IMAGE EVALUATION
TEST TARGET (MT-3)

1.0

I.I

■^1^ 125

■ 50 ■'

ima

|j6

2.2

S 1^ iio

IL25 llllljy_ ill 1.6

:<\^

<!!^. *:

"V I " I'l^ 1

CIHM/ICMH

Microfiche

Series.

CIHIVI/ICMH
Collection de
microfiches.

Canadian Institute for Historical Microreproductions Institut Canadian de microreproductions historiques

1980

Technical Notes / Notes techniques

The Institute has attempted to obtain the best
original copy available for filming. Physical
features of this copy which may alter any of the
images in the reproduction are checked below.

Coloured covers/
Couvertures de couleur

L'Institut a microfilm6 le meilleur exemplaire
qu'il lui a 4t6 possible de se procurer. Certains
d6fauts susceptibles de nuire A la quality de la
reproduction sont notis ci-dessous.

Coloured pages/
Pages de couleur

P<
of
fil

Tl
cc
or

D
D
D

Coloured maps/

Cartes giographiques en couleur

Pages discoloured, stained or foxed/
Pages ddcolories. tachet6es ou piquAes

Tight binding (may cause shadows or
distortion nlong interior margin)/
Reliure seird (peut causer de I'ombre ou
de la distortion le long de la marge
intdrieuni)

D
D

Coloured plates/
Planches en couleur

Show through/
Transparence

Pages damaged/
Pages endommag^es

Tl
fil
in

M
in

uf
b(
fo

Additional comments/
Commentaires suppidmentaires

Bibliographic Notes / Notes bibliographiques

D
D

Only edition available/
Seule Edition disponible

Bound with other material/
Relid avec d'autres documents

Pagination incorrect/
Erreurs de pagination

Pages missing/
Des pages manquent

Cover title missing/

Le titre de couverture manque

IVIaps missing/

Des cartes g6ographiques manquent

D
D

Plates missing/

Des planches manquent

Additional comments/
Commentaires suppi^mentaires

The images appearing here are the best quality
possible considering the condition and legibility
of the original copy and in keeping with the
filming contract specifications.

Les images suivantes ont 6t4 reproduites avec le
plus grand soin. compte tenu de la condition at
de la nettetA de rexemplaire film*, et en
conformity avec les conditions du contrat de
filmage.

The last recorded frame on each microfiche shall
contain the symbol ^^> (meaning CONTINUED"),
or the symbol y (meaning "END"), whichever
applies.

Un des symboles suivants apparattra sur la der-
nlAre image de cheque microfiche, selon le cas:
le symbole — ^ signifie "A SUIVRE", le symbols
▼ signifie "FIN".

The original copy was borrowed from, and
filmed with, the Itind consent of the following
institution:

Canadian institute for Scientific and
Technical Information, National
Research Council

Maps or plates too large to be entirely included
in one exposure are filmed beginning in the
upper left hand corner, left to right and top to
bottom, as many frames as required. The
following diagrams illustrate the method:

L'exemplaire film6 fut reproduit grAce d la
g6nArosit6 de l'6tablissement prAteur

Institut Canadian de I'information scientifique
et technique, Conseil national des recherches

Les cartes ou les planches trop grandes pour Atre
reproduites en un seul clichA sont filmAes A
partir de I'angle supArieure gauche, de gauche A
droite et de haut en has, en prenant le nombre
d'images nAcessaire. Le diagramme suivant
illustre la mAthode :

I'lC

pra(;ttcal instructions

FOR V H K 1),K r K R M I X A '1' 1 () N
BY FURNACl-: ASSAY

GOLD AND SILVER

I N ROC KS Ax\ 1) OR KS,

K. J. CHA1^NL\N,

I'u.l)., 1.1,1).

'rofessur of Miiieraloyy and (leology in University Colioge, loioiUu ; ;uirl
Ai-ting Prolessor of Mining Geology, Blowpipe Practice, and
Assaying, in the l\)ronto School ot" Practical Science.

I'O KON TO :
COl'l'. CI.AKK .V CO., 9 FRONT STKi:!.'! WK.-^r

i88i.

AOT1.IV "'»

CHAPMAN'S

ASSAY NOTES.

INSTRUCTIONS

FOR THK I)ETP:RMINATI0N OF (iOFl) AND
SILVER IN ROCKS AM) ORES.

RV I UK SA\fh: AUTHOR.
I.

AN OUTLINM-: OF THE GEOLOC.V OK CANADA.

H\SKI) ON A SUBDIVISION OF THK PKOVINCKS
INTO NATURAL AREAS.

/r/M su- sketch-maps and 86 fi^ires of charaderhtir fossils.

Thi-, is the only published work which presents a systematic view
ot the geology of the entire Dominion. It ha-, been drawn up not
to serve simply as a College text-book, but for consultation by
goneral readers.

II.

HLOWl'llM-: PKAC'l'K K.

WIIH oRKilNAl. L'ABLES FOR THE UETERMIN A Ih 'N Ol-
AI.I. KNOWN MINERALS.

rhis work (published in 1880) comprises two distinct parts : An
Cnitline of tilowpipe Practice, as applied to the qualitative examma-
t,on of inorganic bodies generally ; and a series of Determmatu.-
Mineral Tables, with accompanying crystallographic an.l spectn,-
.'icopic notes.

COPl', Cl.AKK & CO., rORON TO.

ADVERTISEMENT.

The following notes contain definite instructions for the
examination or assay by furnace operations of all rock-mat-
ters and other naturally occurring mineral bodies in which
gold or silver is known or suspected to be present. Although
given expressly in condensed form, the notes embody various
tables and many explanatory directions not given, to the
writer's knowledge, in other publications ; whilst, at the
same time, they are kept free from sundry complicated de-
tails belonging solely to the assay of bullion and other arti-
ficial alloys. As they are intended for actual use in the
laboratory, it has not been thought necessary to add figures
of the balances, furnaces, muffles, scorifiers, tongs, cupel-
moulds, and other pieces of apparatus employed in these
operations. The student will necessarily see these things
for himself ; and he will find their proper form and manipu-
lation fully described in the text.

School of Practical Science, Toronto,
May 30th, 1881.

CONTENTS.

— • —

CHAPTER I.

INTRODUCTORY OBSERVATIONS.

§ 1. Assays in general. Rock and Mineral assays for Gold and

Silver "

§ 2. Gold ores **

§ 3. Silver ores **

CHAPTER II.

SAMPLING AND PREPARATION OF ASSAY-MATTERS.

§ 1. Assay-Samples in general • 1^

§2. Preparation of the assay -matter : Implements required . . U

CHAPTER III.

THE SCORIFICATION PROCESS.

§ 1. Object and general explanation of the Process 14

§ 2, Apparatus -^^

§ 3. Reagents • ^^

§ 4. Weighing and dressing samples for scorification 18

§ 5. Examples of assay-mixtures 20

§ 6. Details of the Scorification Process • 24

§ 7. Separation and cleaning up of the workable lead or scori-

fication-button 25

CHAPTER IV.

THE CRUCIBLE PROCESS.

§ 1. Object and general explanation of the Process 26

§ 2. Apparatus 27

§ 3. Reagents ^^

CONTENTS.

§ 4. Roasting 32

§ 5. Weighing and dressing samples for crucible assay 33

§ 6. Furnace manipulation 35

§ 7 Manipulation of the Crucible Button 36

CHAPTER V.

CUPELLATION.

§ 1. Object and essential character of Cupellation 37

§ 2. Apparatus and api^liances . 38

§ 3. Preparation of Cupels 40

§ 4. Details of the Cupellation Process 43

CHAPTER VI.

ESTIMATION OF GOLD AND SILVER IN CUPEL BUTTONS.

§ 1. Explanatory Remarks on the Separation of Gold and

Silver 48

§ 2. Apparatus 50

§ 3. Reagents 52

§ 4. Details of the Process 52

CHAPTER VII.

ASSAY TABLES.

Table I. Assay-weight, 5 grammes 57

Table II. Assay-weight, 25 grammes 5^

Table III. Assay-weight, 50 grammes 59

Table IV. Assay- weight, 29*17 grammes CO

Table V. Assay- weight, 32 67 grammes 60

Table VI. Assay-weight, 1 oz 61

Table VII. Percentage Values 62

Table VIII. Average value of Gold 63

Table IX. Approximate Sp. Gr. of Gold Alloys 63

*•

FURNACE ASSAYS

GOLD AND SILVER ORES.

CHAPTER I.

Introductory Observations,

[Nature of Assays. Enumeration of Processes.

Ores.]

Gold and

§ 1. Assays in general. Rock and Mineral Assays for
Gold and Silver : — Assaying is strictly a bnmcli of quanti-
tative chemical analysis, diiftjring from the latter, properly
so-called, by determining only those components of a sub-
stance which impart to it a commercial value. In some
cases, the assay is ])erformed by furnace operations ; in
others, by solution and precipitation, &c., as in ordinary
chemical analysis ; and in others, again, by volumetric
methods. The present Notes refer solely to furnace
assays of mineral matters containing, or suspected to
contain, gold or silver.* These assays, as regards their
modus operandi, are of two general kinds : Scorification

* Mining Assays of this description are quite distinct, it must be understo(,d,
from Mint or jeweller's assays, in which bullion and metallic alloys containing
gold and silver alone come under examination. The assays to which the pre-
sent publication refers are not gold and silver assays, properly so-called, but
assays of rocks,vin6stones, and mineral ores generally, for the detection and
determination of any gold or silver that may be present in these matters.

8 FURNACE ASSAYS.

Aasays, applied to comparatively rich ores; and Crucible
Assays, adopted essentially in the examination of poor
ores. In both, however, the preparatory stages (including
the sampling and preparation of the assay-matter) are
alike ; and both terminate in the common process of
Cupellation. In the scorification assay a small portion,
only, of the prepared ore is directly operated on ; whilst
in the crucible assay a much larger portion of the ore can
be taken. In all cases, at least a couple of assays should
be made simultaneously.* The complete assay comprises
the following processes :
(1) Sampling and Preparation of the Assay-matter (Chapter II.)

! Scorification (Chapter III.),
or
Crucible Treatment (Chapter IV.)

(3) Cupellation (Chapter V.)

(4) Treatment of the Cupel-Button (Chapter VI.)

* Objections are often ignorantly urged against laboratory assays, as being
made on portions of matter too small to give trustworthy results regarding the
quality of the vein or other deposit to which the assays refer ; but if the
samples be properly taken (as directed in Chapter II), assays of even a few
grammes of matter (forming in most cases, it must be remembered, portions of
samples weighing several pounds) may be thoroughly relied on as regards the
general cliaracter of the deposit— i. e., its comparative richness or poverty —
although this may of course vary at different depths. Very frequently an assay
of this kind serves to reveal the absolute barrenness of deposits from which
large returns are falsely stated to have been obtained ; and much subsequent
loss and disappointment is thus prevented. In preliminary mining operations,
again, small assays are especially useful ; and when the ore is not of an ex-
ceedingly variable character their results are quite as trustworthy as those
derived from the treatment of large quantities of the deposit. This wiU
apply especially to argentiferous lead-ores and auriferous pyrites. Assays,
also, are indispensable in checking the results of furnace operations on the
large scale ; and in the purchase and sale of ores generally.

