BOILER. This name is now most com monly applied to the close vessels used for the generation of steam. Such boilers, to les sen the danger of explosion, are almost inva riably made of wrought metal, which, if burst, will tear rather than fly to pieces, as cast me tal would do ; and the plates made for the purpose are formed of the best and toughest metal, and rolled or wrought with peculiar care. Engineers differ as to the comparative merits of iron and copper as a material for steam-engine boilers. Most however admit that iron, when of good quality, has the great est cohesive strength, although the greater uniformity of texture in sheet-copper renders it safe to construct copper boilers of less thickness than those of iron, to withstand a given pressure. Further than this, supposing an explosion to occur with a copper boiler, it is likely only to produce a rent or tear in the metal, while an iron boiler, even though wholly of wrought plates, is frequently blown to pieces.
Dr. Ritterbandt's plan of removing from steam-engine boilers the incrustations with which they become coated, is a valuable re cent improirement. All the fresh water em ployed in boilers contains lime, in the form of a soluble bicarbonate. The heat converts this into an insoluble carbonate, which falls to the bottom of the boiler, and carries with it any floating masses of other insoluble matter. When salt water is used the same results oc cur, but in addition to this, the carbonate forms nuclei for the accrescence of sulphate of magnesia, chloride of sodium, and other saline compounds, which crystallize and precipitate much sooner than would otherwise be the case. The incrustations so formed within the boiler thicken its substance, occasion a greater ex penditure of fuel for the heat to reach the water, and renders the boiler liable to burst ; because as the incrustation is not so good a conductor of heat as the metal, the latter be comes burnt and weakened before the heat of the furnace can penetrate through the incrus tation to the water, and thus explosion may occur. Dr. Ritterbandt's method is a chemical
one. He introduces into the water of the boiler some ammoniacal salt, the acid of which, mixing with the lime, will form a soluble salt instead of an insoluble carbonate of lime. It is not therefore simply a cure for a disease ; it is a prevention of the disease from taking place at all, and is on that account a very scientific method. There are many ammoni acal salts to choose from, such as the muriate, the acetate, and the nitrate. The quantity of ammoniacal salt used must depend on the quantity of lime in the water.
The Times gave valuable testimony, in 1847, to the efficacy of Ritterbandt's process in the following paragraph ;—" The invention has been tried for nearly twelve months upon the boilers of the engines printing the Times, working on an average seventeen hours per diem throughout the year. Not only have the boilers been kept perfectly free from deposit, but an incrustation which was formed pre viously to the application of the invention has been completely removed. We can fur ther state, that neither the boilers nor any part of the machinery, has been in any, even the slightest degree acted upon or injured by the action of the remedy in question." The patented improvements in steam-en gine boilers, introduced within the last few years, are so varied that we cannot even enu merate them.