may be stopped before the sand reaches the end of the table.
and clear water admitted, distributed like the ore. When
the sulphurets appear clear at the head, they are washed off,
as before described.
Results from too small quantities will always fall short by
twenty to thirty per cent. of operations upon a large scale.
After it is demonstrated by the trial what percentage of
sulphurets can be obtained by concentration, the value of the
educt can be calculated on the resulting assay and reduced to
the ton of ore. From the value must be subtracted per ton :
1st. The mining expense, or purchase price.
2d. The hauling expense from the mine to the works.
3d. The crushing and concentrating expense.
4th. The cost of amalgamation or smelting, including the
loss.
5th. The interest on the invested capital and the working
capital, divided by the number of tons annually expected.
The remainder will show what clear profit per ton of con-
centrated stuff, or per ton of ore, can be realized.
The degree of concentration and the concentration itself
depends greatly on local circumstances. There is a limit
beyond which no concentration can take place profitably, for
instance, some kinds of ore may be sold for the same amount
as the concentrator would derive from a higher bid for the
concentrated stuff therefrom, after deducting the concentrat
ing expense. In other remote places, destitute of fuel, it
may be necessary to concentrate as high as possible to reduce
the bulk, on account of transportation.
With ores containing sulphurets in coarse particles and of
such a nature that it would appear advisable to erect jiggers
and tables, the trial must be made on the same principle, that
is, by reducing the sample first to a coarse grain (of Nos. 2
and 3, §13) and jigging each sort on a sieve by hand, the
scrapings being pulverized and washed on a sweeping table,
etc.
:
V. CHLORINATION.
SEC. 53.
Extraction of Gold from Sulphurets, Arseniurets or
Quartz, by Chlorination.
Plattner's extraction of gold, by means of chlorination, is
based upon the property of chlorine gas, to transform metal-
lic gold into soluble chloride of gold. In this condition it
can be dissolved in cold water and precipitated in the metal-
lic state by sulphate of iron, or as sulphide of gold by sulphu-
reted hydrogen gas. The extraction by this process, if well
executed, is very perfect. According to Allain, one-ten-thou-
sandth of gold may thus be extracted from pyrites, after roast-
ing and freeing it from iron, copper, zinc, etc., by sulphuric
acid.
The chlorination process was successfully introduced in
Silesia, Germany, in the year 1851, on auriferous arsenical
residue, which had accumulated for many years. It is also
practised, with various modifications, in Freiberg, Hungary,
Transylvania, etc.
In California there are several establishments, most of them
in Grass Valley,* for treating auriferous iron pyrites by chlo-
*This process was first introduced in Nevada, Cal., by Mr. Deetken, in 1858.
Since that time, several chlorination establishments have been erected, and kept in
successful operation in Grass Valley, on sulphurets which were concentrated, except
those from the Eureka mine. There was a difficulty with these sulphurets in
chlorination, which Mr. Deetken has overcome, after a few experiments, by adopt-
ing a chloridizing roasting.
226
CHLORINATION.
rination. The extraction of gold from some kinds of pyrites.
is very difficult by amalgamation in pans, by which from
thirty to forty per cent. loss must be suffered, even though
sufficient time and attention is given. Treated by chlorine,
the gold of this same kind of pyrites can be extracted to
within ten per cent.
The chlorination process admits of a very close extraction
of gold, if the following requirements are carefully observed:
1st. The gold must always be in a metallic state. Quartz,
free from other earths and sulphurets, containing very fine
gold, can be subjected to chlorination without other prepara-
tion than moistening with water, as described further on.
Very hard quartz, causing a greater wear of shoes and dies,
may give a less favorable result, on account of the metallic
iron. Sulphureted ore requires a perfect roasting. The
presence of lead makes a careful roasting necessary, com-
mencing with a very low temperature. All metals, except
gold, must be transformed into oxides. Sulphates are injuri-
ous.
2d. The chlorine gas must be free from muriatic acid.
From the generator the gas is forced through clear water, by
which the muriatic acid is absorbed. The muriatic acid dis-
solves the oxides and causes, when sulphides are present in
consequence of defective roasting, the formation of sulphu-
reted hydrogen, by which the soluble chloride of gold is pre-
cipitated. The muriatic acid dissolves also oxides of metals,
which are precipitated by the addition of sulphate of iron
with the gold.
Before a detailed description of the chlorination process is
given, it will be, in some cases, of importance to become
acquainted with a simple mode of trying the process on a
small scale; for instance, on from five to twenty ounces of
sulphurets.
CHLORINATION.
227
SEC. 54.
Assay of Gold Sulphurets by Chlorination.*
Of the finely pulverized sulphurets, from five to seven
ounces or more, are weighed out and roasted on a piece of
sheet-iron, the edges of which are bent up, and the
inside coated over several times with clay-water, and then
well dried. The roasting may be performed over charcoal or
coke, in a small stove, or in a large black-lead crucible, through
the bottom of which a hole is cut for the draft. The sulphu-
rets must be stirred with an iron spatula until no smell of sul-
phurous acid is perceptible; after which a tolerably strong
red heat is applied. When cold, the sample must be ground
over in an iron mortar and roasted once more at a red heat.
When no sulphurous odor is observable, the roasting may be
considered as finished.
•
When cold, the roasted ore must be moistened with suffi-
cient water in a dish or cup, to make it of a loose or wooly
consistence, in which state it is best suited for chlorination.
If the roasting was perfect, the metallic gold can be dissolved
in chloruretted water and extracted, but in case there was in
the roasted stuff a small quantity of sulphurets or arseniurets
undecomposed, it is more proper to use chlorine gas. The
extraction is performed in the following way:
In a glass cylinder, C, Fig. 3, Tab. VII, from eight to ten
inches high, two and a half inches wide, provided with a neck,
b, near the bottom, about three-quarters of an inch wide, is
introduced a layer of small clean quartz fragments, as shown
in the drawing, and on this a thin layer of coarse and then
fine quartz sand. This quartz forms the filter. Over the
quartz is then placed the roasted and moistened ore, as loosely
as possible. The cylinder has a cover of wood or of India-
*Plattner's Probier Kunst.
†Pulverized glass answers perfectly.
228
CHLORINATION.
rubber, in which a glass pipe is fixed, as represented by c.
The longer end dips into another cylinder, containing rolled
stiff blotting paper or pieces of blotting paper, or shavings of
wood, moistened with alcohol, before the gas enters the
pipe, c.
For the generation of the chlorine, say for twenty ounces
of roasted sulphurets, a glass vessel, A, (about two inches in
diameter) is charged-
With 1 ounce manganese (peroxide) pulverized,
((
66
4
(( 1
1
แ
muriatic acid,
sulphuric acid, mixed with
of water.
This mixture is shaken up and the vessel placed on a cup
or on a piece of sheet-iron covered with sand, and the
neck corked. Through the cork a glass tube, a, is fixed so
that it reaches about two inches below the surface of the
water contained in the bottle, B. (The glass tubes are easily
bent to the required shape, when heated by the flame of an
ordinary alcohol lamp.) The chlorine gas is forced through
the water, and by this means washed from muriatic acid. It
is then conveyed through the pipe, d, into the ore receiver, C.
The apparatus is more conveniently arranged if the three
tubes, a, d, c, are made in two parts each-the first and last
to join at a and c, by short India-rubber tubes. The tube, d,
is connected below, near the cork, b, so that its short horizon-
tal part will serve for the discharge of the lixivial when dis-
connected. As the chlorine is not only disagreeable but also
injurious, it is necessary to cover all corks and joints with
wheat flour dough (using wet fingers). The above quantity
of sulphurets (twenty ounces) requires about two hours roast-
ing and a receiver, C, six inches high and four inches in diam-
eter, or other dimensions of the same content.
The operation can be performed in a room without molest-
ation from the chlorine, because, with the alcohol in the
cylinder, D, it forms "chloral" and muriatic acid, which are
not annoying.
The mixture in the vessel, 4, must be moderately heated
CHLORINATION.
229
in the beginning. The gas appears of a greenish color, and
will soon fill the cylinder, C. By this time the finest gold is
transformed into chloride, but this is not the case with the
coarser particles and with such gold as may be contained in
undecomposed sulphurets. For this reason the development
of the gas must continue for at least one hour more, before
the chlorination is finished. If auriferous pyrites is operated
upon, the apparatus can be taken apart, commencing always
with the tube, a, else the water from B would be drawn over
to A. If compound ores (galena, zinc, etc.,) with free gold
are under treatment, the bottle, A, is separated from the
apparatus which remains undisturbed for at least fifteen hours.