^ [«

GOLD AKD SILVER OllES.

§ 2. Gold Ores : — The metal gold occurs in Nature
chiefly under the following conditions: (1) as ''free
gold " (i. e., in a simple, uncombined state, although com-
monly alloyed with a little silver) disseminated either in
small nuggets or in more or less imperceptible particles
through quartz or other solid rock-matter; (2) in the
same condition in river-sands and gravels or other
alluvial matters forming the "jjlacer digginrjs,'' &c., of
Western explorers, the " Sei/enlager" of Germsin miners;
(3) in probably the metallic state (or as an arsenide or
sulphide?) in some examples of mispickel, iron pyrites,
copper pyrites, blende and other similar ores, in which
it is present in very minute quantity as an " accidental
component;" and (4), in some rare tellurides. Assay-
samples consist very generally of pieces of quartzose
gangue or veinstone, carrying interspersed particles of
pyrites, mispickel, zinc-blende, galena, &c., without any
visible show of gold.

§ 3. Silver Ores: — These are somewhat numerous.
The principal comprise: (1) Native silver (usually in
small grains or scales, or in leafy or filiform examples) in
<i[uartzose or calcareous gangues; (2) Silver Glance (Ag ^ S
with 87 per cent silver, usually in black, malleable, leafy
masses or small crystals); (3) Red silver ores (the dark-
red consisting of S 17.7, Sb 22.5, Ag 59.8, the light-red
of S 19.4, As 15.2, Ag 65.4 : both distinguished by their
red streak and blowpipe reactions); (4) Horn-silver ore
(chloride of silver with 75.3 per cent metal) ; and (5)
argentiferous varieties of Galena, Grey Copper Ore, and

10 FURNACE ASSAYS.

other sulphides. Assay. samples consist very commonly
of galena (more or less pure), or of associated native
silver, silver. glance, argentiferous galena, blende, pyrites,
<fec., in a mixed gangue of quartz and calcite, or calcite
and heavy spar. As regards galena, the structure of the
mineral is no criterion of the silver-percontage. In some
mines the fine-grained varieties are the xnore highly ar-
gentiferous ; but, in others, the coarsely-crystalline ex-
amples yield the largest amount of silver. Wliere the
amount reaches one per cent., it invariably arises from
intermixed native silver or silver-glance. Kich examples
of galena shew very frequently in places a peculiar purpk
tarnish.

CHAPTER II.

Sampling and Preparation of Assay-Matters.

[Selection of Samples. Preparation of Ore for Assay : Crushing^
Sieving, &c. ; Apparatus required.]

§ 1. Assay Samjyles : — It happens very commonly that
the assayer has no hand in the selection of the samples
sent to him for assay, in which case the sender is, of
course, alone responsible for the accuracy of the assay
results as applied to the deposit generally from which the
samples were obtained. But in some cases, the assayer,
t^specially if competent to report on mineral locations,
selects the samples personally, or is able to give direc-
tions for their proper selection. Unless the sample be
fairly chosen, the assay-results as a rule are not only of

SAMPLING OF ORES.

little value, but are often absolutely mischievous in con-
veying to the public an erroneous impression of the ore.
Mineral properties have frequently been grossly exagge-
rated in value by the assay of unfairly selected samples ;
whilst in other instances they have been unduly depreci-
ated from the same cause. In the selection of a sample,
a number of small pieces should be taken (by the pick or
hammer, or by properly placed shots) from various parts
of the deposit, and from each of these, smaller fragments
may be broken for final reduction to powder in the mor
tar. A sample consisting of a single piece of ore, how-
ever large, is practically of little value. As to the amount
to be taken, much must of course be left to the judg-
ment of the collector ; but ten or twelve pounds, in
quarter or half pound pieces, taken from as many
different spots as possible, will in general be sufficient.
In deposits of comparatively uniform character less will
be required than in other cases. Two or three small
pieces of galena, for instance, will be sufficient to show
if the lead carry a workable amount of silver ; but in
sinking on a galena vein, the ore should be tested at
difierent levels, and also at different spots during the
extension of the drifts.

§2. Preparation of the Assay-matter ; Implements re-
quired : — Before commencing operations in this and
other cases, the student should arrange on the work-
bench or table, before him, the various implements
(apart, of course, from balances, furnaces, anvil, and

» I

12 FURNACE ASSAYS.

other larger pieces of apparatus) required in the opera-
tion immediately under hand ; and, after use, each piece
should be carefully wiped with a soft cloth, and returned
to its proper place in the laboratory. In the jjreparation
of the assay-matter, the following articles are required :
a strong hammer, with head of about 1 lb. weight ; an
iron pestle and mortar ; a painter's brush ; a sieve with
metal bottom ; two large sheets of paper ; a large porce-
lain capsule or other vessel to hold the powdered ore.
These are described below.

The portion of the sample finally selected for assay
must be reduced to a fine powder in an iron mortar
furnished with heavy pestle ; and care must be taken that
the whole of this portion of the sample be so treated. If
the harder parts, after a few poundings, be discarded, the
assay is certain to be either richer or poorer than the
proper average. Assistants frequently shirk the labour
of pounding, after a certain bulk of pounded matter is
obtained. But the easily pounded portions in the case
of soft ores in quartz or other hard gangue will
necessarily give too rich an average, whilst in other
cases, as when the gangue consists of calcite or of more
or less decomposed rock-matter, the assay will be too poor
to fairly represent the sample. The whole of the selected
portion of the sample must be reduced to powder in small
pieces at a time.

The disintegration of very hard samples may be
facilitated by first " astonishing " the larger pieces of
rock. This is effected by heating them strongly in a

'■

■

PREPARATION OF ASSAY-MATTRRS.

la*

furnace (or in an ordinary stove or fire, or in a crucible
over a large Bunscn burner), and ther dropping them into
water. After this, when thoroughly dried, they are
easily Ijroken up.

In pounding, the pestle is brought down by repeated
blows upon the ore, grinding being avoided in order to
avoid abrasion of the mortar. A. convenient size of'
mortar is one of about eight inches diameter at the top,
and eight or ten inches in depth ; but it is desirable to
have in the laboratory an additional mortar of some-
what larger size, and another of smaller dimensions.
Between the separate poundings the ore is emptied out
of the mortar on to a sheet of paper, and from this into a
a sieve over another sheet of paper. The sieve may
have a diameter of about six inches, and depth of four
inches, with wooden rim and bottom of fine iron or brass
trellis with about thirty meshes to the square inch. It
is convenient to keep at hand a cylindrical brush (such
as painters use) with which to sweep out the finer portion
of the powdered ore, as this often adheres to the sides of
the mortar. After passing through the sieve, the powder
should be poured into a large porcelain capsule or other
suitable receptacle, and a label should be attached at
once by a drop of mucilage to the side of the vessel. A
precaution of this kind is especially necessary where
several assays are being made at one time. It is also-
advisable to preserve the powdered sample, thus labelled,.
for a time, in case a repetition of the assay shouM be*,
necessary.

14 FURNACE ASSAYS.

CHAPTER III.

The Scorification Process.

[Object of the Process. Apparatus and Reagents. Details of
Process. Tables of Assay-Mixtures.']

§1. Object and general explanation of the Process: —
The process of scorification has for its direct object the
combination of all the gold and silver, present in the >•

assay-matter, with pure lead (from which these metals
are afterwards separated by cupellation, Chapter Y.);
whilst iron, arsenic, sulphur, intermixed rock-matter,
&c,, become "scorified" or pass into slag. The process is
performed in small, thick, saucer-shaped vessels of fire-
clay, known as " scorifiers." These are strongly heated
in a muffle or thin fireclay oven according to the method
described in detail under § 5, below, and the "workable
lead" is then poured into an iron or copper mould,
previously warmed to prevent the lead from spitting or
throwing off small portions of its mass. The lead button
thus obtained, is squared up and cleaned from adherent
slag on the anvil, after which it is cupelled as described
in Chapter V.

§ 2. Apparatus : — The following pieces of apparatus
are needed in preparing the assay-mixture and carrying
out the process of scorification. ( 1 ) An ordinary chemical-
balance, with gramme weights ranging from fifty

■

SCOIIIFICATION APPAllATL'S.

grammes downwards. f (2) A porcelain capsule or
crucible to liold the weighed matter, and a tare for these
vessels. The tare may consist of a thin brass box with
sere wed-on top, holding a few particles of test-lead or
some fine shot. (3) A small copper-scoop, or two, for
taking up the powdered ore, test-lead, (fee, and a small
spatula for mixing the assay-matters. (4) A fixed or
portable muflle-furnace. For ordinary work, a small
portable furnace is amply sufficient. The square fire-
clay furnaces, bound with sheet-iron bands, made at the
Battersea Works (London, England,) are especially
serviceal)le. The cracks, which commonly occur in
them when they are first lighted, are of no consequence.
A convenient size is that denoted by the letter C,
stamped on the moveable doors and other pieces of the
furnace. This size takes a muffle 8 inches long by 4J
inches broad. The small "Luhme furnaces," made of
sheet-iron thickly lined with fire-clay, are also very
useful ; but the fire-clay lining will require to be patched
or replaced pretty constantly if the furnace be in active
use. Repairs are effected by kneading some good fire-
clay with a very small quantity of water into a stiff* paste,
and pressing this strongly into the damaged places by a
trowel, the surface being properly smoothed over after-
wards. The patchings must be left to dry thoroughly

t A very expensive balance is not required in these preliminary assaying
processes, but for weighing the cupellation buttons and the fine gold separated
from the latter, a delicate assay-balance is, of course, essential (see Cliapter
VI.). For crucible operations it is convenient to have certain special weight s ,
as described under the crucible process in Chapter IV.

16 FURNACE ASSAYS.

for several days before the furnace is again used.* The
fuel for these furnaces consists of charcoal chopped
by a small light hatchet into blocks of about two inches
square. Large pieces do not fall properly, and dust
destroys the draught. (5) A fire-clay muffle of suitable
dimensions to fit the furnace. Formerly, these muffles
had always slits or air-jmssages at the sides and back,
but they are now generally made without am, and are
consequently stronger. Under both forms, however,
they are easily broken. Duplicates should, therefore, be
kept at liand.t It is advisabe to spread a little boneash
thinly over their floor to prevent the scorifiers from
adhering in case some of the contents of the latter should
be allowed by mismanagement to overflow, or should
escape through the cracking of a faulty scorifier. (6)
An assortment of fire-clay scorifiers. Those turned out
by the Battersea Works are of excellent quality. The

* Fur private laboratories, or occasional use, the small gas-furnaces maJe
by Fletcher and others, if properly handled, are also very serviceable.

t Fire-clay muflfles, in remote places, cannot always be procured. The writer
has thus been compelled at times to use cast iron muffles. In these, a slit at
the back can of course be made in the casting ; but if holes at the side be re-
quired, they must be bored subsequently. Muffles of this kind answer well
enough in small furnaces ; and, as a rule, they will serve for thirty or forty
assays before becoming too much corroded for additional use. In wind-fur-
naces, however, or where the draught is very strong, they are rapidly melted
and destroyed. Wrought iron muffles, made in two pieces, answer better. In
these, the floor has a slight flange turned up on each side, and the dome con-
sists of a separate piece, bent into the form of an arch and kept by the flanges
in its place. The back is entirely open, but it can of course be closed or par-
tially closed by a piece of fire-brick roughly cut into shape. A large cruciblet |

laid on its side, may sometimes serve as a makeshift muffle where nothing else
is at hand. In the small gas-furnaces, plumbago mufflss are commonly used.

