PAPERS FOR THOUGHTFUL BOYS. XII.-PRODUCTS OF SKILLED LABOUR.-GLASS. It LASS is one of the most beautiful inventions of man. ITS MANUFACTURE is very curious and interesting, for although glass is transparent, not one of the materials of which it is made partakes of that quality. One of the principal ingredients of all kinds of glass is silex, or flint, pieces of which are often seen on roads, or in thousands upon the seashore or beach. But these flints would be difficult to break, and glassmakers use, instead of them, sea-sand, which is flint already in powder. Other ingredients, such as lime, alumina, nitre, &c., are mixed in varying proportions according to the quality of glass required, some kinds being exquisitely pure and therefore expensive, while others are impure, coarse, and comparatively valueless. Sheet glass, used so largely for domestic purposes, for the glazing of window and conservatories, for mirrors and for picture-frames, is of three different kinds, each kind being manufactured by a different process. They are crown glass, plate glass, and what is called French plate. We must describe, as briefly as may be, the mode of manufacture in each case. Crown glass, which appears to be fast going out of use, is the worst kind of sheet glass made. It is familiar to most of us from the unsightly bull's-eye in the centre of its disc, and which used to be seen in the windows of sheds, kitchens, and workshops. It is made of fine white sand, kelp or burnt seaweeds containing soda and quicklime. These ingredients are melted in pots, placed in the midst of a strong coal-fire, within a kind of oven. When the mass is mixed it is taken out, cooled, picked over, and washed, it is then called frit. A certain quantity of old broken glass is next added to the frit, which is put in melting-pots, or crucibles, to be placed in the furnace. The furnace is a round-topped building terminating in a wide chimney, and is furnished with holes all round to put in and take out the pots. Within this furnace the frit in the pots is placed amidst strong flames, it is allowed to remain there until the dross rises to the top, when it is removed; the mass in the pot becomes clear, and the glass is made. The workman now dips one end of an iron pipe into a pot, and takes out glass enough in a lump to make a sheet. He then applies his mouth to the other end of the pipe, and blows the soft glass into the form of a globe; just as bubbles of soap and water are blown from a tobacco pipe. The globe is next taken from the pipe by another workman, upon an iron rod, to be flattened into a plate. The glass is now held upon the rod to one of the openings of the furnace until it has become hot. The workman then twirls the rod, slowly at first, and then more and more quickly, when the glass is also carried round upon the rod, until it spreads out and becomes a circular redhot table. This spreading of the glass round the rod may be compared to the circle which spreads round a stone let fall into a pond of water. The iron rod is then removed from the centre of the plate, and leaves a coarse thick lump, called the bull's-eye. The glass is then transferred to the annealing oven, in order that it may cool by slow degrees. This annealing process, which all manufactured glass undergoes, is necessary to give it toughness; were it not annealed, it would be so brittle as to break with the slightest handling. Plate glass is composed of fine white sand, soda, and lime, two metallic substances named manganese and cobalt, and fragments of good glass. These ingredients are mixed in due proportions, and having been cleansed of all impurities are carried to the furnace, where they are thrown into large crucibles formed of fire-clay. The crucibles, or pots, being thus charged, the doors of the furnace are shut, and a fierce fire, blown by a blast of hot air, is maintained for fourteen or fifteen hours, by which time the mixture is melted to a fluid state. The metal, as it is called, is now skimmed clear of its dross, and poured upon a hot copper-plate upon a table. As the glass spreads, all roughnesses are pressed out by passing a roller over it. It is rare, however, that the entire surface of a large casting is perfectly successful, and many of the plates have to be cut down in order to get rid of defects and flaws. This makes a large plate very expensive. After plate glass has been cast it has to be ground, smoothed, and polished. By these processes the rough plates of glass are brought to the brilliant state in which we are accustomed to see them. French plate is made by what is called the cylindrical process. In some of its features the process resembles that adopted in respect to crown glass; but others are wholly different. When