John Almon.

The American journal of science and arts online

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or in glass cases with their own names paraded on ihe cards,
when most of the members of the Society have the new feeling
of a personal share in the ownership of the collections, when
the number of speK^imens received is blazoned forth as a matter
of pride and gratification, these incipient museums may have
considerable infiuence in stimulating collectors and observers of
nature. But after a time these collections outgrow the Society's
means, the specimens which may be required for study or com*
parison are encumbered by a mass of trash presented by persons
who do not know what else to do with it, or who have attadied
a false value to the fruits of their own labors, the permanent
officer can no longer have time to select for exhibition what is
worthy of it, nor to arrange those which might be available for
reference, and the Societv cannot afford to maintain the necessary
staff of keepers, even if they have a buildingr large enough for
the purpose. Packages and specimens are, nowever, still re-
ceived, exhibited at meetings to elicit formal thanks, and then
consigned to oblivion and decay in cupboards and garrets, the
members generally taking no further interest in what they can
make no use o£ If afterwards attention is called to this state
of things, it may be felt that something must be done ; the gra*
tuitous aid of patriotic members is called in, and the museum
may be more or less purged of trash and partially arranged.
But gratuitous aid, like voluntary subscriptions, is genenlly
given on the spur of the moment, and can never be depended
on for long continued and ever increasing demands ; the coUec>
tions relapse into a condition worse than the previous one, till
at last the Society is obliged to dispose of them as a clog on, in-
stead of an aid to, their operations. Such is the history of many
a museum I could name on the Continent and at home, including
our own, and such seems destined to be the career, on a large
scale, of the' Boston Society, notwithstanding its large invested
funds, if something is not done to give it a permanent indepen-
dence of individual disinterested efforts. It is now in the gratni-
tons aid period ; but when its present stores are doubled or quad-
rupled, when the thirteen or fourteen unpaid curators most not
only give their whole time to it, but require each of them one
or more assistants to do the work usefully, it will not be done at



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Anniversary meeting ef ike Linnean Society. 815

all ; and unless the Society .receives that extensive support which
can only be expected from the State, stowage, neglect, and de-
struction must ensue. It is no doubt considerations such as these
that have induced the Smithsonian Institution to repudiate the
burthen attempted to be imposed on them of a National Museum
which even the whole of tneir income would be insufficient to
maintain.

There is another class of museums which the Smithsonian
Institution appears to be promoting and assisting, with what re-
suits I have not sufficient means of judging; these are local
museums on a smaller scale in the smaller cities and provincial
towns. We have many such in Europe, both on the Continent
and in our own country, and if judiciousljr formed and ade-
quately maintained, ought to be very useful in encouraging the
taste K>r observation at home, and giving the scientific visitor
from a distance authentic information on the natural history of
the district. But too manjr of them depend on the fluctuating
support of voluntary contributions, and follow the fate of mu-
seums of societies. I have had occasion to go over many of
these local museums in various parts of the Continent and some
of our own, and it had been my intention to have collected infor*
mation, and in one of my addresses to have prefaced some gen-
eral observations on the subject, with a detailed review of all
our provincial Natural History museums and Associations ; but
so many of them are unfortunately more or less in a state of
collapse or uselessness, that I feared that special notes might be
invidious. I may perhaps be allowed, however, generally to re-
mark, that it appears to me that local provincial societies cannot
better apply their funds and influence than in the establishment,
on a permanent and independent footing, of a public museum,
confining their publications to matters of purely local interest,
which the general naturalist is not to be called upon to notice;
that this museum should aim at completeness in representing
the local district ; that exotic specimens should be restricted to
such a limited number of representative types or specimens for
comparison as their means will aflford, selected solely in propor-
tion to their utility in the museum, without reference to the indi-
viduality of the donor, or, if a certain number of complementary
specimens must be retained for a time in order to keep up the
public interest in the establishment, such specimens be unhesi-
tatingly expelled as soon as the cause for retaining them is gone.