SCORIFICATION APPARATUS.

more generally useful sizes measure two inches, and an
inch-and-three-quarters, respectively, across the top.
(7) A pair of tongs, about two feet in length, with spring
blades flattened and somewhat enlarged at the ends, for
feeding the furnace with charcoal. These are commonly
known as furnace-tongs or charcoal-tongs. (8) A pair
of scorifier-tongs for placing the scorifiers in the muffle,
and for removing them from the latter, after scorifica-
tion, and pouring their contents into the assay-mould
described below. These tongs have flat spring blades of
about three feet in length. One is the under and the
other the upper blade. The under blade is fashioned
into a kind of fork or horseshoe-shaped expansion to fit
the bottom of the scorifier. The upper blade is of one
width throughout. When in use it goes across the flat
top of the scorifier, and as the base of the latter rests
within the horseshoe of the lower blade, the scorifier is
held very securely, both when placed in the muffle and
when removed and reversed over the assay-mould. (9) A
thick slab of iron or copper, with two (or several) saucer-
shaped depressions on one of its flat surfaces, and a metal
handle (with wooden " grasp ") strongly screwed into one
end. This is the assay-mould for the reception of the
"workable lead" from the scorifier. The bottom of the
saucer-shaped receptacles must be rubbed lightly with
chalk or red ochre to prevent the lead from adhering,
and the entire mould must be warmed strongly imme-
diately before use. This is best effected by placing it for
a few minutes on the ledge before the muffle door, or on

tS FURNACE ASSAYS.

the outside of the furnace at the top. (10) An anvil or
block of hard steel from four to six inches square and of
about the same thickness, with a tongue or projection
several inches in length at the under side for insertion
into a block of hard wood. The latter may consist of
part of a tree-trunk eight or nine inches or a foot in
diameter and about 2J or 3 feet high. It should be
perfectly level at the base so as to stand firmly and
securely. A good hammer, with head of about 1 lb. or
1^ lb. in weight, should accompany the anvil, and be hung
up (between a couple of nails supporting the head) on the
adjacent wall. One end of the hammer-head must be
chisel-shaped, the other end flat and square.

§ 3. Reagents : — The reagents required in the scorifica-
tion -process comprise merely granulated lead (commonly
known as " test-lead "), dried borax, and (for occasional
use) a little charcoal powder. Every sample of lead
purchased for the laboratory should be tested by cupella-
tion before actual use, to ensure the absence of silver.
See Chapter V.

§ 4. Weighing and Dressing of Samples for Scorif ca-
tion: — The sieved and thoroughly mixed powder {§2,
Chapter II.) is poured from its receptacle on to a sheet
of paper and is made up into a conical heap. This is
divided roughly by a spatula into quarters, and from
each quarter small portions are taken and placed in the
weighing capsule until 5 grammes are thus weighed out
for assay. This amount is placed in a scorifier, and is

8C0RIFICATI0N MIXTUUES.

191

dressed with its proper amount of granuliitc 1 kfud, vary-
ing from about 20 to over 50 grammes, accoi-dincf to the
nature of the substance, as shewn in the Tables of Assay
mixtures under § 5, below. About one-third, or rather
more, of the lead, is mixed in the scoritier with the
powdere<l ore, and the rest is spread over the surface of
the mixture, — a small amount of dried borax (usuall}
about a gramme : sec the Tables) being finally strewed
over the whole. The lead, to save time where many
assays are being made, may be mejisured instead of being
weighed, as a gramme more or less is of no moment ; and
the amount of borax, after a little practice, may be
estimated with sufficient accuracy by the eye. A lead-
measure may be made by marking off with a fde on a
sto'.it test-tube the spaces occupied respectively by
weighed quantities of lead, as 20, 30, 40, 60, 80 and 100
grammes.

A couple of scorifiers should in all cases be dressed in
this manner for each assay ; and it is often advisable to-
operate on an additional quantity of the ore, if the muffle
will accommodate a larger number of scorifiers. Ordinary
muffles will take four or even six. As a rule, however,,
if the assay-matter be reduced in the mortar to a very
fine powder, and the particles of this be intimately
mixed, a couple of scorifications will give the same^
average as half-a-dozen. The weight of ore taken for
assay is, of course, more or less arbitrary ; but the
amount recommended, five grammes for each scorifier, is-
about the maximum that can be safely used.

20 FURNACE ASSAYS.

§5. Examples of Assay-mixtures: — The following
mixtures will meet cases of general occurrence. In inter-
mediate cases, the operator must use his own judgment
as to the proper amount of lead required. It is always
better to use too much than too little. With too small
a quantity, the scorification is incomplete, and the lead
button does not separate properly from the slag, or is
brittle from retention of sulphur, arsenic, ifec, (see under
the description of the process in § 6). But with too much
lead, on the other hand, an inconveniently large button
for cupellation is obtained, and the operation occupies
more time. As a rule, assay-matters containing nickel,
copper, or arsenic, require a largo quantity of lead for
proper scorification ; whilst quartzoso and other rock-
matters sparingly interspersed with pyrites, or other
metallic particles, require comparatively little : practice
soon suggests the proper quantity. Witli siliceous
gangues, very little borax is wanted (unless much nickel,
arsenic, copper, or iron be present). A gramme is about
the average quantity required. With so-called " basic "
gangues, on the other hand, that is, when the veinstone
or rock-matter is essentially calcareous or barytic, or
when the assay-matter consists largely of brown iron ore
arising from decomposed pyrites, somewhat more must be
used. If too much be taken, however, it is apt to impede
the scorification, by covering the metallic bath with a
thick coating of fused glass, and so preventing the access
of air. Where much, therefore, is needed, it is better to
strew a portion, only, over the assay mixture at first, and

SCORIFICATION MIXTURES.

to add the remainder towards the close of the operation.
It may be folded in a piece of screwed-up tissue-paper,
and placed in this manner by the furnace-tongs on the top
of the crust or slag. Occasionally, also, it is advisable
to add a little powdered charcoal in the same manner.

(1) Quartzose, granitic, gneissoid, or other essentially
siliceous rock-mattei*s with sparingly interspersed metallic
particles (i. e., specks of pyrites, galena, &c.):

5 grms. ore.
25 to 30 grms. lead,
^ grm. borax.

(2) Quartzose or other siliceous rock-matters with
thickly disseminated pyrites :

5 grms. ore.
35 to 40 grms. lead,
f to 1 gram, borax,

(3) Iron Pyrites in quartzose gangue :

5 grms. ore.
45 to 50 grms, lead.
I to 1 grm. borax.

(4) Copper Pyrites, or intermixed Copper and Iron

Pyrites, in quartzose gangue :

5 grms. ore.

60 to 70 grms. lead.
1 grm. borax.

(5) Intermixed Iron Pyrites, Copper Pyrites and Blende
in quartzose, or mixed quartzose and calcaieous gangue :

6 grms. ore.*

60 to 70 grms. lead,
1| to 2 grams, borax.

* Take half-weights, or divide into two portions, unless very strong heat can
be got up. The greater part of the borax should be added to the crust or
slag, at the end of the second stage of the process : see § 6.

22 FURNACE ASSAYS.

(6) Arsenical Pyrites in quartzose or calcareo-quartz-
ose gangue.

5 grms. ore.*
80 grms. of lead.

2 to 3 grms. borax.

(7) Nickel-holding, arsenical, sulphurized ores in
quartzose or calcareo-quartzose gangue.

5 grms. ore.*
80 to 100 grms. lead.
5 grms. borax.

(With ores of this character it is often necessary to repeat the
Bcorification).

(8) Arsenical or Antimonial lead or copper ores, or
mixture of these, in calcareous or quartzose-calcareoua
gangue :

5 grms. ore.*
100 grms. lead.

3 to 3^ grms. borax.

(With these ores, also, it is often necessary to repeat the
Bcorification ; and, as a rule, the assay mixture should be scorified
in two or three separate portions. )

(9) Intermixed Blende and Galena (or Blende, Galena,
and Iron Pyrites) in essentially calcareous or barytic
gangue.

6 grms. ore.

40 tu CO grms. lead, t
2 to 3 borax.

* See preceding foot-note.

t If the Blende greatly preponderate, 55 or 60 grammes of lead must be taken,
or in some cases as much as 80 grammes.

SCORIPICATION MIXTURES.

(10) Pyritous Galena (or mixtures of pyritous galena
with Native Silver and Silver Glance.)

5 grms, ore.
35 to 40 grms. lead.
1 grm. borax.

(11) Galena (oi intermixed galena, Native Silver and
Silver Glance) free or practically free from pyrites and

blende.

5 grms. ore.
25 to 30 grms. lead,
f to 1 grm. borax.

'\2) Native Gold or Native Silver in visible particles

in quartz or other rock-matter.

5 grms. ore.
. 40 to 50 grms. lead.
1 grm. borax.

Care must be taken in cleaning up the workable lead-button
on the anvil, as the presence of gold may render it more or less
brittle.

(13) Native Gold or Native Silver mixed with copper-
pyrites, or other copper ores, in quartzose or other

gangue.

5 grms. ore,
65 to 60 grms. lead.
1 ^ grm. borax.

If Native Copper, or much copper ore be present, 80 to 90
grammes of lead must be taken.

(14) Silver Glance or other Rich Silver minerals, or
mixtures of Native Silver with argentiferous galena, (fee

5 grms. ore.
35 to 40 grms. lead,
j^ to 1 grm. borax.

^11

24 FURNACE ASSAYS.

§ 6. Details of the Scorification Process : — This process
includes three stages : the fusion stage ; the oxidation, or
scorification stage, proper; and the coup-de grace or final
stage.

(1) The fusion stage: — The scorifiers containing the
dressed ore (as described under § 4) are taken separately
by the forked tongs (§ 2 (7) ) and are placed in the glow-
ing muffle.* A few hot coals are heaped about the
opening of this, and the door is ra[)idly closed. Com-
plete fusion of the assay-mixture is thus soon clTected,
but the muffle door is kept closed for from 20 to 30
minutes. In ordinary cases, a period of 20 minutes is
sufficient for this stage of the scorification process.

