material for the sand is either clay water or about 1 volume of powdered rosin to 30 or 35 volumes of sand, or 1 volume of unbolted rye meal to 12 or 15 volumes of sand. Sometimes, for coarse sand, a mixture of rosin and rye meal is employed. It has also been proposed to use potato starch, which has been previously heated to the temperature at which it is transformed into dextrin..

FITTING OF THE CORE IN ITS PLACE.

The rapping to which the pattern is subjected increases the size of the core prints; therefore, in order to insure a perfect fitting of the core in its place, either the core box should be slightly larger than the core print, or the latter should be slightly smaller than the core box, something like to of an inch, according to the dimensions and shape of the pattern. It is important that there should be no shake of the core when in the flasks.

MALLEABLE IRON CASTINGS

The manufacture of the so-called malleable iron castings, requires a metal in which all the carbon is in the combined state; that is to say, a white metal which parts easily and equally with its carbon in the subsequent annealing operation. A gray casting would be very slow in losing its carbon, and the metal would be honey-combed at those places where the uncombined or graphitic carbon was present. The metal preferred for such castings is a mottled pig, which is run with an admixture of scraps from the cupola. When a still better metal is desired, the pig iron is melted in pots, or in a reverberating furnace, and it is poured out when it has lost a certain amount

of its carbon. The proper time is ascertained by taking samples of the molten metal now and then, and casting them into small cylinders about five inches long and one inch in diameter. Two such cylinders are cast at the same time, one is allowed to cool slowly in the sand, and the other, while red hot, is cooled in water. The metal is ready for casting when the fracture of the cylinders is slightly mottled for the one cooled in sand, and nearly white for the other chilled in water.

The shrinkage of such white metal castings is greater than that of the same articles made of gray iron. A rough average is inch per foot.

CUPOLAS.

We see no change in the general description and principles of cupolas as described in previous editions of this book, although numerous inventors have brought forward modifications in the shape and dimensions of the furnace. Some give it an elliptical or conical section; others increase the number of the tuy eres or surround the cupola with a casing in which the blast may be heated, etc. It has been found in cupolas, the same as in blast furnaces, that in order to be effective, the hot blast must be very hot Then there is a real economy of fuel. But the estab lishment of hot air stoves does not pay for cupolas because the work of the latter is intermittent.

BLAST.

A steam blast, similar to that employed on locomo tives, has been applied to cupolas. That is to say, a jet of steam is made to escape at the top of the furnace, and the vacuum produced causes the atmos

pheric air to enter the cupola through the tuyeres. In this process, the amount of steam used is about equal to that needed for the motor of the fan. The saving is in the fan and the machinery to move it. The pressure of the blast is weak.

A better understanding of the principles of combustion, and of the best place for the greatest temperature in the furnace, has led of late years to the introduction of blast at a greater pressure than it is possible to obtain with the ordinary centrifugal fans. These latter, no matter how fast they are revolved, cannot give more than a certain amount of pressure. Other blowers, on the contrary, have their vanes so tightly constructed, that the air imprisoned within cannot go backwards, and is forced in front to the tuyeres.

Among the first blowers built on this principle, are those manufactured by Mr. Root. More recently, the Baker blower has been introduced into many foundries, and gives satisfaction. The Baker blower, being entirely of metal, it has been possible to make the lines of junction of the vanes with great accuracy, and thus to insure against leakage of the air or loss of pressure. The vanes of the Root blower are of wood, and wear out, or warp to a small extent; but Mr. Root remedies this by covering them with a kind of stiff ointment which it is easy to put on when needed. We have seen a ten horse power Baker blower working at a regular pressure of one to one and one-quarter pounds per square inch, which could be increased to three pounds by contracting the outlet. A column of one inch of mercury corresponds very nearly to half a pound of pressure per square inch,

FONDERIE A CALEBASSE

Is the Beigian name of small cast iron foundries producing principally small articles of hardware, ornaments, and such objects as those in which the strength of the metal is of secondary importance. They may manufacture a good metal by employing a good metal, but they generally use all kinds of scraps. This is one of the advantages of the calebasse process; moreover, the cheapness of the apparatus brings it within the reach of those with little means. There is no necessity to wait until enough moulds are ready for filling with the metal of a large cupola; consequently, there is an economy of foundry floor, of flasks, and of other foundry appliances. On the other hand, the consumption of fuel is comparatively greater than in a cupola; but the fuel may be of inferior quality, such as light coke, and even bituminous coal. The metal obtained is very hot and fluid, and it is possible to make the mixtures just such as are desired.

The furnace is like a foundry ladle, with trunions to move and turn it about; the shape is a truncated cone, the larger diameter of which is on top. Over this ladle or crucible is a movable cylinder of strong sheet iron, and at the place of junction there are two corresponding half circles which form the hole through which the tuyere passes The whole is placed against a wall and under a metallic hood.

The blowing apparatus is a fan, making from eight hundred to one thousand revolutions per minute, and connected with the tuyere by a leather sleeve, which allows of the ready removal of the tuyere, or of its inclination to various angles.

Both the crucible and the cylinder above are loamlined like foundry ladles. The crucible rests upon rammed sand, and when the cylinder has been clayluted on, it is surrounded by a bank of dry sand.

The start is with fuel alone and a light blast, and the charging begins when the ignition is thorough. As the operation proceeds, the blast, which was at first horizontal, is made to be more dipping. When the melting is finished, the sand is removed, and then the top cylinder; and the crucible is ready to pour its contents into the moulds, or into smaller ladles.

In about one and a half hours, from five to six hundred pounds of metal may be melted, and it is possible to make four such operations in a day.

SCAFFOLDING.

When scaffolding occurs in cupolas, it has been found advantageous to blow finely pulverized fuel with the blast through the tuyeres. The intense heat thus produced near the tuyeres is sufficient to melt the obstruction.

ORDNANCE.

In the preceding pages of this work, no mention is made of the casting of ordnance and projectiles. This omission is due perhaps to the objection Mr. Overman had to raising statues to military heroes, which objection extends, of course, to the implements of war. Perhaps, also, the author thought that it was unnecessary to repeat on this subject the already explained methods of loam, green and dry sand mouldings, which apply equally well to the manufacture of ordnance and projectiles.