After this time, when all is taken apart, warm water is care-
fully introduced over the ore, in order to lixiviate the chloride
of gold and other soluble salts. The cylinder must be a lit-
tle inclined, so that no fluid remains on the bottom, and if
the neck should be a little too high above the bottom, this
can be filled level with the outlet by pitch.
The obtained solution must be mixed first with a few drops
of muriatic acid; then a clear solution of sulphate of iron
(green vitriol) in sufficient quantity added, and stirred with a
glass staff. The whole is allowed to stand (if possible, warm)
till all the gold is precipitated and the solution clear. If a
few drops of the sulphate solution should effect a slight pre-
cipitate when added to the clear fluid of the precipitated
gold, it would prove that too little of the precipitant was
used. The solution and precipitated gold are introduced into
a filter, and washed with clean water; then the gold is dried
with the filter in a porcelain cup over an alcohol lamp. The
dry filter, carefully folded, is then placed in a red-hot muffle,
either in the same porcelain cup or in an assayer's dry cup,
and burned with free access of air. When cold, the ash is
mixed with one or two hundred grains of test-lead and cupel-
led under the muffle, and the gold button weighed. If we
have under treatment gold quartz which contains only fine
gold and no sulphurets, the roasting is not required; but it
is necessary to extract the metallic iron, which results from
230
CHLORINATION.
pulverizing in an iron mortar, by means of a magnet. In
place of the cylinder, C, if such cannot be obtained, a bottle,
the bottom of which is cut off by means of a string, as repre-
sented in Fig. 4, will answer the purpose. Or a wooden
box of a square section could be substituted for the cylinder,
provided the inside is carefully coated with pitch or asphal-
tum cement.
SEC. 55.
Chlorination Process for Sulphurets and Arseniurets.
The operations to which concentrated sulphurets or arseni-
urets are subjected, are principally the following: 1st. Oxid-
izing or chloridizing roasting in reverberatory furnaces. 2d.
Impregnation of the roasted ore with chlorine gas in wooden
vats. 3d. Filtration of the soluble parts by cold water. 4th.
Precipitation of the chloride of gold by sulphate of iron.
The finer the sulphurets are, the easier and quicker the
chlorination will be performed. It is, however, not necessary
to pulverize the concentrated stuff still finer; it may be ope-
rated upon as it is obtained from concentration. The chlori-
nation process requires no motive power.
The presence of galena and of copper sulphurets do not
interfere with the chlorination, provided the roasting was
well performed. Gold of very low fineness, containing from
forty to fifty per cent. of silver, will probably resist the chlo-
rination, unless it is in the finest state of pulverization.* The
formation of chloride of silver would prevent the thorough
chlorination of gold particles. The silver combined with the
gold is not obtained by the chlorination process, but the pure
gold only, for the reason that the amount of silver is generally
too insignificant to admit of a remunerative extraction by a
*Very low gold, in which the amount of silver would prevent the chlorination of
gold, by forming an impenetrable coating of chloride of silver, can be treated by a
chloruretted solution of salt, which dissolves the chloride of silver and that of gold,
as described further on.
CHLORINATION.
231
hot solution of salt. Coarse gold requires too much time to
be converted into a chloride, and therefore the ore contain-
ing such gold is unfit for chlorination. Pan-tailings of con-
centrated sulphurets allow an easy and perfect extraction of
gold by this process.
The presence of lime and talc (silicate of magnesia) make
the chlorination of roasted ore very troublesome, or even
impossible; but an addition of salt in roasting removes the
difficulty.
There are also some other troublesome substances in con-
nection with some sulphurets. Such, for instance, are found
near Jackson, Amador county, Cal. Although these permit
the chlorination after roasting, yet when a solution of sulphate
of iron is added for the purpose of precipitating the gold out
of the solution obtained, another substance of a white color is
likewise precipitated in such quantity as to render the smelt-
ing of the gold impossible. The nature of the white precip-
itate is not known to the author, as he has had no opportunity.
to obtain a specimen of it. An analysis of the stuff would
probably give an indication of the manner in which the roast-
ing process may be conducted, in order to obviate the precip
itate, or if this should prove insufficient, determine what might
be added to the filtrate to prevent such precipitate. It must
be supposed that the white precipitate caused by the sul-
phate of iron is also a sulphate, and can be thrown down by
sulphuric acid before using the sulphate. It is, however,
necessary to allow at least two hours for the precipitation
with sulphuric acid; this is especially required if there is a
great deal of lead in the ore and the roasting was performed
with salt. After the precipitate is deposited on the bottom,
the clear solution containing the gold must be drawn over
into another precipitating vat, and the gold precipitated by
sulphate of iron, or the gold is first precipitated by sulphu-
reted hydrogen, whereby lime, baryta, etc., which would be
precipitated as a white powder by the sulphate of iron,
remain dissolved in the solution.
The roasting is the most important part of the whole oper-
232
CHLORINATION.
ation-that on which the success of the chlorination princi-
pally depends. The concentrated sulphurets must be sub-
jected to roasting while damp, or at least before crusts and
lumps are formed by oxidation, in consequence of too long
lying. Pan-tailings of sulphurets, however, must be dried,
either artificially or by exposure to air and sun, and then pul-
verized by some means so fine as to admit of being sifted
through a sieve of from twelve to fourteen meshes to the run-
ning inch. If such tailings were subjected directly to the
roasting, they would bake into hard lumps, and the mass
would be rendered unfit for chlorination.
The construction of the furnace has but little influence on
the chemical result of roasting. The best construction is that
of a reverberatory furnace, where the flame of the fuel comes
into direct contact with the sulphurets. Furnaces like a
retort or a muffle, in which the sulphurets are exposed to the
oxygen of the pure air, give no better result; and the roast-
ing is more expensive, for the reason that more fuel is
required. In reference to time and cost of roasting, the
arrangement of a reverberatory furnace is important. There
must be, in accordance with the purpose, the proper propor-
tion between the height of the roof, the area of the fire-place
and the hearth, and the flue and section of the chimney.
In all furnaces, at the beginning of roasting at a low heat,
the sulphur of the sulphurets is set free, combining with the
oxygen of the air to volatile sulphurous acid, which is well
known by its sharp, suffocating odor. The metals, by losing
a part of their sulphur, are converted into oxides and princi-
pally into sulphates, in which the iron sulphates are predom-
inant. Sulphate of iron is the precipitant of the chloride of
gold; its presence in the roasted ore is therefore very objec-
tionable, and it is necessary to increase the heat by degrees,
in order to decompose the sulphates and to form oxides.
Similar to this is the behavior of auriferous arsenical pyrites,
when subjected to roasting. Arsenious acid escapes under
the influence of heat and oxygen, while oxides and arseniates
remain, the latter being further decomposed to oxides by
CHLORINATION.
233
increased heat. At the same time all metallic iron derived
from grinding or stamping, must be converted into an oxide.
After the sulphur and arsenic have been expelled, the gold
remains in a free, metallic condition, and can be easily detected
by pulverizing and washing a small portion of the roasted
stuff. While the formation of oxides and sulphates or arsen-
iates is going on, the gold is set free, and remains so during
the whole process. When salt is used in roasting, the gold,
according to Plattner, forms first chloride of gold (Au. Cl.³)
far below red heat. At two hundred degrees, C, it loses a
part of its chlorine, and changes into a sub-chloride (Au. Cl.)
at about two hundred and forty degrees, C. This sub-chlor-
ide is not soluble in cold water. At a red heat it is converted
into metallic gold.
The Loss of Gold in Roasting.-It has been stated that the
loss of gold in the roasting of gold ores in some places amounted
to a high percentage in some cases, even to one hundred per
cent. This, however, was not confirmed by the experiments
of Plattner, who exposed different combinations of gold, with
sulphur and arsenic metals, and different ores and other sub-
stances, as well as free gold, in the finest state to different
degrees of heat, for longer and shorter intervals of time; but
the result showed that a loss of gold occurred only when the
roasting was performed so rapidly that the finest gold parti-
cles were carried off by the volatile products of roasting.
Many other experiments showed that the loss of gold in
roasting is very inconsiderable. The results obtained in Cal-
ifornia confirm the same. Many tons of sulphurets have been
roasted for more than thirty hours without interruption, and
the result of chlorination has given ninety per cent. of the
gold, as compared with the fire assay. The tailings always
contained some gold, so that very little or none of it was lost
during the roasting.
It has also been stated in California (perhaps taken for
granted) that an addition of salt causes sometimes a loss of
gold.
This also seems to be contradicted by the recent pro-
16
234
CHLORINATION.
ceedings in Grass Valley, where five per cent. of salt has been
used on the concentrated sulphurets with a very satisfactory
result.
