Melting pot

“ The melting pots (fig. 738.) are made of cast iron, and hold conveniently 400 pounds of metal. They are furnished with a spout or lip for pouring out the metal, and with two ears, on which the tongs of the crane lay hold in lifting them out of the furnace. The pot rests on pedestals on the grate of the furnace, and has a ring cast on its edge to prevent the fuel falling into it. Whenever it becomes red hot, the metal properly prepared and mixed, so as to produce an alloy containing 0·915 parts of gold, is put in, and during the melting, which occupies some hours, it is occasionally stirred. ”

“ In starting with an empty melting pot, turn oil the heat before putting in any lead, and let the pot become thoroughly heated in order to drive off any moisture. With the pot thoroughly hot, drop in the lead, which must also be dry. When the metal has become soft enough to stir with a clean pine stick, skim off the dirt and dross which collects on top and continue heating the lead until it is slightly yellow oil top. Dirt and lead do not mix, and the dirt rises to the top of the metal where it may readily be skimmed off. ”

“ NEW YORK is not merely a melting pot for the poor and the humble of the lands of the earth. In its capacious depths, unknown and unsuspected, float atoms of an entirely different sort: human beings with the blood of the high-born and lofty in their veins, derelicts swept up by the varying winds of adversity, adventure, injustice, lawlessness, fear and independence. ”

“ A country cast suddenly into the melting-pot,—say into the Medea's-Caldron; to be boiled into horrid dissolution; whether into new youth, into sound healthy life, or into eternal death and annihilation, one does not yet know! ”

“ The production of a melting of optical glass begins with a very gradual heating of the pot to a bright red heat in one of the kilns. It is then transferred to its furnace which has been brought to a similar temperature, sealed in by slabs of firebrick, leaving its mouth easy of access, and then the heat is pushed up to near the melting temperature of the mixture in production, which varies over a rather wide range, from a moderate white heat to the utmost that a regenerative gas furnace can conveniently produce. ”

“ But yet they will let it stand, perhaps half an hour longer or more, according as they guess [Pg 167] the Fire to be Hotter or Cooler, that they may be the more assured it is all throughly Melted. And when it is Melted the Melting Pot will not be a quarter full.
And in or against that time they make another small Furnance close to the first, (to set an Iron-Pot in, in which they Melt Lead) on that side from whence the Wind blows; Because the Person that Lades the Lead out of the Iron-Pot (as shall be shewed by and by) may be the less annoyed with the Fumes of the Mettal, in both Furnances. ”

“ First, as regards the melting process, although the tank-furnace has almost entirely superseded the pot furnace for the production of ordinary sheet-glass, there are still some special circumstances under which the pot furnace is capable of holding its own. Thus, where for special purposes it is desired to produce a variety of sheet-glass which, as regards all defects arising out of the glass itself, and especially as regards colour, is required to be as perfect as possible, melting in pots is found advantageous, and for some very special purposes even covered (hooded) pots are used. ”

“ In the tank furnaces the production is substantially continuous, the active melting taking place at one end, where the materials are introduced, while the clear molten glass flows to the cooler end of the tank or to a cooler compartment, whence it is withdrawn for working.
The ordinary method of making optical glass is by a modification of the pot process, each pot being fired separately to permit better regulation of the temperature. ”

“ Where smaller special casting-pots are used, these are not exposed to such prolonged heat in the furnace, and are never exposed to the chemical action of the raw materials, so that these subsidiary pots may perhaps be made of a material better adapted to withstand sudden changes of temperature than the high-class fire-clay which must be used in the construction of melting pots. On the other hand, the transference of the glass from the melting to the casting-pots involves a laborious operation of ladling and the refining of the glass, with its attendant expenditure of time and fuel. ”

“ Such enforced idleness of a melting furnace is of course very undesirable from an economical point of view, and it is generally avoided by adopting the alternative234 method of drawing the pot bodily out of the furnace as soon as the stirring operation is ended. ”