In conclusion, I may perhapS be excused in alluding to some
general principles in the management of large museums, which
are inculcated by the Smithsonian Institution, more or less fol-
lowed on the Continent, formerly almost ignored with us, but
now more generally recognized. These are liberality of ex-
changes, fiacilities for study, and rejection of trash, principles



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816 T. Oaffield an the action of SunKght on Glass.

which it may be hoped are even gaining upon that most <
tially conservative establishment, our gigantic and, I might al*
most add, all-grasping British Museum. The larse sums annu-
ally voted for its support by the nation justify, indeed, not only
the exhibition on a most extensive scale of attractive specimens
for the occasional instruction or excitement to observation they
may give to the general public, but also the concession to the
popular party of a rare snow for the thousands of gazers who
would otnerwise congregate for less harmless amusements ; but
a large proportion of the support or contributions to the museum
is granted or given in the name of Science, and Science has a
right to its full share in the consequent benefit Whether Nat-
ural History be or not under the same roof as Art, Literature,
and Archaeology, Science has a claim upon Parliament to pro-
vide buildings and maintain a staff adequate to the scientific
arrangement of the collections ; and she has, I think, also a
right to call on the management, be they a composite Board of
Trustees or individual responsible heads, to reserve days, aooom-
modation, and specimens for examination and study, to allow of
the requisite appliances of light and heat in the process, to cause
the stores that nave accumulated for more than half a oentoiy
to be turned out of their hidden repositories, to have what is
useful to scientific researches renderea accessible for the purpose,
the surplus duplicates employed in a liberal system of exchanges,
with an eye quite as mucn directed to the distributing them use-
fully as to the pecuniary value of any expected return; and to
authorize the consigning to the dust-cart all absolute rubbish
occupying valuable space.



Art. XXSILL—The Action of Sunlight on Glass; by Thohas

Gaffield.

[Concluded from pafe 252.]

The comparative power of glass of different kinds to transmit
the actinic rays I have tested, by placing underneath pieces of
each kind, pieces of easily changing glass, (whito plate or Bel-
gian sheet glass,) exposing them one year, and notioing, at the
end of that period, the comparative depth of the yellow or
pink color to which the unaer pieces had chang^. The re-
sult of my experiments proved that the most easily transmis-
sive of the colorless glasses were the English crown, French
plate, two kinds of whito crystal sheet made in Massachu-
setts, (from the celebrated Berkshire white sand,) the New
Jersey sheet glass, one kind of English plate, and one kind
of Belgian sheet> and about in the order which I have named
them.



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T. OaffiM on the action of Suniighi on Olass. 817

Of the colored glasses, the blue transmitted the most, the pur-
ple less, the red and orange the leasts the glasses under these two
and the yellow and green showing little or no change.

This last experiment proves the propriety of the preference
given bj photographers to blue glass tor skylights, oecause it
transmits the blue rays, which exert the most actinic power.
But it may be added, that a colorless white glass, or bluish
white, — if one which will not change by sunlight to a yellow
or rose color, owing to the presence of manganese, or any other
cause, — is equally good, as it will transmit all the rays, and
among them^ the actinic or blue ones. In proportion as any
kind changes to a yellow or rose color, it will lose its power of
transmission, and its value as photographic glass. I have seen
specimens of the two kinds of white crystal sheet made in
Massachusetts, before alluded to, which answered the demands
of photographic artists. Of forei^ glass, I have noticed a fine
bluish white sheet, made lately without manganese, from a cer-
tain excellent manufactory in Belgium, and one kind of English
crown glass.

Should plate glass be required, the most permanentljr endu-
ring, or least likely to assume a yellow color, are a superior kind
of white plate, made by the French and Belgian Plate Glass
Companies, and an excellent quality of German crystal plate,
made at a long established factory in Hanover.

I desire to say here, however, that it is not the place where
any glass is made, which determines its good character, but the
actual constituent materials and the superiority of its manu-
facture.

Manu&cturers are frequently changing thei r mixture or ' ' batch, "
so that any results ^iven with one set of samples might differ
from those made with another set, from the same manufacturers.
For this reason, in noticing any differences which may occur in
experiments made by any of our readers, this fact should be
considered as an explaining cause.