Before the practical operation of roasting is described, it
appears necessary to explain some of the most suitable
furnaces.
SEC. 56.
The Roasting Furnaces.
Single Roasting Furnaces.-Fig. 5 (longitudinal section) and
Fig. 6, (horizontal section) Tab. VII, show a roasting furnace
for one ton of sulphurets at a charge. a, is the hearth bot-
tom, about twelve feet square. It is made of the hardest
bricks, laid edgewise, close together, forming a stratum of
four inches in thickness. It is not necessary to stir the sul-
phurets continually, as is often done with silver ores, for this
reason, the bottom is sometimes made by laying the bricks
flat, directly on the mass of loam or gravel which was taken.
to fill up the space between the outside walls. Such a bottom
will stand for many months, but not so long as one built of
bricks laid edgewise. There are four working doors, c, c,
which enable the roaster to reach all points of the hearth con-
veniently with light, because shorter, rakes. In the middle
of the length of the bottom, nearer to the doors towards the
chlorination vats, is a square discharge hole, b, which is kept
shut by a slide, d, during the roasting.
Below the floor is an arch through the whole width of the
furnace, through which the hole, b, passes. An iron car on
rails receives the roasted ore when discharged, and wheels it
to the cooling place.
The bridge, e, is from ten to twelve inches wide, and from
eight to ten inches high. It separates the hearth from the
fire-place. If possible, the bridge ought to be made of two
or three pieces of soap-stone, sandstone or granite, which is
CHLORINATION.
235
not liable to burst when heated by degrees. The bricks are
often damaged by the hoes in stirring the sulphurets, and
require frequent repairs. The outside wall, f, is often made
twelve inches thick, but it is always better to give sufficient
substance to the wall, on account of heat, and at the same
time to obtain a strong support for the roof; the thickness.
ought, therefore, not to be less than twenty-four inches.
Economy here is misplaced.
The roof is generally twenty inches above the bottom, as
the greatest distance; if it is less, although the form of the
furnace is improved, it is less likely to be durable, unless the
work is perfect. The length of the bricks gives the thick-
ness of the arch, that is, eight inches. This arch, if all the
bricks are placed perpendicularly, will stand a great deal longer
than one of twelve inches in thicknsss, when the bricks are
laid with the long sides alternately horizontal and perpendic-
ular.
There are three circular openings, h, h, in the roof, each ten
inches in diameter, communicating with the chimney by the
flue, i, opposite which is a small door, k, for the purpose of
cleaning the flue, i, from time to time. For the same purpose
an opening must be prepared in front in the direction, as
shown by m. The best way to regulate the draft is by means
of a cover, n, on the top of the chimney, but when there are
two or more furnaces to one chimney, a damper in the flue, i,
will answer the purpose.
The sulphurets are charged through the roof at o. It is of
importance to secure the furnace against expansion with grap-
pling irons, of which there are eighteen. The iron rods cross-
wise, are from five-eighths to six-eighths of an inch in diame-
ter; the others, p', which are placed over the length of the
furnace, are stronger-one inch. The grapplings are repre-
sented on a large scale in Fig. 11, made of cast-iron, about
four feet long. For the passage of the rods of the lower ends,
square holes (r, Fig. 5,) are provided through the masonry of
the furnace. Another sort of grappling is shown by Fig. 12.
They are made of wrought-iron, and must be at least one inch
236
CHLORINATION.
thick. They are cheaper than the cast-iron ones, but the lat-
ter are preferable.
Double Furnaces. This style is shown by Fig. 9, Tab. VII.
The heat which escapes from the single furnaces is conveyed
in Fig. 9 through the flue, e, over the upper hearth, b, of the
same size, having the working door on the opposite side. On
this second hearth the ore loses a great deal of its sulphur,
and is drawn through a discharge hole in the middle of the
floor on the lower hearth, where the roasting is finished.
From 6, the heat must pass a third hearth, a, before it enters
the chimney. It is rather a drying than a roasting place, as
the heat is very moderate. Some furnaces of this kind have
an auxiliary fire-place for the second hearth at d, which, for
the roasting of auriferous pyrites, is entirely superfluous, but
would assist in a chloridizing roasting of silver ores.
In Freiberg, Saxony, there were three double furnaces for
the roasting of lead ores for smelting purposes. These three
furnaces have been combined into one, as represented by
Fig. 10. The heat passes the lower three hearths, and then,
ascending through the flue, the upper ones. From the flue,
a, it is conducted over the drying hearth, b, built in the same
way as a, in Fig. 9. From b, the ore is drawn on the next
lower hearth, c, and is removed after two hours to d, where it
is again exposed to the heat for two hours. Every two hours
the ore advances a step till it arrives at e, where the strong-
est heat has now already a half smelting effect upon it.
Every two hours one charge of eight hundred pounds of roasted
ore is obtained from the hearth, e. The lower furnaces have
two working doors each, the upper one three. There is
not much stirring in this operation, and a sort of shovel is
more in use than the hoe. The fuel used is coal.
A different construction is shown in Figs. 7 and 8. The
first is a vertical section, the second a horizontal one. This
furnace was built by Mr. Deetken, in Grass Valley, Cal., for
the sulphurets from the Eureka mine. The construction is
like that of the roasting furnace at Pontgibaud, for lead ores.
CHLORINATION.
237
The upper hearth is not above the lower, but a continuation
of it, interrupted by a step-flue, a, of seven feet ten inches in
height-in the drawing, less. The upper hearth is six feet
wide by thirty-nine feet in length, furnished with working
doors upon each side, twelve in number.
One of the doors of the upper hearth is shown in Fig. 17,
of a simple and very suitable pattern. The chimney, b, about
twenty-five feet high, is built after Deetken's cheap plan, of
four inches thickness-twenty-eight inches each side in the
clear. The way of roasting is explained further on.
This kind of furnace requires more room than the double
furnace (Fig. 9), but the work of stirring is less tiresome, as
the roaster is not obliged to step constantly up and down.
Another advantage is the extent of the upper hearth, which
receives nine tons of ore without difficulty; whereas the
charging of a three or four story high furnace, is very trouble-
some, if not favored by a sloping locality. Very much to be
recommended is also the Freiberg plan (Fig. 10), which
amounts to the same thing as Deetken's furnace, as the upper
hearths can continue on the same level with the lower ones,
if made advisable by local circumstances. The rising flue, a,
Fig. 7, is not necessary; on the contrary, it consumes a part
of the heat uselessly. There is also no special advantage in
making the second hearth narrower; for although the heat is
more contracted, the length must increase for the same quan-
tity of sulphurets.
These furnaces are a great deal more effective than the
single furnaces. For the purpose of roasting sulphurets,
where the capital is limited, a furnace ought to consist never-
theless of at least three hearths, constructed like Figs. 5 and
6, but arranged similar to the lower tract of Fig. 10. By
this means it is possible to draw every ten or twelve hours a
ton of roasted sulphurets from the hearth near the fire-place.
In reference to a mechanical furnace, it is very questionable
whether any advantage could be derived therefrom in roast-
ing sulphurets for chlorination. Long experience in Cal-
ifornia has proved that a certain length of time, about twenty
238
CHLORINATION.
hours, is required to finish the roasting of one charge of two
thousand pounds of sulphurets, and that by employing three
men in place of two, in order to have the stirring more dili-
gently performed, the time of roasting cannot be shortened.*
The only way of shortening the time is by the use of long fur-
naces in which a great quantity of stuff is gradually prepared
by being moved in successive portions towards the fire-place.
If, as is claimed by different furnace patentees, the roasting
of sulphurets could be performed in much shorter time, with
the same precision as is now done in twenty-four hours, which
is not impossible, it certainly would be much cheaper work,
as the roasting expenses at present amount to over 50 per
cent. of the total cost of the chlorination; but practical proof
is necessary.
SEC. 57.
The Roasting Operation.
The performance of roasting the sulphurets or arseniurets
is very simple; the principal aim must be directed to a per-
fect, dead roasting, that is, the expulsion of all sulphur.
After the furnace has been heated for some hours, the sulphu-
rets are introduced through a hopper above the roof into the
furnace, and spread over the hearth. A furnace like Figs. 5
and 6, Tab. VII, takes one ton at a charge. One man is suf-
ficient to attend the furnace. The fire is kept moderate, as
the burning of the sulphur creates so much heat that nearly
half of the sulphur contained, is expelled thereby. On expos-
ing a new surface of the mass (which, in a short time, becomes
dark-red hot) to the air, the burning sulphur with a bluish
light can be seen distinctly. The hoe is principally used for
stirring. It must be as light as possible, and is represented
by Fig. 19, Tab. VII. The plate, a, is made of boiler-iron,
ten inches by four and a half and one-eighth of an inch thick,
*According to Mr. Deetken.
