Burning glass

“ I think we need not give many reasons to show that a man could not live there long. Every boy knows how a burning glass can kindle a piece of paper by concentrating the sun's rays. Some great burning glasses have been constructed with which iron, steel, and even flints have been actually melted by the sun's heat. It can be proved that the sun himself must be hotter than any temperature that can be produced in the focus of the most powerful burning glass. ”

“ If we saw that the burning-glass was porous and that the light filtered through the apertures, it would be clear why it burns, because we should see the phenomenon occur in every separate glass; but we should yet have to form the abstract idea that this quality is universally true of every possible glass. ”

“ Another experiment with the burning-glass will also teach us something. Take a candle, and from its flame you can get a bright point at the focus. It may fall upon your hand, but you can hardly feel it, and you will readily believe that the focus is not nearly so hot as the candle. Even when a burning-glass is held in front of a bright fire there is comparatively little heat in the focus. By using a lens to condense the beams from an electric lamp, Professor Tyndall has shown how to light a piece of paper, and to produce many other effects. ”

“ Unless it has fresh air, it cannot burn. There is something—a gas—in the air that makes the flame burn, and when it has used up all this gas inside the glass, and can’t get any more, it stops burning. ”

“ If therefore there be in any thing any good, which being burnt in the fire is by fusion or melting, turned into transparent glass, it doth manifest it self in its utmost or ultimate essence, and shine forth in its brightness, insomuch that every one may see what lay hidden in its life afore thus burning it. For example, I take wood, an herb, or an animal, I burn it and transmute it into ashes; these ashes I melt and turn into glass. Having thus done, there appears no colour visible, for the glass is white, and that because the sulphur is consumed in the burning ”

“ Although very convenient in use, it has the disadvantage of being rather too highly inflammable and capable of burning without a wick, thus involving a certain fire risk; the flame is scarcely visible in a bright light, and the heat given by either the ordinary flame or the blowpipe flame produced from alcohol is considerably less than that from a similar flame in which coal gas is used. For small work, however, the facility with which a spirit lamp may be lighted may more than counterbalance these disadvantages at times. ”

“ A convex lens fashioned from ice by means of a sharp-edged stone and finally shaped by melting the surfaces as they are rubbed in the palms of the hands, will kindle a fire in highly inflammable material if the sun is high and the atmosphere is fairly clear. Burning-glasses are used to a considerable extent at the present time in certain countries and it is reported that British soldiers were supplied with them during the Boer War. ”

“ This is the case, when wax candles, tallow candles, chips of wood, spirit of wine, ether, and every other substance which I have yet tried, except brimstone, is burned in a close glass vessel, standing in lime-water. This precipitation of fixed air (if this be the case) may be owing to something emitted from the burning bodies, which has a stronger affinity with the other constituent parts of the atmosphere [3] . ”

“ The largest drinking-glass holds but half a pint, so that your diving light soon goes out for the want of air. A burning candle consumes as much air as a man, and he requires nearly a gallon of air every minute, so that, according to the size of the glass over the flame, you can calculate how many seconds it will remain alight, a large flame requiring more air than a small one. A quart bell-glass is very useful. A substitute is easily made from a green glass pickle bottle, with the bottom cut off. ”

“ A most convincing proof that glass transmits the rays of the sun without being heated by them is afforded by the burning lens, which by converging the rays to a focus will set combustible bodies on fire, without its own temperature being raised. ”

“ In the case of a blowpipe burning oil or wax fuel the flame may be a trifle more ragged without disadvantage.
Bellows and Blowing.—The bellows should be adjusted to deliver air at constant pressure, either by insertion of a tap or, better, by attention to the wind reservoir if necessary. The movement of the foot in blowing should be steady, not jerky.
Heating Glass.—The tube or rod should be heated cautiously until it has reached its softening point in its thickest part. Steady rotation of the glass during the heating is almost essential. ”

“ Some ignited bodies are found to be much warmer than some flames; for instance, red hot iron is much warmer, and burns more than the flame of spirits of wine. 26. Some bodies even not ignited, but only heated by the fire, as boiling water, and the air confined in reverberatories, surpass in heat many flames and ignited substances. 27. Motion increases heat, [96] as is shown in the bellows [142] and the blowpipe; for the harder metals are not dissolved or melted by steady quiet fire, without the aid of the blowpipe. 28. Let an experiment be made with burning-glasses ”

“ In the frantic hurry and agitation of the moment, it never struck me that I might let out the flame instead of letting in the air. I struck at the skylight, and battered in the cracked, loosened glass at a blow. The fire leaped out like a wild beast from its lair. ”

“ As this roaring flame contains a great quantity of carburetted hydrogen, and even of vapour of oil, escaped from combustion, it possesses a disoxidizing or reducing property in a very high degree.
PLACES FIT TO WORK IN.
Every place is adapted for a workshop, provided it is not too light and the air is tranquil. The light of the lamp enables one to work with more safety than day-light, which does not permit the dull-red colour of hot glass to be seen. Currents of cold air are to be avoided, because they occasion the fracture of glass exposed to them on coming out of the flame. ”

“ And though it is possible, with care, to employ the hot space immediately in front of the visible end of an ordinary brush flame, which is rich in air, yet, in practice, it will not be found convenient to heat large masses of lead glass nor tubes of large size, to a sufficiently high temperature to get the glass into good condition for blowing, by presenting them to the common brush flame. ”

“ I had not dreamed the rattling of glass, nor the jarring sensation, nor yet the smoke and heat and lurid light. The walls shook with a dull vibration, and the window-panes were like castanets. Through the glass transom over the door I could see a shimmering, ruddy glow that rose and fell, and was brightened by bursting sparks and little darting tongues of yellow flame. Apart from this one lurid spot all was thickly curtained into darkness by a heavy pall of smoke. ”