I have seen specimens of glass from a factory which changed
to a yellowish tin^ in a few months, others which changed to a
purplish hue, and still others from the same factory, which
nardly changed at all. A difference in the mixture, (or batch,
as it is termed), makes a difference in the tinge of the specimens
from the same factory, both before and after exposure to sun-
light. The chief points for photographers are to get glass made
from as pure materials as possible, of as light a color as practi-
cable, and free from oxyd of manganese. A glass like either
of those named above, as most easily transmitting the actinic
rays, might be good for one year or more, and then become very
much injured for photographic effeotS| by the change of color to
yellow or pink by sunlight.



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318 T. Gafield on the action of SunUghi on Glass.

Any photographer can make these obsenrations practtoal, hj
testing the action of sanlight for six months or a year, on ul
the specimens offered him for sale. And all mannfactarere
can make them practical, by making their glass of pare mate-
rials, which will not have to be ^* doctored," to nse the glass-
makers' term for the use of manganese ; or by allowing the glass
to assume its natural color, even if it be a little blue or green,
rather than to run the risk of its subsequent change to yellow
or purple by exposure to sunlight

In the Gomptes Bendus for January 14th, 1867, Pelouze says,
(and we believe he is the first and only writer who has made
this observation) :

''Exposure to red heat deeolorizes the glasses which have
been made yellow by sunlight, or to speak more exactly, they
retake the light green shade which they had before exposure.
A second exposure to sunlight produces a second coloration,
similar to the first, and a red heat makes it disappear again*
These phenomena can be reproduced indefinitely. The glass
preserves its transparency ana does not give place to any 8tri»
or bubbles." He also says :

" I possess specimens of glass rendered violet by sonlight
All present the property of being decolorized by heat. A tem-
perature of 860 degrees is not sufficient. It is necessary to have
that employed in the reheating of glass in general, and that is
in the vicinity of red heat The glass decolorized by heat when
exposed to sunlight retakes the amethyst color which it acquired
the first time, loses it anew when it is heated ; and these curious
phenomena can be reproduced without cessation."

In confirmation of this most interesting statement of Pelouze,
I have exposed in a glass stainer's kiln, several spectmens of
glass which had been changed by the action of sunlight, some to
a yellow and some to a purple color. The exposure to an ex-
treme red heat made the glass assume, some a white, some a yel-
lowish white, and some a green color, which were probably the
original colors. These specimens were taken from windows
where they had been exposed from a few years to more than
half a century. Further experiments, which I have already
commenced, will show whetner we can reproduce the exact
original colors by heat, after being changed by exposure to aun-
light.

We have in the same kiln exposed some dozen original and
unexposed specimens of what are called colorless window glasses
of different kinds and shades of color, and found them on-
changed in the slightest degree by the action of great heat^ while
similar specimens have been changed in a few days, weeks or
months, by the simple action of the sun's rays. Fifteen meci*
mens of really colored glasses, (red, green, y^ow, &o.,) have



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T. GaffUld on the action of Sunlight on Olass. 319

been exposed in the same way without any change of color, ex-
cept a very slight one in a few specimens which were burnt or
over-heated.

In PoggendorfiTs Annalen, Berlin, of May 1st, 1889, is re-
corded the following interesting fact by A. Splittgerber :

'^ I would mention a curious fact, in which the sunbeams have,
if I may say so, done something in the art of penmanship ; not
only on the surface, but by inscribing characters through the
body of the glass ; and, though the matter is based upon causes
well known by experience, yet there has probably never before
been so striking an instance of their effect known. I am in
possession of a plate of glass which was used as a window
pane for more than twenty years, and on which was an inscrip-
tion in gold letters. This inscription was taken off by grinding
the plate on both sides, and polishing it so as to have a new
surface. When the glass had been polished, the inscription
could again be clearly seen. The parts which had been under
the letters remained white, while the remainder of the plate had
assumed a violet tint, in consequence of the manganese it con*
tained, a coloring which permeates the whole mass, as the grind-
ing of the surface prov«i. The uncovered part of the plate,
especially when laid upon a white background show the clearly
readable characters."