CHLORINATION.
239
and riveted to the round iron rod, six-eighths of an inch in
diameter and seven to eight feet long,-one or two on each
side of the furnace. The stirring is performed at intervals
of about fifteen minutes. Whatever is said about the useless-
ness of continual stirring, the fact must not be overlooked
that sulphurets exposed to the air are sooner deprived of
their sulphur, than those which are nearest the hearth and
excluded from undecomposed air. If this were not the case,
even a partial stirring would be useless. For that reason the
intervals must be only of such length as is necessary for the
relief of the roaster.
In proportion as the oxidation of the sulphur and iron draws
nearer to the end, the temperature decreases, and it is neces-
sary to use more fuel, so as to keep the mass at a good red
heat. It takes from twenty to twenty-four hours before the
roasting of one charge may be considered finished. If it
should be observed that in throwing up the sulphurets in the
furnace by means of the hoe or shovel, many brilliant sparks
appear, it would indicate that the roasting was carelessly per-
formed; and it must be continued until this appearance
ceases.
In a double furnace, Figs. 7 and 8, the heat in the lower
hearth is always kept bright. One ton is roasted below, and
about nine tons are spread on the upper long hearth. There
are two roasters busy at the same time; one with the finish-
ing, the other with the preparatory part, but assisting each
other if needed. When one charge is drawn into the iron car
below the hearth, the other load is pushed down from the
upper hearth, c, through the flue, a, shortly beforehand, and
is now ready at d, to be drawn into the furnace by means of
hoes through the doors, e, e. There is another door, g, behind
the flue hearth for the same purpose. This charge was
exposed to the preparatory roasting for about twenty-four
hours on the upper hearth, and consists of a small part of
undecomposed sulphurets, and of oxides and sulphates. At
a lively heat and with active stirring at intervals, all the base
metals ought to be converted into oxides, after twelve hours'
240
CHLORINATION.
work, and the charge taken out. In this way it is possible to
obtain two tons of well roasted sulphurets in twenty-four
hours.
As soon as the charge from c, is removed into the lower
furnace, in which both roasters are engaged, the sulphurets
from h, must be removed to c, from i, to h, and so on, until the
end of the hearth at k, is ready to receive a new charge of
one ton through the charge-hole in the roof. Although the
temperature is very low, the whole mass on the upper hearth
assumes a glowing condition, in consequence of the burning
sulphur. The roaster performs his stirring regularly from c,
to k, or the reverse, from both sides of the furnace. The
hoes are made of five-eighths round iron, and six feet long, for
the upper hearth.
Whatever shape a reverberatory furnace may have, the
final roasting is always performed nearest to the fire-place.
Roasting with Salt.—An addition of salt in roasting sulphu-
rets is not injurious to chlorination, but it increases the
expense uselessly if mixed with such sulphurets where there
is no necessity for it. If the ore from which the concentrated
sulphurets are obtained contains lime, calc-spar, talc, or heavy
spar, it is necessary to introduce a chloridizing roasting. In
all other cases experience must decide. It is, however, also
easily ascertained by an experiment, on a small scale, as
explained in §54, by two comparative assays, one of which is
roasted with five or six per cent. salt, the other without. The
result will show which mode is preferable. Lead and anti-
mony do not allow the use of salt in roasting.
It is sufficient to add five per cent. of salt, that is, one hun-
dred pounds to a ton of sulphurets. It is plain that salt is
more effective when pulverized than when used in a coarse
state, but it is immaterial whether the mixture is made on the
upper hearth, or whether the salt is added when the charge
is exposed to the finishing-roasting, as there is no action of
the salt, or very little, in the dark-red heat of the upper
hearth; but if the roasting is performed in a single furnace,
CHLORINATION.
241
where the heat is less under control, it might be better to
introduce the salt by means of scoops into the furnace five or
six hours before the end of the operation. The salt must be
well mixed with the ore.
The roasted ore, when in the car, is wheeled to a cooling
place which, if possible, must be so much below the floor of
the roasting department, that the contents of the car may be
dumped and spread out. After the roasted ore is cooled
down, it is removed to another compartment, for the purpose
of moistening. It is then subjected to the chlorination.
SEC. 58.
Chlorination.
1. Damping of the Roasted Ore. The roasted ore cannot
be treated at once with chlorine gas, for two reasons-first,
because the sulphurets, if dry, form a more condensed mass
than if in a certain damp condition, and are therefore more
obstructive to the ascending gas; and second, for the more
important reason that the chlorine does not act as vigorously
on dry as on damp ore. It is therefore indispensable to
moisten the sulphurets, after they are sufficiently cool. For
this purpose the roasted charge, or several tons, is spread in
a compartment of eight or ten feet square with sides two feet
high, of thin boiler-iron, and the water conducted over it by
means of a hose or otherwise. It may require from four to
five per cent. of water. The wetted surface is then turned
over several times, and mixed with the dry stuff beneath, till
it appears nearly uniform. The moistened charge must not
create the slightest dust, but, at the same time, the hand
should remain dry and clean on handling it. A handful of it,
pressed hard together, must form a lump which can be held
in the fingers, but falls into its former loose condition if hand-
led. Should it appear too dry, some more water, or in the
reverse case, some more dry ore, must be added and mixed
with it.
242
CHLORINATION.
Further on it will be seen that the vats in which the chlo-
rination is performed, contain a false bottom, on which a filter
is prepared. After a charge has been removed, this filter
contains a great deal of moisture, which draws into the newly
moistened charge, rendering the lowest stratum too moist;
whereby it settles somewhat and hinders the free access of
the introduced chlorine. To avoid this, some dry ore is spread
over the filter, that is, the bottom-say eight or ten inches
deep, and allowed to lie for six or eight hours. Should it be
found too dry or too wet, it must be made right by the addi-
tion of moistened or dry stuff, as the case may be. A short
experience will teach one to introduce the proper amount of
roasted ore necessary to take up the moisture. This charged
part as well as the moistened, as described before, must be
subjected to-
2. Sifting. This operation takes but a short time, and is
necessary for two reasons. One is the separation of lumps
and crusts formed during the roasting, and of other impurities
which might drop in accidentally, all amounting to two or
three per cent. The other reason is the required loose con-
dition of the ore in the vat, which is best obtained by passing
it through a sieve. For this reason the sifting must be per-
formed directly into the vat. The sieve is twelve to fourteen
inches by twenty-five in the clear,-the sides five inches high.
The sieve is sufficiently fine, if there are seven to eight meshes
to the running inch.
A chlorination vat, into which the ore is sifted by pushing
the sieve to and fro, either on two scantlings laid over the rim
of the tub, or suspended on four ropes, is represented in Fig.
13, Tab. VII. It is a vertical cross-section of a circular vat,
seven feet in diameter, capable of holding three tons of roasted
sulphurets.
Above the bottom, b, is an empty space over the whole bot-
tom, one inch high, formed by the false bottom, a, the boards
of which are laid together, leaving about one-eighth of an inch
space between them.
Besides this, there are half-inch
CHLORINATION.
243
A
holes bored in it, from ten to twelve inches apart. The boards.
are supported by short pieces, c, leaving sufficient space for
the passage of the chlorine. Over the false bottom is spread
first a layer of clean quartz from one and a half to two inches
in thickness. In default of quartz, another kind of rock will
answer the purpose, provided there is no lime or talc in it-
which would absorb a considerable amount of chlorine; and
if notice is not taken of the character of the rock, the great con-
sumption of chlorine might be supposed to be the consequence
of defective roasting. Over the coarse layer smaller pieces.
are laid, and so on, decreasing in size, till a layer of sand cov-
ers the whole, forming thus a filter of from four to five inches.
in thickness. This filter remains always in the vat; the shov-
eling out of the residue, therefore, must be done carefully, on
approaching the filter bottom. There are two holes commu-
nicating with the space below the false bottom. One is for
the reception of the lead pipe, d, by which the chlorine is
introduced; the other is provided with a leaden cock, e, for
the discharge of the lixivium. This side of the vat stands
one-half of an inch lower.
The wooden vat would absorb a great deal of the gold in
solution, if the inside were not coated with some material
which prevents the soaking in of the fluid. Mr. Deetken uses
one part pitch melted with one part of tar.
This is a cheap
and quite suitable mixture, and is applied by means of a brush
when hot. It is a matter of course also that the boards of the
false bottom should be coated carefully on all sides, as well as
the whole of the inside.