(2) The oocidation or slagging stage : — The muffle door
is now opened, and the hot coals are removed from its
mouth. A current of air is thus carried over the scori-
fiers, by which sulphur, arsenic, and other volatile
matters, if present, become eliminated ; and intermixed
rock-matters, iron, &c., pass into slag or scum. In this
manner, the surface of the fused bath becomes gradually
covered or partially covered with an infusible crust, when
the operation is completed. The time necessary to effect
this, varies from about 25 to 35 minutes. If several
scorifiers be in the muffle, those nearest the opening may

* The furnace should bo lighted and well filled with charcoal about half-an-
hour before required for use ; and, during operations, the heat must be main-
tained by the addition of a few pieces of charcoal from time to time. Begin-
ners often fail in their work (more especially, perhaps, in the cupellation
process) by neglecting to keep the furnace properly fed.

SCOniFlCATloN PHOCKRS.

or,

have a hot coal placed against them to ke(3j) up the heat ;
but otherwise it is better to let the air have full access by
removing all the hot coals when the door is withdrawn
at the commencement of this second stage.

(3) Final or Coup-de-grace stage : — In this stage, the
muffle-door is again closed, and a good heat is kept up for
five or six minutes, the object being to cause a complete
precipitation or separation of the workable lead from the
infusible scum.

§ 7. Separation ami cleariing up of the workable lead : —
The seorifi cation process finished, as described in the pre-
ceding section, and the iron or copper mould (previously
heated, § 2 [Uj ) being placed conveniently on a flat stono
or on the brick floor in front of the operator, tlie mnfiii^
door is opened, and each scorifier is seized carefully by
the foi'ked tongs (§ 2 [S] ), and its fluid contents are
poured into one of the cavities of the mould. This
should be done rapidly, but without undue haste, by a
continuous turn of the wrist, until the scorifier is com-
pletely reversed over the mould. It is then tapped gently
against the edge of the cavity, and laid aside. The lead!
generally forms a flat cake or disc in the centre of the
cavity, surrounded by a vitreous, brittle slag ; and it is
easily removed, after standing to cool for a few minutes,
if the surface of the cavity has been previously rubbed
with chalk or ochre as directed under § 2. The lead
disc or button is then taken to the anvil and carefully
freed from adhering portions of slag under the hammer.

FURNACE ASSAYS.

It should not, however, be beaten out too thin, but should
be worked square by gentle blows on the edges, and the
comers should be slightly rounded in order to prevent
abrasion of the cupel in the after process of ciipellation
(Chapter V.). A so-called "scratch brush," made of
iron wire, is sometimes used to clean the surface of the
button more thoroughly, but this is rarely necessary.
The lead-button should be soft and malleable. If brittle,
the scorification will not have been properly conducted
or sufficiently prolonged. In this case the button must
be re-scorified with the addition of 15 or 20 grammes of
test-lead and a little borax.

II
ii

CHAPTER IV.

The Crucible Process.
[Object of the Process. Apparatus aud Reagents. Manipulatio7i.]
§ 1. Object and general explanation of the Crucible
process : — In the case of very poor ores, or in the exam-
ination of rock-samples merely suspected to contain traces
of metal, the scorification process, described in the pre-
ceding Chapter, cannot conveniently be employed, as only
a small amount of material is capable of being assayed at
a time by that method. Where, for instance, a substance
contains merely a few dwts. per ton of gold or silver, the
workable lead obtained from five grammes of ore neces-
sarily yields on the cupel a scarcely appreciable amount
of metal. Several scorification lead-buttons might of
course be obtained, but the large amount of lead to be

APPARATUS.

•

got rid of would then become exceedingly Inconvenient.
In cases of this kind, therefore, a crucible fusion should
be resorted to, by which 25 or 50 grammes of the sieved
ore — or even more, if thought desirable — may be operjited
upon at one time. The ore (after previous roasting, if
necessary, as desciibed in detail under § 5 of this Chapter)
is fused in a fire-clay crucible with its own weight, or
rather more, of litharge, and three or four times its weight
of a mixture of carb. soda and borax or other suitable
flux (see § 3). The litliarge becomes reduced to metallii-
lead. This takes up all the gold and silver (togethei-
with copper, &,c.) that may be in the ore, and sinks down
to the bottom of the })ot, where it forms a workable
button. When cold, the pot is broken, and the lead
button is freed from slag, and squared up on the anvil.
It is then cupelled. Both the scorification and crucible
processes, therefore, are merely preparatory to cupellation
(see Chapter V.).

§ 2. A2Jpa7'atus Emjdoyed in the Crucible Process : —
(1) A balance with set of gramme weights (see § 2 of the
preceding Chapter) ; also a couple of special weights : one
of 29.17 grammes, and the other of 32G7 grammes.*
The balance should be capable of carrying 100 grammes.

* These represent, respectively, the sliort or American ton and the long or
British ton, the former consisting of 29166G66, and the latter of 32666666,
Troy ounces. When, tlierefore, an amount of ore equal to 29 17 is taken for
assay, each milligramme of gold or silver obtained on the cu]n,'l corresponds to
an oz. Troy per ton of 2000 lbs. (avoirdupois) of ore. And, in like manner, when
32 67 grammes of ore are taken for assay, a milligramme of the cujiel-metal
equals an oz. Troy per ton of 2240 lbs. (See Tables IV. and V., Chapter Vll.)

2>^ FURNACE ASSAYS.

If turninij with a milligramme when loaded with the above
weight, it will ho sufHciently delicate for criicil)lo and hco-
rification weighings, but a projx'r assay-balance indicating
tlie tenth of a niilligranime is necessary for the estimation
of th(; final cuiK'llation-products (see Chapter VI). {'2) A
porcelain capsule (and tare) to hold the assay-matter whilst
being weighed. ('>]) A co[)per scoop with flat floor and
raised edge, provided with a short wooden handle. This
S(irvcs for mixing the assay-matter with lithai'ge and
llux, and [)Ouring it into the crucible. It may be about
'^ inches long and 4 inches wide at the upper end, taper-
ing to about H- inch at the point. (-I-) A light steel
spatula with wooden handle, for mixing the assay matters
in the copper scoop. (5) A melting or fusion furnace.
The portable furnaces of sheet-iron thickly lined with
lire-clay, made by Luhme, of Berlin, answer perfectly;
or, in place of these, the fire-clay, iron-bound, melting
furnaces of the Battersea Company may be used. As
regards size, those with a diameter of 8 or 9 inches and a
depth of about dh inches will be found most convenient.
The domed top with its short chimney is removable.
When this is taken off in order to remove the pots, after
the fusion of the assay, it must be phiced on a brick
floor or on the broad sandbath which accompanies the
jjuhme furnaces. The method of fixing the crucibles and
igniting the furnace is described in § 6 of this Chapter.
I The pro})er fuel is good charcoal in pieces of about two

inches square ; but a few larger pieces to put over the
pots should also be at hand. (6) A supply of fire-clay

{

CnUCIBLE PROCESS. APPARATUS.

•

crucibles or " pots." Those of the B.attersca Works can^
not bo surpassed. The rouuvl pattern, 4 indies high,
.'i inches diameter at top, and 1| inch at bottom, is most
suitable. A good stock of this size should be provided,
as each assay (if made, as it should be, in duplicate)
entails the sacrifice of two crucibles. It is also desirable
to have at hand a few pots of larger and some of smaller
size, but very large and very small crucibles are com-
paratively useless. (7) A few crucible sui)ports. These
are small circular blocks of fire-clay, 2 inches in diameter
and 1 -1 inch high. In their absence, a squared piece of
of fire-clay brick, or a stout scorifier (reversed), may be
used. If the crucibles are placed directly on the furnace
bars, they are liable to adhere to these ; and the heat is
greater an inch or two above the grate than immediately
upon it. (8) A pair of crucible tongs, scissor-shaped,
about two feet long with the ends of the blades fiattened
inside and bent slightly downwards. A pair of elastic
tongs for feeding the furnace with charcoal (see Chapter
IV., § 2 [7]) are also necessary. (9) An iron pan,
such as a small cast-iron frying-pan, to hold under the
hot crucible when this is removed from the furnace, as
described in § 6 of this Chapter. (10) A small supply
of fire-clay roasting-dishes, about three inches in diameter.
These, of course, require a muffle-furnace, but they are
used only in special cases (see § 5). The flat-based dishes
are more conveniently handled than those of watch-glass
form, but the latter are more durable. Tlio inside is
nibbed or smeared with chalk, red ochre, oi- plumbago,

30 FURNACE ASSAYS.

before use. (II) A piece of stout iron wire ten or twelve
inches loii«^ (slig'itly flattened at one extremity, and
inserted at the otiiei- into a wooden handle) to serve as a
stirrer during the roasting process. (12) An anvil, on a
solid block of wood, and .a good hammer of about a pound
in weight at the heail, with one end square and the other
chisel-shaped. Thtise are described in Chapter IV.,
§2 (10). They are used for breaking the crucible and
extracting and sqiiaring up the workable lead-button, as
as described in § 5 of the present Chapter.

§ 3. Reagents : — In the examination of rock-matters
for gold and silver by crucible assay, but few reagents are
required. These com[)rise, essentially: (1) Litharge;
(2) Fluxing materials ; (3) Covering materials.

(1) X{</iar^e .•— This is the red or yellow lead oxide,
Pb O. During the fusion of the assay-matters it becomes
reduced to metallic lead, and in this state absorbs the
easily reducible metals, and more especially the un-
oxidizable gold and silver, if any be present in the ore.
These are afterwards separated from the reduced lead by
cupcDation, as described in Chapter 5. Fresh supplies
of litharge should always be assayed by reduction and
cupellation before use, as ordinary samples frequently
contain a small amount of silver. When a laboratory
sample is thus found to contain silver, the same amount
(say, 25 grammes or other definite quantity) must always
be weighed out for assays, and the known amount of
silver, of course, deducted from the assay results,

CRUCIBLE REAGENTS.

ays
of

(2) Fluxing Materials : — These consist essentially of a
mixture of carbonate of soda and calcined borax, to which
may be added a small amount of sugar or other car-
bonaceous s^ibstanco to promote the reduction of the
litharge. Where the gangue or rock-matter is essentially
siliceous or " acid," the flux may consist chiefly of carb.
soda, but a certain amount of borax should .always be
added to take up iron oxides, &c., and to assist the
fusion. With strongly " basic " gangues, on the other
hand, as where the rock-matter consists of calc spar or
heavy spar, or when ferruginous matter is present, the
amount of borax may equal or exceed that of the soda.
A useful flux, employed largely by the writer during the
last ten or twelve years, and which has been found both
in his own practice and in that of others to yield good
results in all general cases, has the composition given
below :

CHAPMAN'S CRUCIBLE FLUX.

3 lbs. carb. soda.

2 lbs. dried borax.

J lb. cream of tartar.

2 oz. white sugar.
The reagents in these proportions must be intimately inter-
mixed. The flux is conveniently kept in a large wide-mouthed
jar with covered top, and a porcelain scoop for its removal should
be kept in the same receptacle. The above quantities will dress
from 18 to 20 crucibles, when about 25 grammes of ore are taken
for assay.