The same or a similar instance is related by Dr. Herman Yogfl
in the Photographische Mittheilungen, Berlin, of Sept., 1866.

Desiring to produce a similar result^ we made an inscription
on a piece of Belgian sheet glass, in part with gold and silver
leaf, and in part with black and white paint. The gold and
silver leaf were soon washed off, but the black and white painted
letters remained, and being removed afber an exposure or nearly
two years, the words stood out in clear contrast and full propor-
tions, the inscription being in the original color of the glass, and
the surrounding portions having been changed by the action of
the sunlight to a purple color.

A very interesting experiment can be made, to show the grad-
ually increasing effect of the sunlight on glass, b^r taking a piece
of easily changing glass, say 4x20 inches, painting black a
strip 4x2 inches at each end to preserve the original color, and
then exposing the strip to sunlight. At the end of one, two,
four, six, eight and ten months, one, two and three years respec-
tively, cover with black paint a strip 4x2 inches, and at the
end of three years remove all the paint, and you will have, in a
single piece of glass, the original color and all the gradations of
change effected by exposure from one to thirty -six months. I
have made a similar one with Belgian sheet glass exposed nearly
two years. It is one of those interesting experiments which
speak for themselves, and defy suspicion or contradiction.



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820 T. Gaffield an the action of Sunlight on Glass.

I have made an experiment for one year with two kiiids of
easily changing glass out of doors, and out of the direct rays of
the sun, and found that they were both slightly affected, and
changed toward a yellowish color. I did not expect any change,
but can, perhaps, properly account for it, on the ground that it
was the result of the action of diffused sunlight It is barely
possible that the sun may for a few minutes in some days of the
year have cast some reflections when I was not present, in the
dark corner in which I placed my specimens.

It may be, that the action of the sun's heat produced the
slight efrect noticed. If so, it would be an interesting oonfirma-
tion of Tyndall's experiments, and of his theory of the correla-
tion of forces. I do not consider my single experiment as en-
tirely conclusive, and shall make others, which will give us more
material for proper theories and conclusions.

The experiments which I have carried on for four years em-
brace one specimen of optical glass, a few kinds of flint glass
and glass ware ; sixteen kinds of French, Belgian, German and
English plate glass, four kinds of American, English, French
and Belgian rough plate, two of American and English crown
glass, ten kinds of American, Belgian, French and English
white sheet glass, four kinds of American, Belgian and Eng-
lish ordinary sheet glass, fifteen kinds and shades of English
colored glass, four of opaque, white enamelled and ground glass,
and one piece of the rough metal of American sheet glass ; in all,
about sixty varieties.

I have watched and recorded in some experiments, the results
from day to day, in others from month to month, and season to
season. I have now commenced a series, in which I may record
results from year to year, for ten years or more. In these, it
may be found that specimens of what are called colorless glasses
changed to a yellow color by exposure for a year, may by much
longer exposure be turned to a yellowish pink and a purple.
And some which have been entirely unaffected, may be affect^
by an exposure for ten or twenty years. Perhaps some of the
colored glasses may show signs of a change of hue or shade.

These new experiments include rough and polished plate,
crown, cylinder, ground, enamelled and colored glass, I have
also begun to expose under several of these kinds of glass^ pieces
of easily changing glass, which I shall take in from year to
year, these under pieces showing the power of these glasses
above them to transmit the actinic rays.

The most easily changing glasses are a certain kind of white
plate, which changes from a white to a yellowish color, and a
certain kind of Belgian sheet, which the manufacturers used to
make of a brownish yellow, (they now make it of a bluish or
greenish hue, and it is not so easily changed,) which changes U>



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T. Gafield on the action of Sunlighi on Glass. 821

a flesh color, or a pinkish hue. I have accordingly taken these
two kinds, for my under glass experiments. Under each of seve-
ral kinds, to be expos^ from one to ten or twenty years,
I have placed pieces 4x2 of the white plate. I shall take
in one piece at the end of the first, second, third, foarth, sixth
and tenth year. These six lights will show the increased action
of the transmitted rays firom year to year. By comparing the
different series with each other, one can perceive the comparative
actinic power of each kind of glass, or rather, their compara-
tive power of transmitting actinic rays.