the molten mass has been brought to a convenient shape, the workman blows a little air into it through the tube; the effect of the inflation is to give it a globular form; but what is wanted is a long cylinder and not a globe; to lengthen it and effect the desired transformation, he whirls the mass high above his head and swings it alternately in the deep pit beneath him. This process is continued until the metal has expanded into a cylinder over fifty inches in length, and perhaps twelve in diameter. The end of the blowpipe is then stopped, and through the expansion of the air within it, it bursts at the extremity. When the cylinder is sufficiently cool to be handled it is slit from end to end with a diamond. It is then carried to another furnace and exposed to intense heat. As soon as it shows signs of melting, the workman thrusts a long iron rod up the centre, and flattens it out on the slab; he then changes the rod for a kind of hoe-shaped instru ment, with which he kneads out the sheet to a perfect level, after which it is drawn away on the slab to the rear of the furnace, where it soon becomes sufficiently cool to be removed to the annealing oven. By a process similar to this the beautiful glass shades, which are now so common, and so useful for the preservation of delicate objects, are made. The glass vessels in domestic use are formed of flint glass, and are manufactured by blowing, being worked and moulded into shape by the aid of a few simple tools. Phials and bottles are now made in moulds. This is a more expeditious mode, and enables them to be made nearly of the same size. As most of our domestic glass is more or less ornamented by cutting, we must glance for a moment at the process. Glass intended to be cut, or ornamented, is made very thick, as the pattern is cut out from the surface. This is done by grinding the glass at small wheels of stone, metal, and wood. The iron wheels, with sand and water, are used for grinding away the substance of the glass; the stone wheel, with clean water, for smoothing the scratched surfaces; and the wooden wheel, with rotten stone and putty powder, for polishing. THE ORIGIN OF GLASS MANUFACTURE is uncertain. Josephus claims the discovery for the Israelites; Pliny assigns it to the Phoenicians, and states that the first glass-houses were erected in Tyre, where the only staple of the manufacture existed for many ages. Herodotus and Theophrastus likewise confirm the fact of the use of glass having been known in the earliest periods of civilisation, and of the establishment of glass-works in Egypt and Phoenicia, and even in India, where rock crystal was employed in its composition. The art of making glass is reputed to have been discovered by accident. Pliny states some Phoenician mariners, who had a cargo of nitrum (salt, or, as some have supposed, soda) on board, having landed on the banks of the Belus, a small stream running from the foot of Mount Carmel, and finding no stones to rest their pots on, placed under them some masses of nitrum, which, being fused by the heat with the sand of the shore, produced a liquid and transparent stream. Nor is the supposition unnatural; for the sand at this place was peculiarly well adapted for the making of glass. Strabo and Josephus alike supported the statement of Pliny, and it is probable that from this spot the material was obtained that was used in the glass-works of Tyre and Sidon. The process of glass manufacture as detailed by Pliny appears very much the same as that practised at the present. And Sir Gardiner Wilkinson in his work on "The Manners and Customs of the Ancient Egyptians" gives the representation of two glass blowers inflating a piece of molten metal by means of hollow tubes, taken from a painting at Beni Hassen, which was executed in the reign of a monarch who lived about 3500 years ago; and adds that glass vases, if we may trust to the Theban paintings, are frequently shown to be used for holding wine as early as the Exodus, about 1400 years before the Christian era. Winckelmann, a high authority, is of opinion that glass was employed more frequently in ancient than in modern times; it was used by the Egyptians, not only for drinking vessels, but for mosaic work, the figures of deities and sacred emblems, in which they attained excellent workmanship and surprising brilliancy of colour. They also made glass bugles and beads for necklaces, and a sort of network with which they covered the wrappers of mummies, so as to form by their various hues numerous devices and figures, resembling those that are made in our bead purses. Glass was used by the Egyptians for coffins, and in 1847 a process was patented in England for making coffins of glass. A pane of glass, and