(3) Covering Materials: — When the crushed ore,
litharge and flux are mixed together and poured into the

' \

; I

32 FURNACE ASSAYS.

crucible it is advisable to place an additional spoonful of
flux over the mixture, and to cover this with a layer of
common salt, previously ignited to prevent decrepitation.
The salt, in fusinuf, forms a very liquid cover, and thus
prevents any reduced globules of lead from adhering to
the upper |)art of the crucible. (See § 5.)

§ 4. lioastimj: — It has been already stated that in the
case of strongly pyritous or arsenical samples the crushed
assay-matter must bo roasted in order to drive oflf
sulpliur, tkc, before it is subjected to fusion with litharge.
The lead-button would otherwise be liable to break on
the anvil, and would not cupel properly. As a rule, how-
ever, a substance that requires roasting may bo assayed
by scoritication, a workable lead-button being then ob-
tained by one operation, as described in Chapter III.

When it becomes necessary to resort to roasting, the
operation is performed as follows: The quantity of
crushed and sieved ore required for assay (see § 5) is
weighed out and spread over the bottom of a roasting-
dish, previously smeared with red ochre, chalk, or
plumbago, to prevent adhesion. The dish is then placed
in a moderately hot muffle (see Chapter III.), and its
contents are carefullv stirred from time to time : the dish
being drawn when thoroughly ignited to the front of the
muffle, or even on to the ledge before the muffle-opening,
so as as to keep it exposed to a full supply of air. Fusion
must be carefully prevented by constant stirring. If this
be neglected, or if the dish be left too long in the hot

CRUCIBLE IMIOCK:;!.

S.*^

its
dish

the
ling,
ision

this

hot

part of the muflle, tlie surface of the ore may easily cake,
and in that case a complete roasting l)Ccomes impossible.
The opL'ration is thus somewhat tedious, especially in the
case of arsenical compounds ; but too much care cannot
be bestowed upon it, as if it be incompletely performed,
a brittle lead-button, which cannot be properly cupelled,
is almost certain to result in the subsequent fusion with
litharge. When the roasting is completed, the ore no
longer scintillates when put back into the hot j)art of the
muffle, and it ceases on continued stirring to give ofl
fumes or perceptible odour. When cold, it })rGsents an
earthy aspect, and has usually a dull red or rusty black
colour. It is then ready to be transferred to the mixing-
scoop and crucible, as desciibed in the next section.

§ 5. Weighing and Drest^ing Siunpleafor crucible assay :~^
The amount of test-matter taken for crucible assay may
vary from about 20 to 50 grammes, but a weigiit of 25
grammes is about the most convenient amount for ready
handling. Table 2 in Chapter VJ I. shews the value in
Troy ounces, &c,, (per ton of 2,000 lbs. and 2,240 lbs.,
respectively), corresponding to each milligramme and
tenth of a milligramme obtained after cupellation from a
weitrht of this amount. But when the returns are re-
quired to correspond to only one of these tons, a weight
of 29.17 grammes may be taken to represent the smaller
or American ton, and a weight of 32 -07 grammes to
represent the British ton. Each milligramme of gold or
silver, as obtained by cupellation, will then equal a Troy

FURNACE ASSAYS,

ounce. See Tables 4 and 5, Chapter VIT. ; also footnote
on page 27, above.

The weighed ore (assuming that it does not require
roasting, § 4) is transferred from the weighing capsule to
the copper mixing-scoop, and a weighed or measured
amount of litharge (equal to or sonujwhat exceeding the
weight of test-matter) is placed upon or beside it, together
with three or four large spoonfuls of flux (§ 3, above),
and the whole is carefully mixed by a steel spatula. The
amount of flux need not be weighed out, but as much
should be taken as the crucible can conveniently accom-
modate — a clear space of half-an-inch in depth being left
for the salt cover, and another space of about the same
depth between this and the top of the crucible. If the
crucible be filled to the top, loss will be occasioned by its
contents boiling over. The best plan is to mix the ore
and litharge with about three or four times their volume
of fliux in the scoo}), to pour this into the crucible, and
then to stir in more flux if there be room for it. An
additional layer of flux should be added to the to}) of the
mixture, and a layer of salt is finally spread to the depth
of about half-an-inch over all — care being taken, as ex-
plained above, to leave a clear space between this and the
rim of the crucible. A couple of pots should be dressed
and filled in this manner and the assay thus made in
duplicate, so that one result may serve as a check on the
accuracy of the other.

In the examination of galena for silver by crucible
assay (when the small amount of silver renders a scorifi-

CRUCIBLE PROCESS.

cation assay unsatisfactory), the ore (25 or r)0 grammes)
may be mixed with about 3 times its woiglit of the abovcs
flux, and 5 grammes of saltpetre ; and two or tlireo large
iron-nails may be placed upright in the mixture, the
whole being covered with a layer of salt. All the silver
will go into the lead button, but there will be a consider-
able loss of lead. This, however, is no disadvantage, as
tliere is thereby less to cupel.

§ 6. Furnace Manipulation : — The dressed crucibles,
being ready for the furnace, the operator puts on his
thick furnace-gloves, and seeing that the spaces between
the bars of the grate are free from slag or cinder, he
places a couple of crucible supports (see §2 [7] of this.
Chapter) upon the grate, tills in loosely the space around
these with small blocks of charcoal, and sets each crucible
firmly on its support. More charcoal is then carefully
added, until the pots are entirely covered. The dome of
the furnace is then put on, and three or four pieces of in-
candescent charcoal (previously ignited in another furnace,
or in an ordinary stove or fire-place) are dropi)ed through
the door at the tojj, and the air- way is opened below. In,
about ten minutes or a quarter of an hour the whole
body of the charcoal will be in ignition, and flame will:
appear at the top of the short chimney. A fresh supply
of charcoal must then be added through the door in the
dome, and the supply must be kept up, by droj)i)ing in
five or six additional pieces every eight or ten minutes,
for about fifty minutes or an hour after the first appear-
4

1 1

oQ FURNACE ASSAYS*

ance of flame at the top of the furnace-chimney. The
furnace is then allowed to burn down, and the dome is
removed, by its side handles, and set on a large Luhme
sandbath or on the brick floor. When the crucibles
thus become sufiiciently exposed, the operator grasps
them, one at a time, on tho outside, a little below the
top, by a pair of large scissor-tongs (§ 2 [8]) held in his
right hand, whilst he holds with his left hand a flat iron
vessel of any kind (such as a cast-iron frving-j^an) under
the lifted crucible. Tho crucibles are thus safely removed
to a brick placed in tho lal)oratory sink, or are carefully
set on the brick floor. In })utting them down, thoy nuiy
be tapped gently two or three times, but must not be
roughly shaken, as in the latter case some of the reduced
lead might spurt up among the slag and remain there.
It sometimes happens that the support adlieres to the
bottom of the crucible and is lifted with it ; but that is
of no consequence. A slight tap of the hammer when
the crucible has cooled, easily separates the two. Until
the crucible be set down it must be kept in the grasp of
the tongs, although sup[)orted at the same time by tho
pan held beneath it ; but tho latter is only intended to
guard against the risk of accident.

§ 7. Manipulation of the Crucible Button : — When
sufficiently cool to handle, which will not be until the
lapse of twenty minutes or half-an-hour, the crucible is
laid on its side on the anvil, and is broken by a series of
blows given with the sharp end of the hammer. If the

"^^^^^^■^'^•^^'^"

t^UPELLATION.

operation be skilfully performed, the pot separates into
halves longitudinally, and the button of workable lead
becomes exposed. The slag above the latter should be
perfectly free from small globules of metal. The broad
or square end of the hammer is then used to break up
the bottom of the crucible and liberate the button. This,
which should be soft and malleable, is hammered free
from slag, and squared up on the anvil. It is then ready
for cupellation.

CHAPTER V.

Cupellation.
[Object and General Nature of the Process. Cupelling Apparatus
and Materials. Details of Manipulation.
§ 1. Object and essential character of Cupellation : —
When metallic lead containing gold or silver is exposed
to a high temperature in a current of air, it becomes
oxidized ; and if the operation be performed on a porous
support which is not attacked by lead oxide, the latter
is gradually absorbed, carrying with it any copper or
other so-called base metal that may be present, and leav-
ing the unoxidizable gold and silver in the form of a
fused globule on the surface of the support. In assay
practice, the support is made of well burnt and finely
ground boneash, and is known as a cupel (see § 3). When
gold and silver are present together in the cupel-globule,
thus obtained, they are separated by dilute nitric acid
(Chapter VI.), the silver being readily dissolved by
that reagent, whilst the gold remains untouched. Cupel-

Fl/RNACE ASSAYS.

II ii

lation is thus resorted to in order to ascertain if these
metals (or either of them) be present in the compara-
tively large button of lead obtained in the scorification
or crucible process. As already explained (Chapters III.
and IV.) all the gold and silver present in the amount
of ore taken for assay will be contained in this button.
The lead separates the precious metal from the ore, and
cupellation separates it again from the lead.

§ 2. Cupelling Apparatus and Aj^pliances : — The fol-
lowing are necessary: (1) A cupelling furnace, with
a supply of fire-clay muffles. Where a furnace of this
kind is not built up permanently as a fixture in the
laboratory, its place is conveniently supplied l^y one of
the square fire-clay furnaces made by the Battersea
Company; or by a sheet-iron Luhme furnace, thickly
lined with fire-clay. These have been already described
in Chapter II., together with their accompanying muffles.
(See page 15.) They should stand, if possible, on a brick
or stone floor, and be raised sufficiently above the ground
to enable the operator to look into the muffle without
inconvenient stooping. They require no special flue ;
but they should be placed, nevertheless, under a large
hood communicating with a chimney, or should otherwise
stand in an open, well-ventilated part of the laboratory,
in order that the carbonic acid and other products of
combustion may by rapidly dissipated. (2) Cupel
moulds and supply of bone ash. These moulds are some-
times made in two pieces, entirely of brass or gun-metal —

CUPELLING APPARATUS.

consisting of a thick, slightly conical ring (the monld,
proper,) about an inch and-a-half or an inch and three-
quarters in diameter and an inch deep ; and a pestle or
stamper, three or four inches long, with its broad end
smoothly convex to form the concave surface of the
cupel. A flat rim surrounds this convex portion of the
stamper in order to j)revent the latter from being driven
too deeply into the mould. Another and more common
form of cupel-mould is in three pieces, made of hard steel.
These consist of the mould proper, a thick, slightly
conical ring (about 1 J or If inch deep, 1| inch inside
diameter at the top, and IJ inch diameter at bottom) ; a
flat disc of steel, { inch thick, forming a moveable bottom
to the mould ; and a pestle or stamper, consisting of a
steel head (with convex surface surrounded by a flat
border) screwed into a solid box-wood handle, five or six
inches long. The method of using these moulds, in the
formation of cupels, is described in detail under § 3,
below. Moulds which turn out cupels of about an inch,
or three-fourths of an inch deep, and an inch and a-half,
or inch and a-quarter in diameter, are the most con-
venient as regards size, but somewhat larger and some-
what smaller moulds should also be kept in a properly
appointed laboratory. The bone-ash ought to be quite
white, thoroughly well-burnt, and finely ground and
sifted. Purchased bone-ash should be tested by dilute
hydrochloric acid. If it effervesce strongly, it will con-
tain carbonic acid, and in that case it should be discarded
(or subjected to more prolonged ignition), as cupels made