“ This glass, though formed in the vast crucibles of the mountains at the time of their combustion, might become very useful in the arts; for being already completely manufactured by the hand of nature, it would only require to be exposed to the action of the fire in order to fuse it anew, and render it susceptible of being moulded into all the forms that the hand of man is able to give to it. ”

“ When radiant heat is allowed to pass through glass, the latter substance is not found to be transparent to heat rays as it is to those of light, but a considerable proportion of heat is arrested and stopped; consequently glass fire-screens are to be found in the mansions of the wealthy, because they obstruct the heat but do not exclude the cheerful light and blaze of the fireside. ”

“ If at any time the glass shows indications of collapsing, it must be removed from the flame and gently blown into shape, during which operation it may be rotated in the perpendicular position; indeed, to promote a regular distribution of the glass by allowing it plenty of time to collect, it is well from time to time to remove the heated mass of glass from the flame, and slightly expand it by blowing. ”

“ And now through the icy glass which held the humans rigid, two shapes of coiling flame turned lazily over and over—one shape supporting a human body and glowing incandescent with malevolence, the other still too amazed for emotion, but stretching its new limbs of fire with a sort of reluctant, voluptuous luxury as the endless ribbon rolled in convolutions of flame in and out of its own length. ”

“ Sometimes several plates of glass are laid over each other with a layer of dry pulverulent lime between each. The fire is now lighted, and most gradually raised, lest the glass should be broken; and after it has attained to its full heat, it must be kept up for 3 or 4 hours, more or less, according to the indications of the trial slips; the yellow colour being principally watched, as it is found to be the best criterion of the state of the others. When the colours are properly burnt in, the fire is suffered to die away, so as to anneal the glass. ”

“ That it is rarely safe to blow glass whilst it is still in the flame, except in certain special cases that will be mentioned subsequently. Therefore always remove apparatus from the flame before blowing. ”

“ Because that force is believed, in our times just as in former times, to attract the liquor of glass to itself, as it attracts iron to itself, purges it when drawn, and makes clear glass from green or muddy; but the fire afterwards burns up the loadstone. ”

“ Abe said, "a German soldier don't need to be a gentleman at all, because when it comes to stealing château furniture, destroying cathedrals, burning houses, and chopping down fruit-trees, any experience as a gentleman wouldn't be much of a help to a German soldier."
"That's what I am telling you, Abe," Morris declared. "Germany has made war a business, y'understand, and she figures that a gentleman in the war business is like a gentleman in the pants business. ”

“ It unites the advantages of not fatiguing the workman, of leaving his hands free, and of rendering him absolute master of the current of air, which he can direct on the flame either of the lamp or the candle,—advantages which are not offered in the same degree even by the table of the glass-blower. ”

“ Next to olive oil and wax, it affords the greatest heat, and the least smoke. But, in a word, as in the working of glass, the operator has more need of a bright flame without smoke, than of a high temperature, any combustible may be employed which is capable of furnishing a flame possessing these two qualities. The vegetable oils thicken, and suffer alterations more or less sensible, when they are long exposed to the action of the air. ”

“ As a rule I have observed that beginners are apt to raise their glass to a higher temperature than is necessary, and that they employ larger [23] flames than are wanted. If glass be made too soft it may fall so completely out of shape as to become unworkable except in very skilful hands. The following rules, therefore, should be strictly adhered to. Always employ in the first instance the smallest flame that is likely to do the work required. In operations involving blowing out viscous glass, attempt to blow the glass at low temperatures before higher ones are tried. ”

“ The flame of a lamp, or candle, condensed and directed by a current of air, is exceedingly useful in a great number of arts. The instrument which is employed to modify flame is the Blowpipe. This is an indispensable agent for jewellers, watch-makers, enamellers, glass-blowers, natural philosophers, chemists, mineralogists, and, indeed, for all persons who are occupied with the sciences, or their application to the arts. Its employment offers immense advantages in a multitude of circumstances ”

“ Applying the candle in this manner several times, the effect will always be the same; and sometimes the fire will fill the whole body of the glass, and even circulate to the bottom of the liquor; at others, it will only reach a little down its neck. The great caution to be used in making this experiment, is the making the vapour of a proper heat; for if made too cold few vapours will arise; and, if made too hot, they will arise too fast, and will only take fire in the neck of the glass, without any remarkable coruscation. ”

“ It seems never to have occurred to the makers of these things that the gas flames inside the globes are always wider than the openings beneath them, through which the air required for combustion passes; and that, as a rule, the light of the flame is required to be cast downward. Gas flames always flicker in these old-fashioned glasses, because the sharp current of entering air blows them about. And the light cannot come downward because of the metal ring and its arms, and the glass, which is always thicker and generally dingier at this part of the globe. ”

“ He can therefore easily work upon very large masses of glass. In a special case, such a source of heat might be devised by the amateur. Usually, however, the difficulty may be overcome without special apparatus. It is, in fact, only necessary to carry out the instructions given below to obtain a considerable brush flame rich in air, in which the lead glass can be worked, not only without discoloration, but with the greatest facility. ”

“ In general, large pieces of glass should be heated very slowly in the smoky flame, and the larger the diameter of the tube the greater the length which must be kept warm to prevent cracking. All large pieces should be carefully heated over their whole circumference to the point where the soot deposit burns off, before being finally cooled. After being thus heated they are cooled in a large smoky flame until well coated with soot, then the flame is gradually reduced in size and the object finally cooled in the hot air above it until it will not set fire to cotton. ”