There are also vats or tubs five feet in diameter, three feet
high, holding two tons of roasted sulphurets. Three or more
of them are arranged in one row, as shown by Fig. 18, a, a.
They are conveniently managed, and preferred where small
charges of custom ore are to be treated.
Deetken introduced successfully a large vat of ten feet
diameter, two feet high, constructed exactly like Fig. 13.
This vat is capable of holding from six to seven tons of roasted
sulphurets. The usual charge is six tons. There is doubt-
244
CHLORINATION.
less more economy in treating six tons in one vessel than in
two or three of a smaller size; there is less waste of material,
and some saving of labor, with the larger size.
Chlorination vats with a greater diameter are preferable to
higher tubs of the same capacity; for the reason that a low
column of sulphurets assumes a less dense condition, and also
because of the greater cubic content of the free space above
the sulphurets, which is filled with chlorine, so that an acci-
dentally greater consumption of the gas can be replaced.
The cover, g, Fig. 13, must fit as well as possible in the
step of the vat side, but not too tight; the planks, however,
have to be fitted together tightly with tongue and groove.
For the purpose of lifting, there are generally three or four
chains fastened to the cover. Ropes are of no use, as they
are destroyed in a short time by the gases.
The moistened ore, as before said, is sifted directly into the
vat over the filter. In order to avoid a condensed charge, it
is necessary to move the sieve from one place to another, till
the whole charge is introduced; the surface is then made
even, and the charge is ready for chlorination.
3. The chlorine gas is produced in a leaden vessel, as shown
in Figs. 14 and 15; the first is a vertical cross-section, the
second a top view with the cover on. The circular tub, a,
has an outer ring, c, six inches deep, for the reception of the
ring-shaped side of the cover, b. A similar small ring, d', is
on the top of the cover, which receives the collar, e, fastened
to the leaden stirrer, f. There is also a short leaden pipe, g,
bent in the shape of the letter s, through which the sulphuric
acid is introduced.-the outer end forming a funnel for this
purpose. Another lead pipe, d, conveys the chlorine to the
vat. The cover is taken off, and for a charge of three tons
of roasted sulphurets is introduced the following:
30 pounds of manganese (peroxide) pulverized,
30 to 40
เ
75
6 6
45
((
"
"common salt, according to quality,
sulphuric acid, of 66 degrees, and
"water.
CHLORINATION.
245
The water, salt and manganese are introduced first, and
the generator covered. The two rings, c and d', are filled
with water and thereby the contents of the generator shut up
air tight, with the exception of the two lead pipes, g and d,
of the cover. The gas generator stands over a small furnace,
as represented by b, Fig. 18. The sulphuric acid is now
introduced through the pipe, g, Fig. 14, but not all at once.
Three bottles are generally sufficient to create so much heat
that the development of the gas takes place in sufficient quan-
tity. No fire is yet made under the generator. The chlorine
is not conveyed directly to the chlorination vats, but through
a purifying apparatus, as represented in Fig. 16. An ordin-
ary wash-basin or some other similar vessel, a, receives two
lead pipes (three-quarter inch). One of them, d, conveys the
chlorine from the generator, and is bent a little upward. The
other is bent in the same way, but stands higher. Both ends
are covered with a bottle, the bottom of which is cut off.
There is sufficient clean water in the dish to stand one-half or
three-quarters of an inch above the mouth of the pipe, d, so
that all gas which enters the space in the bottom is forced
through the water,—which takes up the muriatic acid. The
chlorine passes then through the pipe, d",-which is as long
as may be required by the distance of the vat, enters the
space below the false bottom, and gradually permeates the
ore. The water through which the gas passes absorbs, if
cold, about two and a half volumes of the chlorine, and is then
saturated; but is still good for the purpose of taking up muri-
atic acid. The warmer the water is, the less chlorine is
absorbed. It is therefore wrong to introduce a continual
stream of cold water into the wash-basin, a, as is done in some
places, as a good deal of the chlorine is lost thereby. The
water in the basin may be renewed once or twice during the
operation with warm water.
This apparatus is not only for the absorption of muriatic
acid, since, if a portion of this should happen to enter the
*The leaden gas generator costs about $120. The bottom is made of 16-pound,
and the sides and cover of 8-pound sheet-lead.
246
CHLORINATION.
vat, and, forming sulphuretted hydrogen, precipitate metallic
gold, this would be converted again into a chloride in pres-
ence of abundant chlorine,—but the apparatus is an indispen-
sable indicator of the progress in the gas generator. The
bottle, b, Fig. 16, must show a greenish gas, and the bubbling
from the pipe, d, must be very lively. If this should not be
the case, another bottle of sulphuric acid must be introduced;
and the addition continued as often as the development of the
gas becomes weaker. After the last bottle has been used up,
a moderate fire must be made below the gas generator. The
arch, c, Fig. 18, is very flat, and only two inches thick in the
middle. Care must be taken to have a half inch layer of sand
over the arch. An open crack would cause the melting of
the bottom of the lead vessel. It is also necessary to turn the
stirrer, f, now and then carefully, to prevent the caking of
the ingredients.
The vat, after the ore has been sifted in, as before described,
is left uncovered. It takes from three to six hours before the
gas reaches the top of the charge. The progress can be easily
watched by taking samples from underneath the surface.
The smell of the chlorine shows how high it has penetrated.
When the chlorine odor is perceived within a few inches of
the surface of the charge, the cover is laid over the vat, and
the edge, i, Fig. 13, all around the cover, luted with dough of
wheat flour. If there be any cracks in the cover, they must
be carefully pasted so that no chlorine can escape anywhere.
The only opening not shut, is a hole of one inch diameter, k;
but as soon as the gas commences to escape, that is plugged
up, and secured with dough. The circular opening, 7, in the
cover, is only proposed by the author, and explained further
on.
The chlorine is now permitted to operate on the gold for
twelve to eighteen hours. (It may be added that, as the sift-
ing requires some time, if the charge amounts to three or six
tons, the gas generator can be put in operation before the vat
is entirely filled with ore; because the ascension of the chlo-
rine is also slow.) The pipe, d", is removed and the hole
plugged up.
CHLORINATION.
247
All the apparatus must be examined at intervals, to see
that there is no loss of gas, or at least whenever such loss
should be perceived by the odor. For this purpose ammonia
serves. A glass rod dipped into it and carried close around
the place where the loss is indicated by the smell, will imme-
diately give off white fumes when in contact with the chlo-
rine, and show the place where it escapes. To prevent the
drying of the dough around the cover, it may be covered with
strips of wet cloth. For the production of chlorine the fol-
lowing is also used:
1 part manganese,
2 parts muriatic acid,
1 part sulphuric acid, diluted with 1 part water.
4. Lixiviation.-After twelve, or if the sulphurets con-
tain coarser gold, after fifteen to eighteen hours, the cover
is taken off and water introduced. If it should happen that
in taking off the cover no gas is found over the ore, it is advi-
sable to shut the vat and to impregnate the ore again with
chlorine immediately; as, in nine times out of ten, the extrac-
tion of gold will fall short. This, however, does not occur often
with proper management. The water should flow in quickly,
and in such a way as not to strike on one point,-producing
a deep hole in the mass. The cock, e, is shut, and the water-
flow continues until the surface of the charge is covered, and
no air bubbles appear. The water is then stopped, and the
cock, e, opened. A small stream of water into the vat, must
replace as much as flows through e, so that the surface of the
ore is always covered.
The respiration of the chlorine is injurious; and it is there-
fore advisable to avoid the inhaling of the gas as much as
possible by leaving the room until the gas disappears. The
best way would be to have an arrangement by which the gas
is carried out of the building; for instance, to put a movable
wooden pipe six inches square about the proposed opening, l.*
*More convenient would be a lead-pipe through the side of the vat, near the top,
through which the gas is forced by the entering water out of the building. In this
case the water would have to be conveyed by an India-rubber hose through the
opening, , of the same size with the hose.
248
CHLORINATION.
In order to prevent the stream of water from making a
hole into the ore, a perforated wooden distributor fixed to the
cover, as shown in the drawing, would answer the purpose.
A trough below the cock, e, receives the solution, and con-
veys it into the precipitating tub (c, Fig. 18). The trough
must be lined with sheet-lead, avoiding sharp corners, or it
must be at least well coated with tar and pitch, in default of
sheet-lead. Great care must be taken to prevent the waste
of the solution. Not a drop of it ought to be seen outside of
the trough.
