Evening at Home 60

Evening at Home 60

Har._ O, yes. We call them fire-stones. When they are rubbed together

in the dark they send out great flashes of light, and have a particular

smell.

 

_Tut._ True. The proper name of these is _quartz_. It is found in large

quantities in the earth, and the ores of metals are often imbedded in

it. Sometimes it is perfectly transparent, and then it is called

_crystal_. Some of these crystals shoot into exact mathematical figures;

and because many salts do the same, and are also transparent, they are

called the _crystals_ of such or such a salt.

 

_Geo._ Is not fine glass called crystal, too?

 

_Tut._ It is called so by way of simile; thus we say of a thing, “It is

as clear as a crystal.” But the only true crystal is an earth of the

kind I have been describing. Well, now we come to _sand_; for this is

properly only quartz in a powdery state. If you examine the grains of

sand singly, or look at them with a magnifying glass, you will find them

all either entirely or partly transparent; and in some of the white

shining sands the grains are all little bright crystals.

 

_Har._ But most sand is broken or yellowish.

 

_Tut._ That is owing to some mixture generally of the metallic kind. I

believe I once told you that all sands were supposed to contain a small

portion of gold. It is more certain that many of them contain iron.

 

_Geo._ But what could have brought this quartz and crystal into powder,

so as to have produced all the sand in the world?

 

_Tut._ That is not very easy to determine. On the seashore, however, the

incessant rolling of the pebbles by the waves is enough in time to grind

them to powder; and there is reason to believe that the greatest part of

what is now dry land was once sea, which may account for the vast beds

of sand met with inland.

 

_Geo._ I have seen some stone so soft that one might crumble it between

one’s fingers, and then it seemed to turn to sand.

 

_Tut._ There are several of this kind, more or less solid, which are

chiefly composed of sand conglutinated by some natural cement. Such are

called _sandstone_, or _freestone_, and are used for various purposes,

in building, making grindstones, and the like, according to their

hardness.

 

_Har._ Pray, what are the common pebbles that the streets are paved

with? I am sure they strike fire enough with horses’ shoes.

 

_Tut._ They are stones of the siliceous kind, either pure or mixed with

other earths. One of the hardest and best for this purpose is called

_granite_, which is of various kinds and colours, but always consists of

grains of different siliceous stones cemented together. The streets of

London are paved with granite brought from Scotland. In some other

stones these bits of different earths dispersed through the cement are

so large as to look like plums in a pudding; whence they have obtained

the name of _pudding-stones_.

 

_Geo._ I think there is a kind of stones that you have not yet

mentioned—precious stones.

 

_Tut._ These, too, are mostly siliceous; but some even of the hardest

and most valuable are argillaceous in their nature, though possessing

none of the external properties of clay. The opaque and half-transparent

precious stones, such as jasper, agate, cornelian, and lapis lazuli, are

engraved upon for seal-stones; the more beautiful and transparent ones,

as ruby, emerald, sapphire, topaz, which go by the name of gems, are

generally only cut and polished, and worn in rings, ear-rings,

necklaces, and the like.

 

_Geo._ Diamond, no doubt, is one of them.

 

_Har._ So it has commonly been reckoned, and the purest of all; but late

experiments have shown, that though it is the hardest body in nature it

may be totally dispersed into vapour by a strong fire, so that

mineralogists will now hardly allow it to be a stone at all, but class

it among inflammable substances. The precious stones abovementioned owe

their colours chiefly to some metallic mixture. They are in general

extremely hard, so as to cut glass, and one another; but diamonds will

cut all the rest.

 

_Geo._ But are they not exceedingly rare?

 

_Tut._ Yes; and in this rarity consists the greatest part of their

value. They are, indeed, beautiful objects; but the figure they make in

proportion to their expense is so very small, that their high price may

be reckoned one of the principal follies among mankind. What proportion

can there possibly be between the real worth of a glittering stone as

big as a hazelnut, and a magnificent house and gardens, or a large tract

of country covered with noble woods and rich meadows and cornfields? And

as to the mere glitter, a large lustre of cut glass has an infinitely

greater effect on the eye than all the jewels of a foreign prince.

 

_Geo._ Will you please to tell us how glass is made?