FURNACE ASSAYS,

from impure bone-ash, of this kind, are very liable ta
become cracked or fissni-ed in the muffle. (3) A wooden
malleb to drive the pestle or stamper into the cupel-
mould. (4) A steel spatula, with wooden handle, for
mixing or kneading the moistened bone-ash, filling the
moulds, &c. (5) A lai*ge ix)rcelain-mortar, or earthen-
ware bowl or pan, to hold the bone-ash whilst being
moistened and prepared for the moulds, as described under
§ 3, below. (G) Cupel tongs of light sheet-iron or steely
about thi-ee feet in length, either curved or bowed at the
free end to fit the cupel, or slightly bent downward at
that extremity. The beginner should practice on empty
cupels with these tongs, as he is very liable to take hold
of the cupel too low, so as to cause it to tilt, or otherwise
to grasp it too high and with too strong a pressure, causing
it to break or crumble at the edges. (7) Furnace tongs
for feeding the furnace with charcoal. These, already
described in Chapter III., consist of a pair of short
spring-blades slightly enlarged and flattened at the free
ends. (8) A wash-bottle for conveniently moistening the
bone-ash in preparing it for the cupel-mould. (9) A
block of solid wood (or an anvil : see Chapter III.) for
the support of the cupel -mould whilst the pestle or
stamper is being struck by the mallet. (10) An old silk
handkerchief, or soft, clean rag, for wiping the mould and
stamper during and after use.

§ 3. Preparation of Cupels : — The assayer should
always prepare his own cupels. Those purchased, ready-

L*-iw-

PREPARATION O? CUPELS.

made, are frequently of doubtful quality, either from
being composed of impure bone-ash, or from being mixed
with mucilaginous matter in order to render them
sufficiently compact to boar packing and transportation.
Half-an-hour'a practice will enable anyone to make
them successfully. The bone-ash is placed in a largo
porcelain mortar or other convenient recei)taclo, and is
well sprinkled with water from an ordinary wash-bottle,
or simply by the hand, it is then thoroughly mixed and
kneaded by a light steel spatula, more water being added,
if necessary, to make the particles " bull " or just cohere
together. Very little water, however, must be used.
Beginners generally use too much, simple moistening
being all that is required. The proper amount is readily
learnt by practice. If the bone-ash be too wet, it slicks
to the mould and stamper, and the cupels are ill-formed
and otherwise unsatisfactory. "Failures" of this kind
should be returned to the porcelain mortar, and ground
up with some additional bone-ash. If, on the other hand,
the bone-ash be too dry, the cupels crumble or fall to
pieces when handled. Some assay ers damp their bone-
ash, roll it up into balls, and leave these for ten or twelve
hours, to dry partially, before being made into cupels.

The properly moistened bone-ash is taken up by the
spatula and inserted into the cupel-mould until the latter
is entirely filled. The mould is then placed upon the
laboratory anvil or other solid support, and the stamper
is set upon it, in as vertical a position as possibhi, au<l
struck smartly three or four times by the m diet. Tijo

42 FURNACE ASSAYS.

latter is then laid aside and the stamper is removed care-
fully in imparting to it a circular motion by a slight
turn of the wrist. This effected, a little bone-ash is
dusted ov^cr the work-table, and tlie mould is reversed
upon it. The pressure of the thumbs on the moveable
bottom of the mould (or where the mould is without this
extra piece, on the bottom of the cupel itself) is gener-
ally sufficient to effect the removal of the cupel ; but
sometimes a light tap or two with the wooden handle of
the spatula is necessary to loosen it. The mould is then
carefully raised, and tlie cupel is taken up lightly, turned
right-side upwards and set to dry on a porous brick.
The next day it may be placed to dry more thoroughly
on the top of a warm furnace, or on the platform around
the short chimney with which many cupelling furnaces
are furnished for that purpose, but quick drying is always
to be avoided. If a cupel be made and dried hastily so
as to be used on the same occasion, it is very liable to
crack or fall to pieces in the muffle. A batch of cupels
should therefore be made now and then, and be kept
for use, after drying, in one of the laboratory drawers or
cupboards reserved for that purpose. After each cupel
is made, the mould and stamper must be carefully wiped,
and they must always be cleaned from adhering particles
•of bone-ash before being put away ; otherwise they will
soon lose their polish and become unfit for use, as bone-
ash readily attracts moisture from the atmosphere. A
•cupel is assumed to absorb its own weight of lead, but it
is safer to allow a few grammes extra weight in favour

CUPELLATION t»ROCESS.

of the cupel. When the lead button is very largo and
there is danger of the cupel becoming saturated before
the close of the operation, another cupel, in reversed
position, may be placed under it.

§4. Details of the Cupellation Process: — The chief
points to be observed in cupellation are the following.
The cui)els must first be placed alone in the glowing
muffle to become thoroudilv ignited. If a lead button
be placed upon a cold or even moderately warm cupel, it
will rapidly become covered with a crust of infusible
oxide, and the operation will be spoilt. This, in tech-
nical language, is known as " freezing."

The cupels are placed, therefore, at first, alone in the
hot muffle, and the doors are closed for eight or ten
minutes. By that time the cupels will have become suffi-
ciently ignited for the reception of the scorification or
crucible buttons. These are seized singly in the assay
tongs (those with downward bent points answer best),
and the door being opened or removed, each button is
placed quickly but carefully in its cupel, a hot coal or
two is placed at the mouth of the muffle, and tlie door is
again closed. Where several cupels are under treatment
in the same muffle, they are set in two rows along (but
not quite touching) the sides ; and those near the front
of the muffle should have a hot coal laid against their
base throughout the operation. When only a couple of
cupels form the muffle charge, they should be set towards
the centre of the muffle or not too near the door.

4i FURNACE ASSAYS.

Aftor tlin liipHcj of "another interval of about ten
minutes, the inufllu door is again opened cautiously, and
if, as coinniouly Ijappens, the lead buttons are then in
full fusion, fcujuini,' a liquid *' bath," the door is left open
8o as to allow a (Mirrent of air to flow over the cui)ei3.
The cupellation goes kindly when a thin vapour rises in
delicate coils froui the oxidizing metal, and a ring of
yellow scales of litharge forms around the inner edge of
tlie cupel. If dark, thick fames are rapidly evolved, the
temjxn-ature will be too high ; and in that case the draft-
opening below the grate must be closed, and the upper
<loor in the dome of the furnace should be opened for a
few minutes. If, on the other hand, there is no per-
ceptible lowering of the molten bath, and scarcely any
fumes cnn be seen to arise from it, the temperature will
be too low, and there will be dan^jer of froezinjj. A
glowing coal must then be placed immediately against
the cupel, and the air-way beneath the grate must be
opened to its full extent, — care being taken at the same
time to see that the coal has not burnt down too low in
the furnace, so as to leave the top of the muffle exposed.
It may be advisable, also, to close or partly close the
muffle door for a moment ; or in extreme cases, to drop
from a ladle some fused lead on the cupel, and to close
the muffle entirely for a brief space of time. If the
furnace, how(3ver, is well supplied with fuel, and the
cupels arc fully ignited before the buttons are placed
upon them, there will be little risk of failure — provided
always that the amount of lead in the button is suffici-

CUrELLATION PROCESS.

n\t to eflfiict tlio ciipollation of any copper or nickel that
insiy bo present in it. These metals require about six-
te(M» tiine.s their weight of lead for proper cupeliation.
when they occur tlierefore in any form, either singly or
togethei*, in samples of ore, and insufficient lead has been
used in the scorification (Chapter III.), the fused bath
on the cupel is liable to become encrusted (especially
towards the end of the operation) with a semi-crystalline
coating of infusil)le oxides, and the process becomes
suddenly arrested. It may sometimes be started again
by pouring some hot lead into the cupel, or by putting a
}iot coal over it ; but this does not always prove success-
ful, 80 that, as a rule in cases of this kind, it is better to
remove the cupel, break it up carefully when sufficiently
cold to be handled, and i"e-scorify its contents with tho
addition of 40 or 50 grammes of granulated lead and a
little borax. '^

Assuming, however, the cupeliation to proceed kindly,
it is always advisable to let the operation go on by itself
— simply adding a little fuel from time to time through
the door in the furnace-dome, in order to keep the top of
the muffle well covered. Gradually, the fused lead in
the cupel will sink lower and lower, and finally pass out
of view. As a rule, with buttons of from 15 to 20
grammes weight, the lead will be absorbed or eliminated

• Tlie silver ore of tho 3 A Mine, Lake Superior, is associated in this manner
with a nickelferous mineral, by which its assay is rendered more or Jess diffi-
cult to beginners. Tlio effect of the nickel must be destroyed by a somewhat
prolonged scorification and the use of lead in excess. See Chapter III.

46 FURNACE ASSAYS.

in about 40 or 4') minutes after the opening of the
niuffle-dooi-.* Tlic niuffle is then again closed, and a
strong tire is got uj» for five or six minutes to caiise tlie
absorption of the last vestiges of lead. This effected, the
door is opened or removed, and the cupels are drawn
carefully to the mouth of the mullle, where they are left
to cool down slowly for a short time, in order to prevent
the cupel-button from "spitting." If, for instance, the
button or globule of gold or silver, which remains on the
cupel, be comparatively large, it is very apt to crack or
throw ofl' excrescences, or, in technical language, to
"spit" or "sprout," if rapidly cooled, and from tliis
cause too low a result might be obtained. In the assay
of bullion, ttc, this has to be carefully guarded against ;
but in the assay of ordinary ores and rock-matters the
globule is usually too minute to need any very rigorous
precautions of this kind. Commonly, as it cools, it emits
a sudden gleam or flash of light, caused, it is generally
thought, by the escape of oxygtin absorbed during fusion;
but as this gleam or " blick " is exhibited by gold as well
as by silver, it is probably due to an incipient crystalliza-
tion, or to a sudden change, on cooling, in the molecular
condition of the metal.

Finally, the cupels are removed from the furnace and
set to cool on a flat-brick or on some large scoritiers
arranged on a tray for their reception. In large assay-

* It is i)erliaps needle.ss to observe that a got)d clock slioukl always occupy
a prominent place in the assay-laboratory, together with ahlack board or sla'e
on which the operator ought to mark dowa the time at which the various
stages of his work commence.

CUPELLATION PROCESS.

offices, a cast-iron tray, with sunk and numbered com-
partments, is commonly used for this purpose. When
sufficiently cooled, the cupel-button (if there bo one as
the result of the assay) is easily detached by a pair of
light forceps or the point of a pen-knife. If free from
lead, it adheres very slightly to the surface of the cupel.
When thus detached, it is examined by a pocket-lens, *
and is cleaned, if necessary, by being rubbed in the palm
of the left hand by the moistened tip of one of the right
hand fingers. It is then ready to be weighed in the
assay-balance, and to be treated in other respects, as
directed in the ensuing Chapter.

