A Textbook of Assaying | Page 3

(2) Iodide method 199 (3) Colorimetric
method 203 Examination of commercial copper 205 LEAD 211 Dry
assay 211 Wet assay 213 (1) Gravimetric method 213 (2) Volumetric
method 214 (3) Colorimetric method 218 THALLIUM 219 BISMUTH
220 Dry assay 221 Wet method 221 (1) Gravimetric determination 222
(2) Colorimetric assay 223 ANTIMONY 225 Dry assay 225 Wet
method 227 (1) Gravimetric assay 228 (2) Volumetric method 229
CHAPTER XI.
IRON, NICKEL, COBALT, ZINC, CADMIUM.
IRON 231 Gravimetric determination 233 Permanganate and
bichromate methods 234 Stannous chloride method 244 Colorimetric
determination 247 NICKEL 251 Dry assay 251 Electrolytic assay 254
Titration by cyanide 255 COBALT 259 ZINC 261 Gravimetric method
262 Volumetric method 263 Gasometric method 266 CADMIUM 269
CHAPTER XII.
TIN, TUNGSTEN, TITANIUM.
TIN 271 Vanning 273 Dry assay 276 Detection, &c. 279 Gravimetric
determination 281 Volumetric determination 282 Examples 284
TITANIUM 292 TUNGSTEN 295 NIOBIC AND TANTALIC
OXIDES 297
CHAPTER XIII.
MANGANESE, CHROMIUM, ETC.
MANGANESE 298 Gravimetric determination 300 Volumetric
determination 300 Ferrous sulphate assay 301 Iodine assay 302
Colorimetric determination 306 CHROMIUM 307 VANADIUM 310

MOLYBDENUM 311 URANIUM 312
CHAPTER XIV.
EARTHS, ALKALINE EARTHS, ALKALIES.
ALUMINA 314 THORIA 317 ZIRCONIA 317 CERIUM 318
LANTHANUM AND DIDYMIUM 319 YTTRIA 319 BERYLLIA
319 LIME 320 STRONTIA 324 BARYTA 326 MAGNESIA 328 THE
ALKALIES 330 SODIUM 334 POTASSIUM 336 LITHIUM 338
CÆSIUM 339 RUBIDIUM 340 AMMONIUM 340

PART III.

CHAPTER XV.
OXYGEN AND OXIDES--THE HALOGENS.
OXYGEN 344 OXIDES 345 WATER 350 THE HALOGENS 358
CHLORINE 359 BROMINE 361 IODINE 362 FLUORINE 363
CHAPTER XVI.
SULPHUR AND SULPHATES.
SULPHUR 367 Gravimetric determination 369 Volumetric
determination 370 SULPHATES 377 SELENIUM 379 TELLURIUM
379
CHAPTER XVII.
ARSENIC, PHOSPHORUS, NITROGEN.

ARSENIC 381 Gravimetric determination 383 Volumetric method,
"iodine" 384 " " "uranic acetate" 389 PHOSPHORUS 394 Gravimetric
determination 396 Volumetric determination 397 NITROGEN AND
NITRATES 400
CHAPTER XVIII.
SILICON, CARBON, BORON.
SILICON AND SILICATES 405 CARBON AND CARBONATES
414 COALS 418 SHALES 420 CARBONATES 424 BORON AND
BORATES 429
APPENDIX A.
Table of atomic weights and other constants 433 Table for converting
degrees of the centigrade thermometer into degrees of Fahrenheit's
scale 435 Tables showing strengths of aqueous solutions of nitric and
hydrochloric acids, of ammonia and of sulphuric acid 436
APPENDIX B.
Estimation of small quantities of gold 440 Practical notes on the iodide
process of copper assaying 441 Method of separating cobalt and nickel
442
APPENDIX C.
A lecture on the theory of sampling 444
INDEX 450

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.