The precipitating vat, e, Fig. 18, is a wooden tub, like the
chlorination vat, Fig. 13, but without a false bottom. The
staves must fit together perfectly. One four feet in diame-
ter and three feet high, is sufficient to receive the solution of
three tons of ore. Deetken's ten foot vat, containing six tons
of sulphurets, requires two precipitating vats; one is five
feet, the other six feet in diameter, each two feet high. The
vats ought to be lined with sheet-lead, and a more proper
shape would be a rectangular box with a half-round, some-
what inclined sheet-lead bottom, which permits an easier and
better cleaning. In default of a leaden lining, the vats must
be coated with a mixture of pitch and tar; otherwise the
wood absorbs some of the gold solution. A better and
smoother coating is obtained by the use of the so-called
"asphaltum cement," which should be applied twice before
it is ready for use, as the cement is too liquid for a single
coating. A very smooth surface of the vat is important, else
it is difficult to gather all the finely precipitated gold.
From time to time samples are taken in a clean tumbler of
white glass from the solution at the end of the trough, and
observed in reference to the point whether an addition of a
clear solution of sulphate of iron (green vitriol) causes a dark
precipitate. If the solution after the addition of the precipi-
tant should remain perfectly clear, the water supply in the
chlorination vat must be stopped, and all the liquid contents
of the vat permitted to flow into the precipitating vat.
5. Precipitation.-The precipitant for the gold is a solu-
CHLORINATION.
249
((
tion of sulphate of iron. It is known also under the name of
copperas," or green vitriol, and forms light green crystals.
Dissolved in water (in a barrel twenty or twenty-two inches
diameter, and about three feet high) it generally makes a
muddy solution, and gives a light sediment, which must not
be disturbed in drawing off the clear solution from above it.
For this purpose a leaden syphon will answer. It is, however,
better economy to prepare the precipitant fresh, in the chlo-
rination works. In a barrel or tub of about ten cubic feet
content, fifty to sixty pounds of pieces of old wrought-iron are
introduced, then five or six buckets of water, and twenty to
thirty pounds of sulphuric acid. This is prepared two or
three days before the solution is wanted. One or two buck-
ets of this iron solution must be introduced into the precipi-
tating vat before the gold solution is allowed to flow in, so
that the precipitation may begin immediately. After this, as
much of the precipitant is added as is required, which can be
ascertained by taking a sample out of the precipitating vat,
filtering it through filtering paper, and mixing it with the
precipitant. If the mixture should darken a little after a
time, some more of the iron solution must be introduced into
the precipitating vat. The precipitated gold requires some
time before it is all deposited on the bottom. The fluid must
appear perfectly clear before the water can be drawn off.
Generally the mixture stands undisturbed over night. The
upper plug (e, Fig. 18,) is removed, and the clear liquid con-
veyed into another vessel, f, of sufficient capacity, till it is
nearly all run out of the precipitating tub through all the
plug-holes. The discharge must be performed carefully, so
that the flow appears always clear.
It is better if several chlorinations have been performed
before the gold is taken out, as there is a less percentage of
loss by wastage, with a large quantity of gold. This is dip-
ped out carefully by means of a dipper or scoop, into a clean
porcelain dish or enameled vessel, and the rest washed out
through the lowest cock. It is well to apply a jet of water
over the sides and bottom, in order to wash off all the precip-
itated gold.
17
250
CHLORINATION.
The gold obtained is then introduced into a filter of filtering
paper, and subsequently dried in an iron or porcelain vessel,
in a warm place or over fire. For the purpose of melting,
the black-lead crucibles are less suitable than "Hessian" or
clay crucibles; from the latter a purer gold is obtained. A
little salt, some borax and saltpetre (nitrate of potash), are
added as fluxes.
SEC. 59.
Cost of the Chlorination Process per ton of Ore.
If the ore is roasted in a long or double furnace ($56) a ton
of well roasted sulphurets can be drawn out every eight
hours, that is, three tons in twenty-four hours. The working
expenses of twenty-four hours may be given as follows:
Superintendence,.
Four roasters, at $3.50,
•
Three cords of wood, at $4,.
Thirty pounds manganese, at 61c,
Forty pounds salt, at c,..
•
Seventy-five pounds sulphuric acid, at 23c, .
One man at the vats two days, at $3.50, .
Sulphate of iron,.
Total cost of three tons,
Or, $14.55 per ton of sulphurets.
·
$ 6 00
14.00
12 00
1 87/1/20
30
1 87/1/2
7.00
60
$43 65
SEC. 60.
Remarks.
Zinc, Antimony and Lead are not obstructive to the extrac-
tion of gold by chlorination; but it is not as yet determined
by experience whether or not a great amount of galena would
to a certain extent prevent chlorination. By all means, the
presence of galena necessitates a good roasting, and a strong
CHLORINATION.
251
finishing heat, in order to decompose the sulphates as much
as possible. For ore of this kind, a roasting-furnace of thirty
to forty feet long, and nine feet wide is very advisable; as
all danger of the melting or caking of the galena is avoided
by the preparatory roasting at a low heat,—especially if there
is from twenty to forty per cent. of galena in the ore. The
fusibility of the galena makes a more diligent stirring neces-
sary. In case the roasting is not properly finished, the unde-
composed sulphurets and sulphates would absorb a great deal
of chlorine, and the formed chloride of lead and antimony
would be carried into the precipitating vat. Both are precip-
itated as a white powder (as chlorides) by the dilution with the
leaching water. It often occurs that such ore is accompanied
by lime or calcareous spar; in this case the lixivium will
contain chloride of lime which is precipitated with the gold
as gypsum, if not separated beforehand by the addition of
sulphuric acid. Heavy spar will probably behave like cal-
careous spar, and likewise be precipitated by sulphuric acid.
An experiment was made with two samples of ore. No. 1
had three per cent., No. 2 had thirty per cent. galena.
Twenty ounces of each sample were subjected to roasting
without salt for two hours, and then chloridized. No. 1 was
easily treated with the usual quantity of chlorine, and gave
85 per cent. of the gold contained. The tailings showed
coarse gold particles which could not be chloridized in twelve
hours' time. No. 2 absorbed nearly twice as much chlorine
as No. 1, and was leached after twenty-four hours. The
result was not satisfactory. Only sixty-two per cent. of the
gold was obtained; but the tailings, on examination, showed
undecomposed galena, which proved that the roasting time
was too short, or the heat too low.
The coarse gold of No. 1 was taken up instantly by the
quicksilver, in consequence of the clean surface created by
the action of the chlorine. It seems probable, therefore, that
if the chlorination tailings (in case they contain coarse gold)
were conducted over a few quicksilver rifles, properly
diluted, all the gold would be taken up. For the regular
252
CHLORINATION.
discharge of such tailings, the feed-box, §44, A, could be
employed successfully. No stirring of quicksilver is admis-
sable in this case; for the reason that "flouring" of the mer-
cury, caused by the chlorine, could not be avoided.
The question in regard to the utilization of the chlorine
which remains in the vat after the chlorination of the gold
has been finished, must be decided by a practical trial. A vat
of seven feet diameter and two feet high, when filled with roast-
ed ore to within six inches of the top, leaves about forty-seven
cubic feet of space for the chlorine. (The moistened stuff
contains more than fifty per cent. of interstitial space.) Pro-
vided the roasting was well performed on auriferous iron
pyrites, the whole free space in the vat will be filled with
chlorine, after the process of chlorination is finished. This
ought to be the case under all circumstances; and if the
roasted stuff consumes more gas than usual, it must be replaced
by an additional quantity. Having, then, two chlorination
vats, the communication between them for the purpose of con-
veying the chlorine from one into the other is easily obtained
by two lead pipes, each leading from the upper part of one to
the empty space (c, Fig. 13,) of the other, the pipes being
provided with cocks. As soon as the water is admitted
through a hose into the vat, the chlorine will escape through
the lead pipe into the other already prepared vat. It will
be necessary then to fix a glass tube (bent in the shape of a
horse-shoe) into the upper part of the vats, so that the height
of the water above the ore can be seen and regulated accord-
ingly.
The chlorine, transferred into the other vat, will require a
certain additional quantity* from the generator. The pecu-
niary advantage of this proceeding, even if successful, will
not be very important, as the cost of chlorine is only $1.35
per ton (unless increased by freight charges on a long dis-
tance); but from a sanitary point of view the matter deserves
consideration, as the chlorine is injurious to the respiratory
organs, and may induce consumption.
*A considerable part of the chlorine will be absorbed by the water which is
introduced.
CHLORINATION.
253
The plan of forcing the chlorine into the vat by a pump or
similar arrangement, in order to gain a few hours' time,
involves complications which are not desirable. If an inch
pipe is used (d, Fig. 18,) the evolution of the chlorine in the
gas generator can be increased, and thus the time shortened;
which, however, is not advantageous, if in the roasted ore
there are, besides the gold, other substances which absorb
chlorine.