In cupellation, silver always suffers a small amount of
loss, arising chiefly from absorption by the cupel, and
depending more especially, as regards the actual amount,
on the quantity of lead employed, the temperature of the
muffle, and the condition of the cupel. This has to be
tiken into consideration into the assay of bullion ; but in
ordinary mineral assays, in which the cupel-but ;;0n
commonly weighs a few milligrammes, and scarcely ever
reaches or exceeds 100 milligrammes in weight, the loss
is insufficient to render a correction necessary, and in
practice it is always neglected. Cupelled silver, in fact,
is never, in the strict sense of the term, absolutely pure,
and the minute amount of impurity present in it thus

• The little globule or button is taken up and held very conveniently, during
examination, by a short piece of tobacco-pipe with some soft wax at one
extremity. This is also a useful support for small crystals, &c., as it can be
turned round between the thumb and forefinger of the left hand, so as to
bring all parts of the object under view.

t I

FURNACE ASSAYS.

partly makes up for the cupel-loss. Any legitimate assay-
loss, moreover, is certain to be exceeded by the loss
which accrues from the metallurgical treatment of the ore
on the large scale, and the assay returns, if the cupel-
loss be netilected, are thus brouijht into nearer aijreeraent
with the fui-naco yield. In special cases, nevertheless, it
may happen that ricli silver ores, yielding 10 to 20 per
cent., or even a higher percentage, of metal, may come
under assay. In cases of this kind the same class of ore
(as the product of a particular mine or mining district)
will probably be constantly under examination, and the
assaycr must draw up for himself a table of corrections
based on actual experiment, i.e., by comparing his assay-
results with percentages obtained by careful liquid-
analysis. It is not possible to give a table of this kind
adapted to all cases, or indeed to tko work of any
individual assayer or assay-furnace.

CHAPTER VI.

Estimation of Gold and Silver in Cupel Buttons.

[Explanatory Remarhs. Apparatus. Weighing. Treatment
with Dilute A itric Acid. Quartation. Bloivpipe Treatment.]

§ 1. Separation of Gold and Silver. Explanatory Be-
marks : — The little button or globule, obtained on the
cupel, may consist of gold or silver, only, or of an alloy
of these metals. Silver frequently comes out alone, but
cupelled gold almost invariably contains a certain amount

CUPEL BUTTONS.

4r»

of silver. When the latter exceeds tho gold iu weight,
the cupel-button will he quite white or very light in
colour. Perfectly pure gold is known as 24 carat gold,
the })ure metal being alwayn assumed to consist of 24
equal juirts or carats. Britisli " standard gold " is of 22
carats : that is to say, every 24 parts contain 2 parts
of silver (or silver and copper combined). Twelve carat
gold, therefore, consists of half gold and half silver (or
silver-copper alloy). In the language of bullion assayera,
a gold which differs from " standard goKl " is so many
carats better or worse. Thus 23 carat gold is one carat
better; and jewellers' gold (the best, of 18 carats) is four
carats worse.

The cupel button on removal from the cupel is weighed
•in a delicate assay bahmce. It is then placed in a small
capsule or other convenient vessel (see § 2 below), and is
treated with nitric acid. By this treatment, in general
cases, the silver becomes rapidly dissolved, whilst the
gold separates in the form of a dark brown or black
powder. The latter is then carefully washed by decan-
tation, dried, and weiglied. Its weight deducted from
that of the cupel-button, gives, of course, the weight ot
the silver If, however, the silver bo not somevi^hat
largely in excess, the cupel-button becomes simply black-
ened in the acid, and very little silver is disolved. In
tliis case, the weighed button must be fused with a piece
of pure silver of about twice its weight, together with
some pure lead, and the resulting button subjected to
cupellation. All the silver becomes then readily taken

FURNACE ASSAYS.

out by nitric acid. The lead-fusion and subsequent cupel-
lation, when the globule (as so commonly happens) is of
minute size, are most rapidly performed by the blow-
pipe, as described under § 4 below. But where the gold
is suspected to be of high standard, a small piece of pure
silver, of known weight, may be added to the original
lead-button during cupellation, and its weight afterwards
deducted from that of the entire amount of silver, as
determined by the loss in nitric acid, or by precipita-
tion from the acid as silver chloride. Finally, the cor-
responding values per ton of the gold and silver, thu.s
found, are calculated by reference to the Tables given in
Chapter VII.

§2. Apparatus: — (I) Assay Balance. — ^The principal
piece of apparatus required by the assayer at this stage
of his work, is a delicate assay-balance. This need not
carry a greater weight than 2 or 3 grammes (if used
solely for weighing cupel-buttons and the separated gold),
but it must indicate readily the tenth of a milligramme.
The 10-gramme balances of Oertling, of London, or
Becker, of New York (costing about j£19 or $35), are
sensible to ^i^ of a milligramme when fully charged, and
are especially to be recommended ; but very serviceable
balances may be obtained at about half this cost. The
assay-balance should, of course, be provided with a glass
house, and its beam should be divided for the determina-
tion of the lesser weights by means of a 1 -milligramme
rider, made of finely-drawn aluminium wire. It should

ASSAY BALANCE, ETC.

51/

also be provided with a pair of light weighing-capsules-
of thin, gold-plated brass or of horn, a pair of ivory -tipped
forceps, and a small camel's-hair brush. The weights
should range from a gramme, or two grammes, down-
wards, and should be accompanied by two or three 10-
milligramrne and 1 -milligramme riders : all, of course,
accurately tested. (2) Two or three small capsules of
j)orcelain (an inch and a half to two inches in diameter)
with attached handle. These little capsules are especially
useful as receptacles for the cupel-buttons when removed
from the cupels and taken to the balance-room ; and
they serve also for the treatment of the button with
nitric acid. They can be covered with a watch-glass
during the solution of the silver, in order to prevent the
escape of nitrous fumes ; and they are held very con-
veniently over the flame of a small Bunsen-burner or
spirit-lamp by their short handle. In regular assay
offices were bullion is treated, conical beaker glasses,
known as " parting flasks," are the orthodox vessels for
this operation. The beakers narrow upwards and have
a thick glass band a little below their neck, by whichi
they are taken up by a pair of suitable tongs, when,
heated. In operating on very small buttons, however,
the porcelain capsule is a far more convenient vessel, es-
pecially as regards the drying and removal of the washed
gold. (3) A larger capsule or two, to hold the liquid
poured from the smaller capsule during the washing of
the separated gold by decantation. (4) A. common)
spirit-lamp or small Bunsen-burner. (t5) A blowpipe
6

! I

52 FURNACte ASSAYS.

and set of blowpipe cupel-moulds, or, in place of the
latter, a cylinder of baked clay or pumice (about three
inches long and three-fourths of an inch in diameter),
with a slight concavity at each extremity for the recep-
tion of the boneash forming the cupel.

§ 3. Reagents : — ^The following, at this final stage of
the work, are all that are necessary: -(1) Nitric acid,
perfectly free from hydrochloric acid. It should be
diluted slightly and tested with nitrate of silver before
being used. A cloudiness or milky precii:>itate will be
produced if hydrochloric acid be present. (2) A solution
of common salt (NaCl), or some hydrochloric acid, for
re-obtaining the silver of the cupel-button (if this be
desired) from the nitric acid solution. (3) A piece or
two of pure lead foil, and some finely-sifted boneash, for
re-cupelling the gold buttons when necessary, (4) A
small strip of pure silver. This may be obtained from
an ordinary silver-coin by separating the copper alloy !

either by fusion with lead and subsequent cupellation,
or by solution of the coin in nitric acid and precipitation
of the silver as chloride, the latter, after thorough wash-
ing, being fused with some reducing flux in a porcelain
crucible, and the reduced silver hammered out for use.

§ 4. Detailed Treatment of the Cupel-button : — The
small button or globule, after being carefully separated
from the cupel, and cleaned from adhering matter, as
explained at the close of Chapter V., is taken in a little
porcelain capsule to tlie balance room, and its weight ia

TREATMENT OF CUPEL BUTTON.

very accurately ascertained. The button is then replaced
in the capsule, and some pure nitric acid diluted with
about an equal bulk ot* water is dropped upon it, and the
capsule is held for a few minutes, or until the acid begins
to boil, over the flame of a spirit-lamp or Bunsen-burner.
One of three results will then ensue : (i) the globule
will dissolve wholly ; or (u) it will dissolve in part only,
the gold separating as a dark-brown or black powder ;
or (Hi) it will merely become black on* the surface, and
in this latter case scarcely any orange-brown fumes will
be evolved from the acid, whilst copious fumes of this
kind will be given off if the button be dissolved in part
or wholly.

If the solution be complete, so that nothing remain
undissolved, the button will have consisted entirely of
silver. Its corresponding value per ton of ore may
therefore at once be calculated or otherwise determined
by reference to the proper table in Chapter VII.

If the button be in part dissolved, with separation of
brown flakes or powder, the liquid must be carefully
decanted from the capsule, and the operation repeated
with undiluted acid. The dark powder is then washed
two or three times with distilled water, this being
decanted cautiously after each washing. As the powder
is very heavy, the washing is easily efiected without risk
of loss. The last remains of the water are drawn off" by
«, fold of filtering or blotting paper, or are expelled by
•cautiously warming the capsule. The dry powder is
then shaken or swept by a camers-hair pencil into one of

54 FURNACE ASSAY'S.

the little weighing capsules of the assay-balance, and its
weight, to the tenth of a milligramme, is carefully
ascertained. If desired, it can be folded afterwards in a
piece of lead foil, and melted and cupelled in one opera-
tion by the blow-pipe, and the resulting gold globule can
be preserved in a short piece of glass tube closed at each
end by a piece of cork. Or, to show its true nature, the
dark powder may be compressed strongly by a glass
stirring-rod, or rubbed in an agate mortar, when it will
quickly assume the yellow colour and metallic lustre of
ordinary gold. The weight of the silver is, of course,
obtained "by difference," i.e., by deducting the weight of
the gold from that of the cupel-button.

When, on the other hand, the cupel-button merely
becomes darkened on the surface by treatment with
nitric acid (as in all buttons which show a rich gold
colour) the process known as "quartation" must be
resorted to for the purpose of extracting the silver, so as
to obtain the true weight of the gold in the button. It
is commonly assumed that unles the silver be to the gold
in the proportion of 3 to 1, the gold prevents the acid
from thoroughly dissolving it. Complete solution of the
silver is effected, however, when the proportions are as 2
(or even 1|) to 1. In the case of very rich buttons,
therefore, a small cutting of silver three or four times
at least, the size of the button, must be placed with the
latter, in contact with a piece of lead foil, on a blowpipe
Cupel, and the whole fused together and then subjected
to cupellation on the same support. The weight of the

ASSAY TABLES.

added silver need not, of course, be taken. The resulting
silver-gold globule will be quite white, and all the silver
will be readily extracted from it by treatment with
nitric acid, as directed above. The weight of the gold
deducted from that of the original cupel-button gives, of
course, the weight of the silver present in the assay-
matter.