numerous fragments of broken glass bottles, were discovered on the excavation of the City of Pompeii. And Mr. Layard has found that the people of Nineveh had also acquired the art of making glass. There is in the British Museum a perfect and beautiful goblet which Mr. Layard excavated from among the ruins of Nineveh. It has a name engraved upon it, and from the characters employed, and the locality in which it was found, it is believed to be of date seven centuries before the Christian era, and probably the most ancient piece of manufactured glass in existence. In the reign of Tiberius glass-works were first established near Rome, and various sums were paid for vases or goblets. Glass was not only an article of luxury or ornament in the palaces, but employed to decorate altars and the tombs of the dead. Many fragments have been found in the catacombs, showing it to have been used likewise by the early Christians in their places of worship. The Greeks and Romans were adepts in the art of imitating precious stones by coloured glass. To use the words of Beckman: In the Museum Victorium, for example, there are shown a chrysolite and an emerald, both of which are so well executed that they are not only perfectly transparent and coloured throughout, but neither externally nor internally have the smallest blemish." The clear glass resembling crystal was exceedingly costly. Some idea of this may be gained from the statement that Nero gave for two cups of no extraordinary size, with two handles, 6000 sestertia, or nearly £50,000. There is a story told of an inyention by which glass was so far deprived of its brittle qualities, that when thrown down, the vessel composed of it would not break, but merely bruise, like metal. Whether the story is true or fabulous we are not in a position to say, but it is certain that experiments have recently been made in that direction, and no doubt many of my young readers will join with me in the earnest hope that such experiments will ultimately prove a success. OUR SUNDAY-SCHOOL ALBUM. BY ENOCH GRATTON. XXV.-MR. DANIEL NEVERFLINCH. E are now getting near to the end of our Album, but before we close it, I wish you to look at the pictures of three bright and happy faces; one is the face of a sweet and winning girl, another is the face ofa noble lad, and the other is the face of a sturdy and energetic man, who is here very fitly named Daniel Neverflinch, a real, solid, persevering friend to the school and to the church, a man with clear, cool head, loyal heart, and resolute will. There is a good deal of the old Roman soldier in this friend. He is not easily moved from the post of duty. Sneers may fall upon him as fast as snowflakes, but he does not flinch; waves of opposition may dash against him until they dash themselves into feeble spray, but he does not flinch; others may fall away and grow weary-Mr. Wavering may falter, Mr. Darkside may whine, Mr. Muchafraid may tremble, Mr. Tardy may loiterbut Mr. Neverflinch is undaunted to the end. When he moves, it is not with shambling foot; when he speaks, it is not with faltering tongue; there is fire on his lips, and firmness in his tread, and force in his conviction, and directness in his aim. He has stood by the school in all weathers, amid the rough blasts of winter and in the glowing heat of summer; when the school was weak and poor, and teachers were scarce, and difficulties were obstinate, and success was small. And he stands by it now it is strong, numerous, and eminently successful. I know of few schools which have prospered like the school for which Mr. Neverflinch cheerfully toils. He is not one of your jelly-like men who can be put into any shape, but who will not keep shape. He is not a reed shaken by the wind, or a shuttlecock to be batted and tossed by any hand. Others may twist and twirl, come and go, blow hot and cold, but Daniel is "steadfast and unmoveable." He has but little patience with temporisers and trimmers, and if they happen to cross his path he is likely to favour them with a few hard, biting words of reproof, and thus he gives offence to some. If he were only a little more cautious and mild and mealy-mouthed, he would escape a few troubles; but he would be far less honest and honoured and useful. He has been connected with the school from childhood; he has filled important offices, met with stern difficulties and subtle temptations, and when I saw him he was firm as a rock and as resolute as a lion. XXVI.-MASTER FRANK STERLING. Do any of my readers recognise the face and name of this truehearted lad? If they do they will readily admit that he is worthy of a place in our album, and that underneath the likeness we might fitly write these words: Tender, Trusty, and True. I know him |