SEC. 61.
Other Methods of Dissolving and Precipitating the
Gold from Sulphurets or Ore.*
The chlorination works at Reichenstein, Silesia, were erected
for the working of arsenical pyrites. The gold is extracted
by Plattner's chlorination process. The building contains
forty-eight earthen chlorination pots, of which twenty-
four are always charged with roasted ore, while the content
of the other twenty-four are undergoing chlorination. The
pots are strengthened with iron hoops, and so prepared that
for discharging they can be turned over on two journals.
The lower end is conical, and contains an earthen perforated
plate. There is a wooden cover with a small round hole in
it, on the top of the pot. The gas pipe communicates with
the conical end. The gas generators are also earthen pots
with leaden covers, twenty-five pounds each, provided with
an opening for the charge, and with a leaden gas pipe.
There are twenty glass globes, used as precipitating ves-
sels, standing on a sand bath. There are also ten bottles for
the production of sulphuretted hydrogen.
The conical part of the chlorination pots is charged with
small pieces of quartz, and covered with the perforated plate.
After the concentrated arseniurets are moistened (in winter,
with warm water), each pot is charged with one hundred and
*B. Kerl's Hüttenkunde.
254
CHLORINATION.
fifty pounds. The gas generators are covered and secured
air-tight with flour dough, and the gas pipes arranged to con-
vey the chlorine into a washing vessel, to free it from muri-
atic acid. Each generator receives thirteen pounds muriatic
acid, and seven pounds sulphuric acid, diluted with the same
quantity of water; and as soon as the chlorine is required,
seven pounds of manganese are added. The charging hole is
shut, and the fire started underneath the sand-bath.
After the chlorine has passed through the ore for an hour,
the pots are closed with the covers, and examined from time
to time to see whether the chlorine rises above the ore. This
is the case, when a glass rod, dipped in ammonia, creates
white fumes above the hole of the cover. After six to seven
hours, the impregnation is finished; and all the joints of cover
and pot are secured by dough, and the chlorine allowed to
act on the gold until the next day. The covers are then
taken off and water of fourteen to twenty degrees R. intro-
duced. Boiling water would absorb less gas and dissolve
more salts. The leaching is stopped as soon as about ninety-
six cubic feet of the lixivium from twenty-four pots is
obtained (from three thousand six hundred pounds of ore).
The lixivium from all the pots is conveyed into four vats,
beginning at the first, so that the fourth vat receives the
poorest leach. The very small quantity of gold contained in
this is not precipitated, but the fluid is used over again for
leaching the next day. The fluid from the other three vats
is drawn over into the glass globes which stand on a sand-
bath, in order to bring the temperature of the contents up to
twenty degrees R. Sulphuretted hydrogen, obtained from
bleistein (sulphide of lead obtained in smelting lead ores),
diluted hot sulphuric acid, is conducted into the globes until
the fluid appears perfectly black from precipitated sulphide
of gold. This remains warm in the vessel until the next day,
when the gold is found deposited on the bottom. From each
globe, the clear fluid is drawn into a filter by means of glass
syphons, the ends of which can be corked more or less tightly,
so that the supply can be regulated according to the capacity
and
CHLORINATION.
255
of the filter. That which goes through the filter, is conveyed
through cisterns filled with saw-dust, in order to absorb any
sulphide of gold which may have escaped. The precipitated
gold is finally washed into the filters. In the course of six-
teen days, three hundred and twenty filters containing sul-
phide of gold are obtained; these are dried and burned on
four large dishes, then boiled in aqua regia, filtered, and the
gold of the filtrate precipitated by sulphate of iron.
The precipitated gold is placed upon filters and washed,
first with diluted muriatic acid, and then with water. After
this the filters are dried and burned, and the gold melted with
borax and saltpetre in clay crucibles.
The quantity of concentrated arseniurets daily subjected to
chlorination is three thousand six hundred pounds, containing
about five-ninths of an ounce of gold per ton, so that not more
than from twenty to twenty-one pounds of gold is extracted
yearly.
At Schemnitz, Hungary, the tailings from the silver extrac-
tion by Ziervogel's method, are treated for gold by Plattner's
chlorination process. They contain 0.012 per cent. of gold.
The chlorine gas generator is made of cast-iron, with a leaden
hood, joined by flanges and bolts. The hood has three open-
ings; one for charging in the manganese, another for the sul-
phuric acid, and the third for the passage of the chlorine con-
ducting pipe. The gas enters first the washing vessel, then
a receiver, and thence passes through two pipes into the
earthen chlorination vessels. The lower end is contracted
like a funnel, and receives a filter of quartz sand, two inches
deep. The upper part of the pot is furnished with a clay
cover provided with an eduction pipe.
The tailings having been dried and slightly glowed, for the
purpose of destroying the basic salts, are moistened in the
usual way, and six hundred pounds introduced into each of
the four chlorination vessels. The chlorine is then introduced
through a pipe below the quartz filter, and continued until
the gas is distinctly perceived above the charge. The cover
is put on and luted with dough, so as to be air-tight, and the
256
CHLORINATION.
tailings are exposed to the action of the chlorine for twelve
hours. At the end of this time, warm water is introduced,
and the lixivial collected in large glass bottles, where the gold
is precipitated by sulphate of iron. The gold after being
separated from the fluid by filtering, is washed and melted
with borax and saltpetre in clay crucibles. The lixivium is
conducted into tanks containing old iron, for the precipitation
of the copper, which always contains a small amount of gold.
The residue, that is, the tailings, is mixed with lime and
reserved for smelting. The loss in gold is 18.21 per cent.
Calvert's Method for Auriferous Quartz.-This method is
based on the production of chlorine in the mass of ore. This
process is cheap,-it permits of the extraction at the same
time of both silver and copper, and is not injurious to the
workmen. The finely pulverized quartz is mixed with one
per cent. of manganese, charged into vats, and muriatic acid
added. In this condition the ore is kept closed in the tubs
for twelve hours. There is a false perforated bottom in the
tub, covered with some brush and straw. The mass is then
leached several times with the same water, and is then con-
veyed into precipitating tubs ;-where the copper is first
obtained by means of iron, and afterwards the gold,-the
chlorine having been driven off by heating the liquid, and a
solution of sulphate of iron added.
If there is silver in the ore, the chlorine is generated with
salt, manganese and sulphuric acid; taking six parts of salt
to three parts of manganese. The formed chloride of silver
dissolves in the salt solution, and is precipitated by copper
plates, the copper by iron, and the gold by green vitriol.
Kiss's method is based on the solubility of the chloride of
silver and protochloride of gold in a leach of hyposulphite
of lime; but its success in the extraction of silver and gold
has not yet proved quite satisfactory.
CHLORINATION.
257
SEC. 62.
Extraction of Gold, Silver and Copper.
Sulphurets, or ores containing sulphurets, cannot be treated
either with chlorine or with chloruretted water, without roast-
ing; no matter how fine the ore may be reduced. Besides
the great quantity of chlorine which would be consumed, in
either case, by the decomposition of sulphurets, there will
always be formed some chloride and sulphate of iron,—both
of which would precipitate the gold from its chloride if such
should be formed, and prevent its extraction. If silver and
copper are present, they are converted into chlorides.
The chloride of copper is soluble in water, and can be
leached together with the gold; but the chloride of silver
remains undissolved in the residue ;-it is however soluble in
a concentrated salt solution. If, therefore, chlorine is con-
ducted through a salt solution* to saturation, this chloridized
solution dissolves gold, silver and copper at the same time, if
the ore containing such metals is treated therewith. On this
principle, Patera and Roeszner subject auriferous silver ores
first to a chloridizing roasting; the roasted ore is then
charged into tubs with false bottoms, and the cold solution of
salt and chlorine added. Silver ores from Arany-Idka, Hun-
gary, treated after this method, gave 98.94 per cent. of the
silver, all the copper, and nearly all the gold. An experiment
on five tons of ore gave a clear profit of seventy-five florins,
compared with amalgamation.
Roeszner roasts the ore with salt, extracts a part of the sil-
ver by Augustin's method with a hot solution of salt, and
treats the residue alternately with a solution of salt and chlo-
rine, and hot concentrated salt solution, for the extraction of
the gold and the remainder of the silver.
It is not absolutely necessary to roast the ore with salt, but
still preferable, especially if there is also copper in the ore,
*The solution must be cold.