In some exceptional cases the auriferous button left on
the cupel may be too large to be subjected to blowpipe
treatment. A button of this kind must be wrapped with
a cutting of silver in a })iece of lead foil, and cupelled in
the muflfle.

Finally, the amount of gold and silver in the assay-
matter being thus obtained, the corresponding amount
in the ton of ore must be determined — the portion of ore
taken for assay being assumed to represent the ore gener-
ally. The determination is, of course, very simple. If
X grammes (the assay amount) represent the ton of
2000 lbs. or 2240 lbs. of ore — how many ounces, penny-
weights, and grains, Troy, will x milligrammes (the
amount of gold or silver obtained in the assay) represent 1
The Tables given in the ensuing Chapter will show the
required result, in ordinary cases, without calculation.

CHAPTER VII.

Assay Tables.
Table I., of the following series, will be found useful
in calculating the ton values of returns obtained from

SfS FURNACE ASSAYS.

Scorification Assays. Tables II. to V., inclusive, apply
to Crucible Assays. Table VI., which also applies to
Crucible Assays, is calculated for grain weights. Table
VII. shows the ton values corresponding to percentages
from 1 to 0-0001. These Tables have been drawn up
expressly for the present work. Table IX. does not per-
haps belong properly to the series, but may be found
useful in certain cases. It is the result of repeated
determinations in the writer's laboratory.

The following example will serve to explain the Tables
generally : — Five grammes of a given ore are scorified
with the proper quantity of lead, &c. (see Chapter III.),
and the lead-button, thus obtained, yields a cupel-button
which weighs 8 milligrammes. This leaves 2 3 milli-
grammes of gold after treatment with nitric acid (see
Chapter VI. ). The amount of silver in the button was
consequently equal to 5-7 milligrammes. Hence (see
Table I.) the gold is equivalent to 13oz. 8dwts. 8gr.
(= lloz. ]3dwts, Bgrs. + loz. ISdwts. Ogrs.) per ton of
2000 lbs. of ore ; and to 15oz. Odwts. ISgrs. ( = 13oz.
Idwt. 8grs. + loz. 19dwts. 5grs.) per ton of 2240 lbs.
The silver, in like manner, is shown by the Table to
correspond to 33oz. 4dwts. 14grs., and to 37oz. 4dwts.
20grs., per short and long ton, respectively. As already
stated, gold and silver ounces are invariably understood
to be Troy ounces.

ASSAY TABLES.

TABLE I.

5 Grammes taken for Assay.

Milligrammes of

TON

of 2000 Lbs.

Ton

or 2240 Lbs.

Gold or Silver
Obtained.

Oz.

Dwts.

Grs.

Oz.

Dwts. Grs.

i 8

' 8

! 16

(»

! 1

0.9

0.8

0.7

' 0.6

0.6

0.4

0.3

0.2

0.1

•58

FURNACE ASSAYS.

TABLE II.

25 Grammes taken for Assay.

MlIXiailAMMEa OF

Ton

OF 2000 Lbs.

Ton

OF 2240 Lbs.

Gold or Silver
Obtained.

Oz.

Dwts.

Grs.

Oz.

Dwt8.

Grs.

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

14|

ASSAY TABLES.

TABLE III.

50 Grammes taken for Assay.

MlLLIORAMMKS OF

Ton

OF 2000

Lbs.

Ton

OF 2240 Lbs.

Gold or Silver
Obtained.

Oz.

Dwts.

Grs.

Oz.

Dwts.

Gra.

, 1

16 !!

14 !

' 8

13 '

12 j

16 !

•

5 1

3 i

0.9

0.8

0.7

0.6

0.5

13 i

0.3

0.2

141

0.1

FURNACE ASSAYS.

TABLE IV.

29.17 Grammes taken for Assay.

Assay-Result

Gold or Silver.

1 milligramme.

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.05

Tom of 2000 Lbs.

Oz.

Dwts.

TABLE V.

32.67 Grammes taken for Assay.

Assay-Result

Gold or Silver.

1 milligramme.

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.05

Ton of 2240 Lbs.

Oz.

Dwts.

Grs.

A-SSAY TABLES.

TABLE VI.

1 Oz. Avoirdupois taken for Assay.

Assay-Rksult

Ton

OF 2000

Lbs.

Ton

OF 2240

Lbs.

Gold on Silver.

02.

Dwts.

Grs.

Oz.

Dwts.

Org.

1 grain.

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.09

0.08

0.07

0.06

0.04

0.03

0.02

0.01

22i

FURNACE ASSAYS.

TABLE

VII.

A Table of Percentages and

Corresponding

values per Ton.

Percentage.

Ton of 2000 Lbs.

Ton

OF 2240 Lbs.

Oz.

Dwts.

Grs.

Oz.

Dwts.

Grs.

291

326

0.9

262

294

0.8

233

261

0.7

204

228

0.6

175

196

0.5

145

163

0.4

116

130

0.3

0.2

0.1

0.09

0.08

0.07

0.06

0.05

0.04

0.03

0.02

0.0)

0.009

0.008

0.007

0.006

5 '

0.005

15 i

0.004

3 !

0.003

0.002

O.OOl

O.O0O9

0.0008

0.0007

0.0006

0.0005

0.0004

0.0003

0.0002

0.0001

twrr^Bwr^^i'^^w^^Ffw

ASSAY TABLES.

TABLE VIII.

Average Value of Gold per oz., Troy.

Fineness in

•

Carats.

£ .s.

20. G5

4 5

18.93

3 17

17.21

3 10

15 49

3 3

13.77

2 10

12.05

2 9

10.32

2 2

Note —The value of silver is subject at present to constant fluctuation. The
average Bar or Standard Silver wi)l jtiobably oscillate for some time at a few
cents over $1 per oz. Troy. Standard Silver consists of 92 5 % pure silver,
and 7"6 % copper alloy. Cupelled or Cake Silver will average about a twelfth
more in value.

TABLE IX.

Approximate Sp. Gr. of Gold Alloys.

1 Fineness in

Alloy

1 Carats.

Sp. Qr.

Gold, %.

((JU-AG) %.

18-56

1)5-83

417

17-74

91 07

8-33

17-22

87-50

12-50

16-00

83 34

10 00

16-00

79-17

20-83 !

15-42

75-00

25-00

14-92

70-83

29-17

14-48

06 07

33-33

14 00

02-50

37-50

13 05

' 58-33

4167

13 28

5417

45 83

12-91

50 00

50 '00

INDEX.

•■

Acid gangues, 31.
Antimoniiil ores, 9, 22.
Anvil, 18.
Apparatus, 11, 14, 18, 27-30,

38-40, 50-52.
Argentiferous galena, 10, 23, 34.
Arsenical pyrites, 9, 22.
Assays in general, 7-8.
Assay Balance, 50.
Assay Matters, Preparation

of, 11.
Assay Mixtures, 20-23.
Assay Moulds, 17.
Assay Samples, 10.
Assay Tables, 55-G3.
Assay Tongs, 17, 29, 40.
"Astonishing." how effected, 12.
Auriferous pyrites, 9, 21.

Balances, 14, 15, 27, 50.
Basic gangues, 20, 31.
Blendiferous ores, 22.
Blowpipe Cupellation, 50, 54.
Boneash, 39.
Borax, 18, 20, 31.

Capsules, porcelain, 51.

Carat values, 49, 63.

Chalk, 17.

Chapman's crucible flux, 31.

Charcoal, 16.

Charcoal tongs, 17, 29.

Coup de grace stage in scori-

fication, 25.
Cover (salt), 31-32.
Crucibles, 29.
Crucible buttons, 36.
Crucible process, 26-37.

Crucible supports, 29.
Crucible tongs, 29.
Cupellation, 37-48.
Cupellation loss, 47.
Cupels, preparation of, 40.
Cupel buttons, 46, 47, 49, 52.
Cupel moulds, 39.
Cujjel tongs, 40.
Cupreous ores, 21, 23.

Dressing Samples :

For crucible fusion, 33.
For scorification, 18.

Fluxes, 31.

Freezing, 43.

Furnace (melting), 28.

Furnace (muffle), 15, 38.

Furnace tongs, 17, 29, 40.

Galena, 10, 23, 34.
Gangues, acid, 31.
(iangues, basic, 20, 31.
Gangues, silicious, 31.
Gold, Separation of, from

silver, 49, 53-55.
Gold alloys, 63.
Gold ores, 9.
Gold, powder, 53.
Gold values, 63.
Gramme weights, 14, 27, 61.

Hammer, 12, 18, 30.
Hydrochloric acid, 52.

Iron mortars, 13.
Jewellers' gold, 49.

€6

INDEX.

L-ead buttons, 25-20, 37, 43.

Lead foil, 52.

Load, granulated, 18.

Lead, test, 18.

Lead, workable, 25, 37.

Litharge, 30.

Luhme's furnaces, 15, 28.

Mallet, 40.
Melting furnace, 28.
Mortars, iron, 13.
Mortars, porcelain, 40.
Muffles, 10, 38.
Muffle furnace, 15, 38.

Native gold, 9, 23.
Native silver, 9, 23.
Nickeliferous ores, 20, 22, 45
Nitre, 35.
Nitric acid, 52.

Parting flasks, 51.
Percentages, Table of, 62.
Porcelain capsules, 51.
Porcelain mortar, 40.
Potash, nitiate, 35.
Potash, tartrate, 31.
Pyrites, 9, 21.
Pyritous galena, 23.
Pyritous ores, 21, 22.

Quartatior, 54.

Quartz, 9.

Quartzose gangues, 20, 21.

Red ochre, 32.
Riders, 50, 5i.
Roasting dishes, 29.
Roasting process, 32.

Salt, for coveis, 31, 32.
Salt solution, 52.
Sampling (»res, 10, 11.
Scoops, copper, 28.
Scoops, i)orcelain, 31.
Scorilication process, 14-26.
Scoritiers, 16.
Scoriiicr mould, 17.
Scorilier tongs, 17.
Sieves, 13.

Siliceous gangues, 31.
Silver, native, 9, 23.
Silver ores, 9.
Silver, Separation of, from

gold, 48, 53-55.
Special weights, 27.
Specific gravity of gold alloys,

03.
Stirrer, 30.
Sugar, 31.
Supports, crucible, 29.

Tartrate of potash, 31.
Test-lead, 18.
Tongs :

assay, 17.

charcoal, 17.

crucible, 29.

cupel, 40.

furnace, 17.

scissor, 29.

scorifier, 17.

Weights :
for crucible assays, 27, 33.
for scorification assays, 18.
19, 21-23.

Zinc-holding ores, 22.

COPP, CLAKK & CO , PRINTERS, COLBORNE STREET, TORONTO.

32.
1.

14-26.

f, from
Id alloys.

27, 33.

lays, 18,

_Sl.

""-— '•'■^■'' '"