A TEXT-BOOK OF ASSAYING:
FOR THE USE OF THOSE CONNECTED WITH MINES.
BY
C. AND J. J. BERINGER.
REVISED BY
J. J. BERINGER,
ASSOC. OF THE ROYAL SCHOOL OF MINES; FELLOW OF THE CHEMICAL SOCIETY AND OF THE INST. OF CHEMISTRY; PRINCIPAL OF THE CAMBORNE MINING SCHOOL; AND LATE PUBLIC ANALYST FOR THE COUNTY OF CORNWALL.
With numerous Diagrams and Tables.
NINTH EDITION.
LONDON:
CHARLES GRIFFIN AND COMPANY, Limited,
EXETER STREET, STRAND.
1904.
[All rights reserved.]
PUBLISHER'S NOTE TO THE NINTH EDITION
The continued popularity of the present work, the last edition of which was published only a little over a year ago, continues to be a source of gratification to the publishers, who have much pleasure in issuing the present edition.
January 1904.
PREFACE TO THE SIXTH EDITION
The principal changes in this edition are additions to the articles on Gold, Cyanides, and Nickel, and a much enlarged Index. The additional matter covers more than forty pages.
J. J. BERINGER.
Camborne,
January 1900.
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.
A TEXT-BOOK OF ASSAYING.
CHAPTER I.
INTRODUCTORY.
Assaying has for its object the determination of the quantities of those constituents of a material which add to or detract from its value in the arts and manufactures. The methods of assaying are mainly those of analytical chemistry, and are limited by various practical considerations to the determination of the constituents of a small parcel, which is frequently only a few grains, and rarely more than a few ounces, in weight. From these determinations calculations are made, which have reference to a mass of material of, perhaps, hundreds of tons. But in all cases, whether the mass under consideration be large or small, whether the material be obtained by mining, grown, or manufactured, the assayer is supposed to receive a small quantity, called "the sample," which is, or ought to be, the exact counterpart of the mass of material that is being dealt with. The taking and making of this sample is termed "sampling"; and the men whose special work it is to select such samples are "the samplers."
But although "sampling" is thus distinct from "assaying," the assayer should be familiar with the principles of sampling, and rigorous in the application of these principles in the selecting, from the sample sent him, that smaller portion upon which he performs his operations.
Sampling.—In the case of gases, there is absolutely no trouble in mixing. The only difficulty is in drawing off a fair sample where, as in flues, the body of the gas is in motion, and varies a little in composition from time to time. In this case, care must be taken to draw off uniformly a sufficient volume of the gas during a prolonged period; any portion of this larger volume may then be taken for the analytical operation.
In the case of liquids, which mix more or less easily—and this class includes metals, &c., in the state of fusion—more or less severe agitation, followed by the immediate withdrawal of a portion, will yield a fairly representative sample.
In the case of solids, the whole mass must be crushed, and, if not already of fairly uniform quality, mixed, before sampling can take place. Most of the material which a sampler is called upon to deal with, is, however, in a more or less divided state and fairly uniform. In practice it is assumed that 5 per cent. of the whole (= 1/20th), if taken in portions of equal weight and at frequent and regular intervals, will represent the mass from which it was taken. Taking a heap of ore, A, and selecting one out of every twenty spade-, bag-, barrow-, or wagon-fuls, according to the quantity of stuff in the heap, there is obtained a second heap, B, containing one-twentieth of the stuff of
A = 1000 tons of rocks and lumpy ore.
B = 50 " " rough stones, 1/20th of A.
C = 2.5 " " small stones, 1/20th of B.
D = 0.125 " " coarse powder, 1/20th of C.