18
258
CHLORINATION.
sufficient to be an object of extraction. There is a class of
silver ore found in considerable quantity in Nevada, which,
treated on a small scale with chlorinated salt solution, gives
nearly fifty per cent. of its silver, without roasting,—provided
it is ground very fine. The ore in question consists princi-
pally of argentiferous carbonates, containing copper, antimony
and lead. It has a greenish or black dull appearance, and is
generally rich in silver;-frequently occurring in Blind
Springs, Hot Creek, Humboldt, Lone Pine, and in Idaho.
There is also a light yellow earthy mineral in the form of
powder, a carbonate,-composed principally of antimony,
lead and silver, in Nevada, Arizona, etc. Also the Stedtfeld-
ite and Partzite (both, probably, the same mineral, and in
regard to origin, likely connected with the above named
carbonates). The last two minerals are greenish black, or
black, with a peculiar horny appearance, and also rich in
silver.
In treating these ores without roasting, besides the above
mentioned proportion of silver, copper also is obtained; but,
although in the working of the properly pulverized ore on a
large scale, a better result may be expected, than in the oper-
ating upon a few pounds only, a roasting or at least calcina-
tion, of the ore in question is advisable under all circum-
stances;-firstly, for the reason that, however carefully the
ore may be selected, a complete expulsion of the sulphurets
which accompany it can hardly be accomplished; and secondly,
on account of the difficulty of filtering a very finely pulver-
ized ore if not burned. But, as nearly fifty per cent. of the
silver can be extracted without roasting, it is reasonable to
expect that a short roasting will answer; and that a suitable
furnace may be capable of roasting about ten tous of the ore
per day, allowing thus a very economical treatment; and as
the copper contained in the ore is always worthy of consider-
ation, a few pounds of salt may be added before roasting.
This mode of extraction is very important for the new sil-
ver districts; not only because all the silver is obtained,
within a very small percentage, but because large quantities
CHLORINATION.
259
of copper are wasted by the present mode of silver amalga-
mation. This last named useful and valuable metal is in fact
looked upon with contempt, and considered to be worse than
sulphur or antimony, if combined with silver ores. It
appears, however, quite otherwise, if the lixiviating process.
is adopted, by which the copper is obtained separately with
an inconsiderable additional expense. The precipitating pro-
cesses, in most instances, will be found cheaper than the pan
amalgamation; and seem
and seem to be particularly suitable for
remote territories.
The precipitation of the metals obtained by the described
process, after leaching, can be effected in different ways. A
dilution of the salt leach with water, produces a white pre-
cipitate of chloride of silver. It takes about twelve hours for
all the silver to settle, and the fluid to become clear, ready
for the precipitation of the gold by sulphate of iron. After
this, the fluid, when clear, is conveyed into tanks containing
pieces of old wrought-iron, for the purpose of precipitating
the copper. This is the cheapest way of precipitation; but
the further reduction of the chloride of silver, by means
of zinc and sulphuric acid, is troublesome, and it might be
preferable to amalgamate the chloride with sodium-amalgam
and iron filings,—which, according to Professor Wurtz, is per-
formed almost instantly. Another inconvenience is the quan-
tity of water required for the precipitation of the chloride of
silver, amounting to about one-half of the volume of the lixi-
vium-thus diluting it too much for the copper precipitation.
Sulphuretted hydrogen, and polysulphide of sodium, pre-
cipitate silver, copper and lead together; it is therefore the
most proper way to precipitate the gold and silver in metal-
lic condition by metallic copper, and then both the dissolved
precipitating copper, and that from the ore, by means of old
iron.
..
2
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· TIE
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t
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Fig.1
5
4
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a
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19
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2
b
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1
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17
11
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20
日
​10
n
d
a
a
12
16
120
.
g
C
C
E
TO
f
K
C
21
gi
m
a
Tab. I.

о
22
f
112
Scale.
+=1 1'. Fus: 10.
+"' = 1'.
21... Fig 7,8,9,11,12,
1'..... Fig 1.
4 / 1. Ag: 13,14,
21.
1'..
Fig: 3 to b
1-1'... Fig: 15 to 22.
4
Fig 1
Б
LA
C
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b
n
m
6
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3
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18
9
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11
11
12
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it
α
b
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α
19
8.
b
C
j
17
Б
18
ས་
13
12
b
α
C
仁
​15
K n
f
с
·10
h
16
h
Q
阿
​h
Р
g
α
b
f
Tab. II.

α
Ꮵ
a
•
回
​ם
1
14
1
a
Scale
#
av loo
1.
Fig. 10
흉 ​오​..
100
F= 1.
Fig 1 to 4, 15 to 18.
4'-1'
Fig 12, 13
1.... Fig. 11, 8.
1- 1...... Fig. 6,7,14.
12- 1...
Fig. 5.
+
ა.
3
b
i
α
Fig 1
m
2
42.3.
K
日
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7
d
4
a
6
រ
2
b
5
α
14
7
30"
b'
1
-K
C
15
1038"
α
48-
'
17
α
d
b'
0.0
8
Во
A
45"
d
d
42″
7"
18
53"
37"
39"
16
26'
12"
b
X
d
b
α
10
•
11
entro
f
Tab. III.

e
121
9
12
M
$1
0/00
Scale
Fg: 12, 13,
Fig: 7, 14, to 18,
Fig: 1,2,3,8, 10, 11
1...
17- 1.
Fig: 4,5,6
13
а
eto
b
f
h
YPL
!
K
يد
g
*
फ
n'
2
e
a
+
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11
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d
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Fig. 1
m
12
..48"
.14" -->
36"
b
b
13
d
ig
OL
h
e
C
o
3
h
1
a
d
Ag
α
16"
4
26".
42
f
до
b
5
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22-
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g
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+
0
7
6
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C
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b
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ん
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17
8
201
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20
g'
at
en
f
1
1
K
#
11
19
9
+
9
A
14
d
15
८३
g
10
Tab. IV.


α
a
t
t 16
K
α
K
n
u
b..

• Scale.
B = 1'....Fig: 4
**= 1'………….. Fig: 5, 15,
....
요​....
- 1.....Mg: 1,2,3,6,7, 9 to 13,
=1.....Fig: 16,17,
f
----
力
​
18

Tangenta vân duendesha e madhe vet je van d
3'
6
i
L
323333 1932
D
୪
८
K
Fig: 1
v
QC
3
ية
V
m
LQ
1
De
q
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110
g
ML
m
ro
gi
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en
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i
VRYWHERE...
no
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P
g
L
m
5
5
4"
:
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m'
བའི་མཁག་ཕལག་མ་ཚང་མ་ས་ལ་ས་
K
8
11
h
표
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7
छू
ITALA
a
C
f
m
11211
INNA
112
E
n
""
R
n'
杰
​9
12"
n
口
​口
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مر
b
*
h
C
Z
A
窄
​e
୫
4'g
12
ㅁ
​σ
d
f
10. & of natural size
OL
کیا
h
口
​Tab. V.

Scale.
f'- 1'……………… .Fg: 1, 2
3″ - 1'. . . .
Fig: 7,8,9,12
4* = 1.... Fig. 4,
1호
​14-1'. . . . . . Fig: 5,
6,
4
n

Fig. 1
g'
3
१
१
4-1-
N
2
K
ร
10
x
J
A
B
3
પ
LO
5
D
om'
α
CAL
4
5
13
g
น
E
in'
૧
10
ex
*

10
น
૧
n
4'9
3.
7
4
m
K
m
क
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Im
५
g
8
1%
In
ん
​#1203
6
f
α
10
૫
ی
B
е
か
​m
N
Tab. VI
પ
10
१
10
り
​น
e
か
​OL
M
N
b
K
B
11
12
q
ww
回
​ง
9
་
A
6
B
x
α
10
x0
-1
+7 = 1.
Scale.
Rg: 7,12
Fig: 1,2,5,6,10,11
α
2
مدامات
Mig: 8.



ດ
1000000
1000000
a
B
Ъ
Fig. 1.
"
b
2
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19
3
4
14
D
13
d
16
b
15
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g
K
1
Config
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b
❤
d
α
C
11
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7
OL
39'4"
FOTO
e
12
9
d
18
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17
•
+
1
α
OL
b
C
C
b
10.
୧
a
0
0
ď
8
9
ما
Th
с
h
30'
రా
α
d
сл
h
PO
6.
12'
20"
in
201
日
​„8,01
Tab. VII

ď
12
12
20"
Scale.
-1
3
16
-1
Fig. 7,8,9.
Fg5,6
G
T... Fig: 11 to15,17
1=1……….. Fig: 16
f
#=1'.... . Fig: 1,2
=-1..
Fig: 18.
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