Chapter I: Preface

The Text-book now offered to the public has been prepared to meet the existing want of a practical "handy book" for the Assayer.

To mining men the word "assaying" conveys a sufficiently clear meaning, but it is difficult to define. Some writers limit it to the determination of silver and gold, and others imagine that it has only to do with "furnace-work." These limitations are not recognised in practice. In fact, assaying is becoming wider in its scope, and the distinction between "assayers" and "analysts" will in time be difficult to detect. We have endeavoured rather to give what will be of use to the assayer than to cover the ground within the limits of a faulty definition.

At first our intention was to supply a description of those substances only which have a commercial value, but on consideration we have added short accounts of the rarer elements, since they are frequently met with, and occasionally affect the accuracy of an assay.

Under the more important methods we have given the results of a series of experiments showing the effect of varying conditions on the accuracy of the process. Such experiments are often made by assayers, but seldom recorded. Statements like those generally made--that "this or that substance interferes"--are insufficient. It is necessary to know under what conditions and to what extent.

Students learning any particular process cannot do better than repeat such a series of experiments. By this means they will, at the same time, acquire the skill necessary for performing an assay and a confidence in their results based upon work under different conditions.

The electrolytic method of copper assaying given under _Copper_ is a modification of Luckow's; it was introduced by us into the offices of the Rio 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.