Transcriber’s Note
In the Plain Text version of this eBook, superscripts are indicated by
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from italics.
The “Westminster” Series
GLASS MANUFACTURE
GLASS
MANUFACTURE
BY
WALTER ROSENHAIN B.A. B.C.E.
SUPERINTENDENT OF THE DEPARTMENT OF METALLURGY AND
METALLURGICAL CHEMISTRY AT THE NATIONAL
PHYSICAL LABORATORY
[Illustration]
NEW YORK
D. VAN NOSTRAND COMPANY
23 MURRAY AND 27 WARREN STREETS
1908
BRADBURY, AGNEW, & CO. LD., PRINTERS,
LONDON AND TONBRIDGE.
PREFACE
The present volume on Glass Manufacture has been written chiefly for
the benefit of those who are users of glass, and therefore makes
no claim to be an adequate guide or help to those engaged in glass
manufacture itself. For this reason the account of manufacturing
processes has been kept as non-technical as possible; no detailed
drawings of plant or appliances have been given, and only a few
illustrative diagrams have been introduced for the purpose of avoiding
lengthy verbal descriptions. In describing each process the object
in view has been to give an insight into the rationale of each
step, so far as it is known or understood, and thus to indicate the
possibilities and limitations of the process and of its resulting
products rather than to provide a detailed guide to the technique of
the various operations. The practical aim of the book has further been
safeguarded by the fact that the processes described in these pages
are, with the exception of those described as obsolete, to the author’s
definite knowledge, in commercial use at the present time. For this
reason many apparently ingenious and beautiful processes described in
earlier books on glass have not been mentioned here, since the author
could find no trace of their employment beyond the records of the
various patents involved. On the other hand the reader must be warned
to bear in mind that the peculiar conditions of the glass manufacturing
industry have led to the practice on the part of manufacturers of
keeping their processes as secret as possible, so that the task of the
author who would give an accurate account of the best modern processes
used in any given department of the industry is beset with great
difficulties. The author has endeavoured to steer the best course open
to him under these circumstances, and he would appeal to the paucity of
glass literature in the English language as evidence of the difficulty
to which he refers.
In addition to these difficulties, which arise largely from
considerations of a commercial nature, the writer of a book on glass
is further confronted with technical difficulties of no inconsiderable
order. As already indicated, the aim of the present author has been to
describe processes from the point of view of principles and methods
rather than as mere rule-of-thumb descriptions of manufacturing
manipulations, but in doing this he is met at every turn by the fact
that from the scientific side the greater part of the field of glass
manufacture is a “terra incognita.” In making this statement the
labours of many eminent scientific workers are by no means forgotten,
but the entire field is so large and beset with such great experimental
difficulties that even the labours of a list of investigators that
includes the names of Fraunhofer and Faraday, Stokes, Hopkinson, Abbé
and Schott, have resulted in little more than an accumulation of
empirical data which, while they have been productive of great direct
practical results, have left the science of glass still in a very
elementary condition. To take two examples in illustration of this
fact we may mention the question of the connection between chemical
composition and any of the physical properties of glass, such as
refraction and dispersion of light, and on the more mechanical side the
question why all processes, such as rolling or moulding, which involve
the contact of hot glass with metal result in a roughening of the
glass surface. The former question has been studied by several of the
investigators named above, Schott and Abbé having particularly devoted
an enormous amount of labour and money to the study of the question
with results which have proved disappointing from the scientific point
of view. By prolonged experimenting and the employment of a costly
system of trial and error an important series of novel and useful
glasses has been produced by these workers, but no law by whose aid the
optical properties of a glass of given chemical composition could be
predicted has yet been discovered, and as a summary of the known facts
only the vaguest general principles are available for the guidance
of those who wish to produce glasses of definite properties. The
same applies in a similar degree to most of the other properties of
glass, with the exception, perhaps, of density and thermal expansion;
attempts to generalise from the known data of a limited number of
glasses generally meet with unqualified failure. The conclusion which
one is forced to admit is that the fundamental principles underlying
the nature and constitution of glasses have yet to be discovered.
A study of the other question mentioned above as an example of the
limitations of our knowledge leads to the same conclusion; an almost
endless succession of inventors have busied themselves with devices
for overcoming the roughening action of rollers and moulds upon
glass, but without any real success. A long list of other examples
of the same kind could be given, our knowledge of the physical and
chemical principles underlying many of the phenomena met with in glass
manufacture being deplorably deficient. It will thus be seen that to
write a truly scientific account of glass manufacture is at the present
time impossible, and the reader is asked to bear this in mind if he
should find the chemical or physical explanations given in this book
less frequent or less adequate than could be desired.
Having dwelt somewhat emphatically on the limitations of our present
scientific knowledge as applied to glass manufacture, it is perhaps
scarcely necessary at the present time to emphasise the fact that this
state of affairs should act as the strongest incentive to further
investigation of the whole subject. The difficulty, however, lies
in the fact that such investigation can scarcely be carried on by
voluntary workers in ordinary laboratories, but must be undertaken
with the active help of glass manufacturers at their works. Glass is
essentially a substance that cannot be satisfactorily handled in small
quantities, particularly so far as all the phenomena connected with its
production and manipulation while hot are concerned; the influences
of containing vessels, of furnace gases and of rapid cooling are all
enormously exaggerated if ounces instead of hundredweights or tons of
glass are used for experimental purposes, and these influences and
others of the same nature vitally affect all the results of small-scale
laboratory operations. The progress of our scientific knowledge of
glass--and the consequent development of the glass industry from its
present state where rule-of-thumb and “practical experience” still hold
excessive sway--lies in the hands of those concerned in the industry
itself. It must be admitted that to undertake such work involves the
expenditure of much time and money on the part of a manufacturer, while
the field is so large and the problems so complicated that any adequate
return cannot be promised for the _immediate_ future; on the other
hand the very size of the field and the difficulty of the problems
offers the promise of the greatest ultimate reward; a really important
scientific discovery in connection with glass would be certain to bring
in its train industrial developments whose limits it is impossible to
foresee. The industrial success of the glass-works of Schott in Jena
is often quoted as a brilliant example of commercial success resulting
from purely scientific investigations in this actual field; an
example of still greater magnitude is furnished by the success of the
aniline dye works of Germany which are built up on purely scientific
achievements. The glass industry as a whole, supplying some of the
absolute necessaries of modern life, should be capable of offering the
greatest rewards to success, and the example of other industries has
shown that _ultimate_ success is bound to reward properly-conducted and
perseverant scientific research. Nowhere is this more urgently needed
than in the whole field of glass manufacture.
The author is indebted to Mr. W. C. Hancock for valuable assistance in
the reading of proofs and various suggestions in connection with the
contents of this book.
TABLE OF CONTENTS
PAGE
PREFACE v
CHAPTER I.
THE PHYSICAL AND CHEMICAL PROPERTIES OF GLASS.
Definition of the term “Glass”--Amorphous structure the
common feature of all vitreous bodies--Glass a congealed
fluid--Glasses not definite chemical compounds but
complex solutions--Range of chemical composition
available for glass-making--Considerations governing
chemical composition--Influence of composition on
physical properties--Chemical stability of glass--
Permanence of glass surfaces--Action of water, acids,
and alkalies on glass--Action of light on glass _p._ 1