A Textbook of Assaying | Page 2

Tinto Copper Company, and has been in use for many years
with success. This modification is now employed in copper-works in
Spain, Germany, and England, and is used in place of the dry assay for
the commercial valuation of copper ores.
We have adhered to the gram and the "c.c." as the units of weight and
volume. Those who prefer working with grains and grain-measures can
use the figures given, multiplied by ten. For example:--When 1 gram is
mentioned, 10 grains should be used, and 10 grain-measures take the
place of 1 "c.c." It is not advisable to mix the two systems, as by using
gram weights and grain-measures.
We have intentionally to a large extent omitted to mention the names of
those who have originated or modified the various processes. The
practice of naming a process after its discoverer has developed of late
years, and is becoming objectionable. It is a graceful thing to name a
gas-burner after Bunsen, or a condenser after Liebig; but when the
practice has developed so far that one is directed to "Finkenerise" a
residue, or to use the "Reichert-Meissl-Wollny" process, it is time to
stop.
We are indebted to the standard works of Allen, Crookes, Fresenius,
Lunge, Michell, Percy, and Sutton, and wish to express our sense of
special indebtedness to Mr. Richard Smith, of the Royal School of
Mines. One or two of the illustrations are taken from Mr. Sexton's
excellent little book on Qualitative Analysis. Our obligation to some

others is mentioned in the text.
Finally, we have to thank for assistance in the experimental work
Messrs. Bailey, Beswick, Clarke, Grant, Higgins, and Smith.
THE AUTHORS.
CAMBORNE, Nov. 1889.

CONTENTS.

PART I.

CHAPTER I.
INTRODUCTORY. Page Object of assaying 1 Sampling 1 Drying:
determination of moisture 5 Calculation and statement of results 7
Laboratory books and report forms 9 Quantity to be taken for an assay
11 Exercises 14
CHAPTER II.
METHODS OF ASSAYING.--DRY GRAVIMETRIC METHODS.
Methods of assaying 15 Gravimetric methods 15 Mechanical
separations 16 Dry assays 16 (a) Fluxes 16 (b) Reducing agents 21 (c)
Oxidising agents 22 (c) Apparatus 24
CHAPTER III.
WET GRAVIMETRIC METHODS.

Wet gravimetric methods 27 (a) Solution 29 (b) Precipitation 30 (c)
Filtration 31 (c) Drying and igniting 32
CHAPTER IV.
VOLUMETRIC ASSAYS.
Titrometric assays 35 (a) Standard solutions 36 (b) Standardising 37 (c)
Methods of working 42 (c) Indirect titration 43 Colorimetric assays 44
Gasometric assays 44
CHAPTER V.
WEIGHING AND MEASURING.
Weighing 47 Measuring liquids 49 (a) Graduated flasks 49 (b) Pipettes
50 (c) Burettes 51 Measuring gases 52
CHAPTER VI.
REAGENTS.
Acids, &c. 54 Bases, salts, &c. 59
CHAPTER VII.
Formulæ, equations, &c. 68
CHAPTER VIII.
SPECIFIC GRAVITY.
Introductory 75
Determination of specific gravity-- (a) Hydrometers 76 (b) Specific
gravity bottles 78 Calculations depending on specific gravity 84

PART II.

CHAPTER IX.
SILVER, GOLD, PLATINUM, CYANIDES, MERCURY.
SILVER--Detection 87 Dry assay 87 (1) Scorification 88 (2) Pot assays,
average ores 90 " ores with metallic oxides 91 " ores with metallic
sulphides 91 Explanatory notes on the fusion 93 The effect of charcoal,
flour, &c. 94 The effect of nitre 95 The effect of mineral sulphides 95
(3) Cupellation 98 The loss of silver 101 Condition affecting the loss
102 Methods of correction 103 Lead required for cupellation 105 (4)
Calculation of the results in ounces to the ton of 2240 lbs. Table 107
Ores with metallic particles 108 (5) Explanatory notes 110 (6)
Examples of dry silver assays 113 Wet assays 116 Gravimetric method
117 Gay-Lussac's method 119 Volhard's method 121 A modified
Gay-Lussac 123 Volhard's method applied to arsenic 124
GOLD--Detection 126 Amalgamation assay 126 Dry assay 127 (1) Size
of charges 127 (2) Sampling 127 (3) Assay tons 131 (4) Small buttons,
weighing 131 " " measuring 133 (5) Concentration in lead 136 Quartz
ores 136 Ores with oxide of iron 138 Ores with metallic sulphides 139
(6) Cyanide charges, residues, &c. 140 (7) Cupellation 142 Cupels 142
Cupellation temperature 143 Cupellation loss 145 (8) Inquartation 146
(9) Flatting 149 (10) Parting, in flasks 151 " in test tubes 152 " in
glazed crucibles 153 " Loss, &c. 154 (11) Check assays, surcharge 154
(12) Bullion assays in special apparatus 156 Silver, &c., in gold bullion
157 (13) Sampling of base bullion, &c. 157 CYANIDES--Commercial
cyanides 160 Double cyanides 161 Prussic acid 162 Gold-dissolving
power of cyanide liquor 162 Assay for cyanide strength 163, 165 Assay
of commercial cyanide 167 Alkalinity of cyanides 167 Acidity of ores
168 Metals in cyanide liquors 169 Cyanicides 169 PLATINUM 170
IRIDIUM 171 MERCURY 171 Dry assay 172 Wet method 173
CHAPTER X.

COPPER, LEAD, THALLIUM, BISMUTH, ANTIMONY.
COPPER--Introductory 175 Dry assay 176 Valuation of copper ores
181 Wet methods 183 (1) Electrolytic assay 184 Volumetric methods
194 (1) Cyanide method 194