It is almost impossible to work a cupola to a time-sheet, as one day it may be wanted to work fast, or perhaps two may be on together; another day cold or hot, hard or soft, according to the quality of castings required, that is generally speaking of contract shops; but with railway work, which is so regular and well known, it is very much easier to regulate and approach somewhat time-sheet working. Foundries noted for turning out castings of the required grade, run their heats separately, which can be done without dropping the bottom of the cupola, by clearing out through the breast the clinkers, etc, until it is certain that the cupola is clean. This of course takes from half an hour to one hour extra, and more coke is consumed. It appears almost impossible to run two heats of different grades of iron without getting them intermixed. This is especially the case where the charges are small, as there must always be globules of metal remaining about the fuel and sides; however, as a rule, one class of metal is run off before the other is seen to he coming down; especially in the cane of cylinders, when the bottom is run quite dry before the cylinder metal is seen to be melting. It is a good practice to put a charge of general iron in between a hard and soft grade. The iron never gets into the tuyeres or blast chamber, as by knowledge of the cupola and a careful watch this is prevented. The slag is also watched through the tuyere holes, and when it is seen to have risen high it is tapped out, perhaps about three times a day. Of course it can be higher than the tuyeres without entering, as the pressure of the blast carries it to the centre of the cupola. The blast chokes and chills the fuel at its entrance, and as soon as this is noted to be of any extent, it is rabbled into the centre of the cupola. Limestone is used as a flux. About 100 to 150 lbs. is sufficient for 4 or 5 tons of metal, a portion being put on with each charge. It also helps to clean the cupola and make it drop better, which is done after the last metal has been tapped out, the cinder and dirt being raked away. The drop is not absolutely the best form of cupola, although very convenient, and is only tolerated in foundries where it is not absolutely necessary to have the first and second heat hot. The bottom, having to be made every morning, is cold and damp, whereas with a permanent bottom it is always dry. In the latter case, the cinder and dirt have to be raked through the breast, and consequently requires a more room. It is very rarely that there is any metal left in the bottom, if so, never more than half a hundred-weight, which is picked out of the cinder and is good scrap.

Iron mixings generally consist of one of soft pig and two of good scrap, or two of soft pig and three of good scrap, but if a very soft casting is required, select two brands of pig and no scrap, because every time iron is melted it becomes harder; but it is not always advisible to use all pig, as a certain percentage of good scrap will make the castings stronger and cleaner. One-fifth of good scrap is used in casting the cylinders, the brands of pig being selected from experience: say Madeley Wood, Carron and best cylinder scrap. Wrought scrap and white iron generally give trouble, through not being intimately mixed, unless the charge is large and sufficient time is given for them to blend in the boshes, which will hold at least twice as much before twelve o'clock as after.

The moulding and casting of the double cylinders is about the moat important and difficult piece of work in the whole foundry. The casting must be perfectly sound and the metal of high quality, hard and tough, but at the same time capable of easy machining. The metal is poured into the mould as hot as it is practicable, because the hotter it is poured, the sounder and cleaner the cylinders will finish. Smooth-skinned cylinders may be obtained by dull casting, but soundness is sacrificed for smoothness. Hot pouring is a great trial to the mould, because the metal will find its way into poor joints and vents, the latter causing the easting to blow and scab, also destroying cores or mould if burnt in drying. There is not much risk as a rule in the mould; but the danger lies chiefly in the cores, as they are numerous and of complicated shapes. Great attention is bestowed in securing the vents and setting the cores in their prints, the moulder clearly satisfying himself that the loam does not plug up vents, and as little is used as possible, especially if the mould is going to be cast immediately. The hay rope round the body cores is bound as tight as the rope will stand, or it will slacken, and then it will be impossible to sweep up the cores solid and true. In making the cores a finer sand is used for the face than is required for the centre, where cinders are often used. Fine sand gives a smooth surface, but is bad for getting the gases away. They are put into the drying stove as soon as possible after making, because air-dried cores crumble. The cores are either made in boxes, struck up from a board, or as the S cores, partly made in a box and partly swept up, which is very handy for the moulder and easy for the patternmaker. The shape of the core-boxes can be clearly surmised by reference to the cores in the drawings of the cylinders, Figs. 57-60. The patterns are shown in plan and elevation in Figs. 53-56, all core prints being indicated by diagonal shading.