It is advantageous to have two cupolas, and work them alternately, the common sizes being from 2 feet 6 inches to 4 feet, and the total height of the blast stacks varying according to the work and nature of the fuel. The positions of the tuyeres and charging holes are important. In the former case the position is determined by the class of work to be done. Where heavy castings are made, and consequently a large body of metal is required, the tuyeres are placed high, the object being to have a large body of metal in the bosh, to retain the heat, also giving a greater facility for the different brands of pig and scrap to thoroughly blend, melting more and running longer heats. Where small castings only are required, the tuyere is placed lower, and has the advantage of saving fuel, but the same depth of fuel is required over a low tuyere as over a high one. The position of the charging hole is most important, because the higher it is in reason, the less proportionately the consumption of fuel will be; for this reason high cupolas hold the heat, make the iron hotter, and melt it faster. This can be practically exemplified where convenient, by raising the charging hole for two or three charges. It is evident that the more charges there are in the cupola, the greater amount of heat will be absorbed which otherwise goes up the blast stack, and consequently when the charge comes to the melting stage it will melt quicker and hotter.

The fuel should be good hard coke, as free as possible from sulphur. Speaking generally of coke, the heating power may as a rule be taken to approach somewhat closely to the content of carbon. The purest samples of coke will only contain about .5 per cent, of sulphur, whilst the most impure will have about three times that amount present. It should be as free as possible from black ends, because these contain more of the volatile matter existing in coal, and they are more porous, absorbing a greater quantity of moisture when quenching, than dense coke. Good coke should not exceed 1.25 per cent. of volatile matter besides moisture, and the lower the content of volatile matter, including water, the less will bo the loss of heat. Ash has a detrimental effect, because it is fused, consequently more limestone is required, and it probably brings in the sulphur; however, a small increase in the content of ash may be to a certain extent ignored, providing that the mechanical properties of the coke are such that it will withstand a good crushing load, is hard, and almost of a metallic lustre. Soft, tender, friable coke must be avoided, because it cannot withstand the weight of the charges, and is more easily affected by C02, consequently is consumed faster and melts less metal.

To those who have charge of cupolas this result is well known; with the former they may probably finish charging several hours before the latter, and then not as great a quantity of metal melted. The analysis of coke may vary in carbon from 87.5 to 95.5 per cent.; sulphur .3 to 1. 5 per cent.; ash 2.5 to 10 per cent.; moisture 1.6 to 3.5 per cent.; and some cokes may he found dry; hut as with steel, the chemical properties should always be bracketted with the physical, otherwise it is useless. The quantity consumed is about 1.5 to 1.75 cwt. per ton of iron melted, or 2.5 to 2.75 cwts. per ton of castings passing over the weighing machine, which is about equivalent to American consumption; and the quantity of iron melted in a 4-foot cupola is about 3. 5 to 3.8 tons per hour, including lighting up, a fair day's work being from 35 to 40 tons per ten hours' shift But this of course varies according to the work in hand; as much as 70 tons may be got out in a twelve hours' shift with continuous working, there being a greater economy in fuel by having heavy charges. The foundry foreman should keep a strict account of iron melted, castings passing over the weighing machine, and the average consumption of coke, thereby always having a check upon the cupola account.

In preparing the cupola, it is first well cleaned out, especially for 6 or 8 inches above the tuyere holes, using hammer and chisel when necessary, cleaning the whole of the inside carefully without removing the glossy skin; all furrows should be filled up with ganister, and under good management the lining will wear very evenly. The bottom is then made with moist black sand, which is well rammed, and afterwards sleaked over with clay wash or blacking, it being slightly inclined to each tapping hole. The tapping holes are then well rammed up with ganister and red sand from the outside against an inside support, there being a round bar inserted to form the tapping hole, which is not more than 2 or 3 inches long. The fire is then lighted and the breast built up with hard burned coke, the plate put on and black sand rammed between, the tapping hole in this plate being made with ganister. After the blast has been turned on, it is allowed to blow through the tapping holes for twenty minutes or half an hour in order to get them thoroughly dry, which is important, otherwise much trouble may he caused, perhaps necessitating the use of a sledge bar. About the average time of starting the fire is two hours before the iron is charged, and the coke should he from 12 to 18 inches thick above the tuyeres, burning well and evenly throughout, but it is possible to tap out in an hour from lighting up. Each time after tapping, the hole is stopped with a mixture of clay and coal dust, the latter preventing the clay from setting too hard and causing it to crumble when tapping out. The stopping is applied on a rod, and is best inserted at a slight angle from the top of the metal, which lessens the risk of it being washed away and the consequent filling of shank ladle3 too full, running upon the floor, and general confusion.