“ The pot melts at one operation sufficient silver to make a bar of two hundred and fifty marks, or one hundred and twenty-five pounds. Alternate layers of piña and charcoal are put in the smelting pot; fire is applied, and air furnished by a rude bellows. When the silver is melted, the pot is turned on its arms, and the silver poured out of a sort of ear at the top of the pot into an iron mould below. ”

“ The fire which is hot enough to melt a lump of ice may not be hot enough to melt an iron poker; on the other hand, it may be sufficiently hot to melt a tin spoon. Different substances melt, or liquefy, at different temperatures; for example, ice melts at 0° C., and tin at 233° C., while iron requires the relatively high temperature of 1200° C. Most substances have a definite melting or freezing point which never changes so long as the surrounding conditions remain the same. ”

“ The man in charge of melting uses a bath thermometer constantly and regulates the temperature of the water in the jacket by the admittance of cold water to chill it or steam to warm it so that the temperature of the melting oil does not exceed 156° F. It usually takes 11⁄2 hours to properly melt the contents of a full kettle. When the melting is complete the stirrer is raised out of the oil and allowed to remain raised while the oil is settled. ”

“ The series I have used consist of tin, melting about 440° F.; bismuth at about 510° F.; lead at about 612° F.; and nitrate of potash at about 660° F. A straight piece of iron wire, passing through the side of the furnace to the bottom of each of the holes, enables the workmen to feel which of the substances are melted, and to regulate the fire accordingly. It is important, for the quickness and perfection of the decomposition, that the oil and water, during their entire passage through the heating tubes, should remain in the same state of intimate mixture in which they enter them. ”

“ A mixture of sand with a solution of caustic potash or soda is introduced into an iron boiler, under 5 or 6 atmospheres of pressure, and heated for a few hours. The iron boiler contains an agitator, which is occasionally operated during the melting. ”

“ Then, after mixing, 100 to 200 grams of it are carefully weighed and placed in a hot crucible, the heat of which should be sufficient to melt all the lead. The molten lead should not be overheated and should show no loss due to the melting. The removal of the oil may have decreased the weight by perhaps one half per cent. If the lead gives dross on heating it may be melted under 10 or 20 grams of potassium cyanide, which prevents the formation of dross. ”

“ More rapid and thorough roasting is effected, since the presence of the inert flux prevents clotting or undue sintering of the sulphides in the roaster. (iv.) The charge is found to be in a much better condition, both physically and chemically, for successful reverberatory smelting.
Lime in the roaster charge appears to assist the thoroughness of the roast, whilst an incipient slag formation is commenced owing to the juxtaposition of basic oxides and silica, in the hotter parts of the roaster furnace.
2. Rapidity of melting is an indispensable feature of modern work. ”

“ If, however, a little sugar or salt is added to the water it increases its density, and the heat rises to 224° before the steam escapes. The heat can be raised also by covering the pot and confining as much of the steam as possible. Where violently boiling water is recommended, as for rice and green peas, the object is not greater heat, but to keep the grains and peas separated by the turbulence of the water. ”

“ I then transferred the weighed sample to the crucible, the melted potash in which readily wetted the graphite rock. The mass was then gently heated, and occasionally stirred with a piece of silver wire. The heat never need be much above the melting point of the potash, though toward the last I have been in the habit of raising the temperature slightly, to insure the complete decomposition of the melt. ”

“ The hold, after being floored, scrubbed, and whitewashed, was converted into a room for the crew; the cook-stove was brought down from the galley and placed in the centre of it under the main hatch, in which hung our simple apparatus for melting water from the snow or ice. This was a funnel-shaped double cylinder of galvanized iron connecting with the stove-pipe, and was called the "snow melter." A constant stream poured from it into a large cask, and we had always a supply of the purest water, fully ample for every purpose. ”

“ This range, to be kept up to the mark of duty, when fed by the light dry fir wood used here, must be crammed unceasingly; it gulps down a half-dozen sticks in as many minutes and immediately sulks for more. To keep the pot boiling with such fuel requires eternal vigilance. ”