Another interesting under experiment is the following. I have
placed under one piece of each kind of glass exposed, a piece
of easily changing glass, which I shall take in at the end of
the year.

At; the beginning respectively of the second, third^ fourth,
sixth and tenth years, I shall place under the same piece,
another strip of 4x2 inch glass, taking in each piece at the end
of the year of its exposure. This series will show the diminish*
ing or increasing power of the glasses under which they have
been exposed, to transmit the actinic rays ; in other words, will
show wnether exposure to the sun increases or diminishes the
actinic power of the glasses exposed, and renders them better or
worse for photographic purposes.

I have taken a piece of 4x 18, of easilv changing white plate,
painted with black paint two inches of each end, to preserve
the original color, and exposed the piece. At the end of the
year, I shall paint over two inches more of the glass. At the
end respectively of two, three, four, six, and ten years, I shall

f)aint over two inches more. At the end of tms time, or a
onger term, I shall remove all the black paint, and on one light,
I shall have all the grades of changed color and shade produced
b^ their different lengths of exposure. I shall lay aside one
piece of 4x18 white plate, taken from the same sheet with the'
exposed light, in order to compare the original with the changed
specimen.

I have painted and exposed, just inHhe same manner as above
described, a piece of 4 X 16 of easily changing Belgian sheet glass.

To show a speaking proof of the painting power of the sun-
light, I have taken a piece of 4x6 Belgian sneet and covered
it with a thin plate of brass, having the allowing letters cut out
of it: T. G., Jan. 1, 1867. I have taken another piece 4x6
Belgian, and stuck on with gum shellac the two letters T. G.
Afler exposure of one year or more, the removal of the brass
plate and letters will show in the former ease, rose or purple
colored letters on a brownish yellow ground, and in the latter,
brownish yellow letters on a rose or purple colored ground.

A similar experiment as the above, I have commenced with



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aS2 T. Oaffield on tk^ acHon of Sunlight on Glass.

two pieces of white plate, and the simple letters T. G., withoat the
date. The resalt ot the experimeDt m a year or more, will be to
show in one ease, yellowish letters on a light colored gronnd, and
in the other, light colored letters on a yellowish ground.

I have thus given, as briefly as possible, and yet as fully as
desirable, an account of my past and present experiments.
New ones are suggested from year to year. I trust that this in-
teresting field for observation and experiment may be worked
in other countries. There is ample room for research in the ap-
plication of chemical knowledge, of qualitative, quantitative,
and spectral analysis, and of photogenic tests, to discover the
exact action and causes of the interesting effects of the sun's
rays, which have here been noticed.

Theories, — The interesting phenomena of which I have given
an account^ have given rise to many theories to account for their
cause. Some attribute them to the presence of oxyd of iron,
and some to oxyd of manganese. Exactly how the change
takes place is a question on which writers differ, although it is
my opinion that the precise explanation can only be given after
a multiplication of experiments, and a thorough examination of
exposea and unexposed specimens of glass by quantitative and
quaUtative analysis, and perhaps bv spectral analysis and ob-
servation of photogenic effects, or photogenic tests.^

We will briefly state the part which the oxyds of iron and
manganese play in glass making. In almost all kinds of
window glass, and in some poorer qualities of flint glass, and
glass ware, materials are used which are not perfectlv and
chemically pure. The sand, the carbonate or sulphate of soda,
and the lime, one or all, contain' slight impurities of iron, the
protoxyd of which gives glass a green color.' To correct this,
afler the batch is partially melted, a little oxyd of manganese,
called glass-maJcer's soap, is put into the crucible or glass pot;
'some of the oxygen of the manganese flies off to the iron, and
converts the protoxyd into peroxyd of iron. The peroxyd



Online LibraryJohn AlmonThe American journal of science and arts → online text (page 88 of 102)