 

_Tut._ Willingly. The base of it is, as I said before, some earth of the

siliceous class. Those commonly used are flint and sand. Flint is first

burnt or calcined, which makes it quite white, like enamel; and it is

then powdered. This is the material sometimes used for some very white

glasses; but sand is that commonly preferred, as being already in a

powdery form. The white crystalline sands are used for fine glass; the

brown or yellow for the common sort. As these earths will not melt of

themselves, the addition in making glass is somewhat that promotes their

fusion. Various things will do this; but what is generally used is an

alkaline salt, obtained from the ashes of burnt vegetables. Of this

there are several kinds, as potash, pearlash, barilla, and kelp. The

salt is mixed with the sand in a certain proportion, and the mixture

then exposed in earthen pots to a violent heat, till it is thoroughly

melted. The mass is then cooled till it is nearly of the consistence of

dough, and in this state it is fashioned by blowing and the use of

shears and other instruments. You must see this done some time, for it

is one of the most curious and pleasing of all manufactures; and it is

not possible to form an idea of the ease and dexterity with which glass

is wrought, without an actual view.

 

_Har._ I should like very much to see it, indeed.

 

_Geo._ Where is glass made in this country?

 

_Tut._ In many places. Some of the finest in London, but the coarser

kinds generally where coals are cheap; as at Newcastle and its

neighbourhood, in Lancashire, at Stourbridge, Bristol, and in South

Wales. I should have told you, however, that in our finest and most

brilliant glass, a quantity of the oxide of lead is put, which vitrifies

with the other ingredients, and gives the glass more firmness and

density. The blue, yellow, and red glasses are coloured with the oxides

of other metals. As to the common green glass, it is made with an alkali

that has a good deal of calcareous earth remaining with the ashes of the

plant. But to understand all the different circumstances of glassmaking,

one must have a thorough knowledge of chymistry.

 

_Geo._ I think making of glass is one of the finest inventions of human

skill.

 

_Tut._ It is perhaps not of that capital importance that some other arts

possess; but it has been a great addition to the comfort and pleasure of

life in many ways. Nothing makes such clean and agreeable vessels as

glass, which has the quality of not being corroded by any kind of

liquor, as well as that of showing its contents by its transparency.

Hence it is greatly preferable to the most precious metals for drinking

out of; and for the same reasons it is preferred to every other material

for chymical utensils, where the heat to be employed is not strong

enough to melt it.

 

_Har._ Then glass windows.

 

_Tut._ Ay; that is a very material comfort in a climate like ours, where

we so often wish to let in the light, and keep out the cold wind and

rain. What could be more gloomy than to sit in the dark, or with no

other light than came in through small holes covered with oiled paper or

bladder unable to see anything passing without doors! Yet this must have

been the case with the most sumptuous palaces before the invention of

window-glass, which was a good deal later than that of bottles and

drinking-glasses.

 

_Har._ I think looking-glasses are very beautiful.

 

_Tut._ They are, indeed, very elegant pieces of furniture, and very

costly too. The art of casting glass into large plates, big enough to

reach almost from the bottom to the top of a room, is but lately

introduced into this country from France. But the most splendid and

brilliant manner of employing glass is in lustres and chandeliers, hung

around with drops cut so as to reflect the light with all the colours of

the rainbow. Some of the shops in London, filled with these articles,

appear to realize all the wonders of an enchanted palace in the Arabian

Nights’ Entertainments

 

_Geo._ But are not spectacles and spying-glasses more useful than all

these?

 

_Tut._ I did not mean to pass them over, I assure you. By the curious

invention of optical glasses of various kinds, not only the natural

defects of the sight have been remedied, and old age has been in some

measure lightened of one of its calamities, but the sense of seeing has

been wonderfully extended. The telescope has brought distant objects

within our view, while the microscope has given us a clear survey of

near objects too minute for our unassisted eyes. By means of both, some

of the brightest discoveries of the modern times have been made; so that

glass has proved not less admirable in promoting science than in

contributing to splendour and convenience. Well—I don’t know that I have

anything more at present to say relative to the class of earths. We have

gone through the principal circumstances belonging to their three great

divisions, the _calcareous_, _argillaceous_, and _siliceous_. You will

remember, however, that most of the earths and stones offered by nature

are not in any one of these kinds perfectly pure, but contain a mixture

of one or both the others. There is not a pebble that you can pick up,

which would not exercise the skill of a mineralogist fully to ascertain

its properties, and the materials of its composition. So inexhaustible

is nature!

 

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