“ The iron is melted in about an hour and a half, and no flux or addition of any kind is made use of. A pot will last for fourteen or even eighteen successive meltings, provided it is not allowed to cool in the intervals; but if it cool, it will probably crack. These pots it is said can bear a greater heat than others without softening, and will, consequently, deliver the metal in a more fluid state than the best Birmingham pots will. See a figure of the crucible mould under Steel.
CRYSTAL, is the geometrical form possessed by a vast number of mineral and saline substances ”

“ Anaconda, indicating Foundations, Hearth, and Bracing.
(a) Because the hearth must be kept as hot as possible, so as to ensure rapid melting of the charge and maintain the products in a perfectly fluid condition. Any circumstance tending to cool the hearth is rigorously avoided, this being the contrary of the older practice. The protective influence of the heated matte-pool in modern work preserves the bed from the corroding effects of fresh oxidised charges, and in consequence, the maximum degree of heat can with safety be maintained on the furnace hearth. ”

“ Regulation of Furnace by Draft Pressure.—It has already been pointed out that rapid combustion of fuel, and consequently rapid melting, is greatly assisted by good draft through the furnace. In modern practice, where the factors, such as charge composition, nature of fuel, and furnace proportions, have been satisfactorily arranged for independently, the actual working of the furnace is regulated by the draft pressures. ”

“ If it is chilled too slowly a strong “hoggy” flavor is developed, which it is impossible to eradicate from the fresh product. The leaf lard should be chilled for twenty-four hours in a temperature of 32° to 34° F.
Melting. —It is put through a hasher of the Enterprise type to an open top water jacketed kettle, similar in type to an oleo [342] kettle. Frequently the melting kettle is a wooden vat with a galvanized iron kettle inside, the space between the wooden vat and the galvanized kettle being filled with water which is heated to the desired temperature for melting the product. ”

“ Smelting is often confounded with melting, as the names are somewhat alike, but the processes are entirely different; in melting, the metal is simply liquified, in smelting the metal has to be produced from ores which often have no appearance of containing any, as in the case of iron-stone, which looks like brown clay. By way of experiment let the reader take a small portion of “litharge,” which is a reddish powder, mix it with a drop of oil into a thick paste and place it on the end of a flat piece of charcoal or wood, and direct the flame of a candle upon it by means of a blow-pipe ”

“ In pot furnaces, on the other hand, the composition of the glass can be more accurately regulated, and the molten glass itself can be more effectively protected from contamination either by matter dropping into it or by the action of the furnace gases, while in pots it is also possible to effectually melt together materials which, in the open basin of a tank, could not be kept together long enough to combine. ”

“ The supply of heat required for the smelting of the charge and the thorough fusion of the products depends entirely on the intense combustion of the iron and sulphur constituents, and the greater the proportion of these materials oxidised per minute, the higher is the temperature. As has been already noted, such heat intensity increases at a rate greater than the mere arithmetical increase in the fuel proportion, by reason of well-known thermo-chemical laws regarding mass effects. ”

“ We thus arrive at the interesting conclusion, that [Pg 30] the heat which we get from coal is sunlight in another form. For every pound of coal that we now burn, and for every unit of heat or work that we get from it, an equivalent quantity of sunlight was converted into the latent energy of chemical separation during the time that the coal plant grew. This energy has remained stored up in the earth ever since, and reappears in the form of heat when we cause the coal to undergo combustion. ”

“ We may now understand what happens when something humid—say a sole—is put into a frying-pan which contains fat heated above 212°. Water, when suddenly heated above its boiling-point, is a powerful explosive, and may be very dangerous, simply because it expands to 1,728 times its original bulk when converted into steam. Steam-engine boilers and the boilers of kitchen stoves sometimes explode by becoming red-hot while dry, and then receiving a little water which suddenly expands to steam. ”