In the year 1828, Mr. Anthony Scott, of the Southwark Pottery, Durham, took a patent for a very obvious and effective contrivance to abate this evil. His plan is to place a number of slabs or trays of metal stone or wood near to the bottom of the boiler, which it is said so reduces the agitation of the water during the ebullition, that nearly the whole of the sediment descends by its own gravity, and deposits itself in the trays, instead of on the bottom of the boiler. The transmission of the heat is not intercepted by this arrangement, while the trays are removable at pleasure, for clearing them of the sediment deposited upon them.
More recently, (in 1830,) Mr. William Taylor, of Wednesbury, took out a patent, having for one of its leading objects the prevention of the incrustation and removal of the sediment, without stopping the operation of the boiler. It consists of a sediment trough or vessel, extending the whole length of the boiler, immediately under it, with a valve opening at one end, through which a portion of water is occasionally permitted to escape with great velocity, arising from the pressure of the steam, that it may carry with it whatever deposit may have settled in the bottom. This arrangement is represented in the annexed sketch; a a is a cylindrical boiler, having a fire place b, and a flue within it ; c is the deposit vessel below the fire. When this in vention is applied to boilers which have the fire under, instead of inside them, the patentee applies a deposit trough on each side, and these must be shielded from the action of the fire.
The claim to invention under this patent is limited to the particular modifications de scribed; as deposit vessels have, before the date of Mr. Taylor's patent, been applied to boilers; and they are undoubtedly appendages of great utility. On account of the great deposition of salts, and other earthy matters, on the bottom and sides of boilers employed in steam boats at sea, it becomes expedient, in long voyages, to stop the progress of the vessel, in order to discharge the contents of the boilers, and fill them anew; for if the heat be continued after a considerable deposition has taken place, the steam can only be raised by a increased expenditure of fuel, and the augmentation of the heat materially injures the tenacity of the metal of which the boilers are composed. To obviate so great an inconvenience, Messrs. Mandalay and Field have proposed an arrangement of apparatus, by which the water is con tinually being changed, and for which they took out letters patent in 1824. These gentlemen state that from 20 to 30 per cent. of the quantity of water evaporated, being taken from the concentrated brine, will keep the water within a degree of saltness from which no practical evils will result, however long the boiling be continued; the quantity thus abstracted from the boiler being of course replaced by a like quantity of sea-water in its natural state. The abstrac tion of the brine is made by means of a small pump, with a loaded discharge valve, worked by the engine, and so proportioned as to draw from the lowest part of the boiler the quantity determined on, which may be regulated by a meter, sheaving the quantity of water driven off in the form of steam. The operation of the pump is, however, not to commence until the brine has attained a considerable degree of concentration ; it should for instance contain five times as much salt as common sea water does ; after this, every stroke may be made by means of the pump, to take as much salt out of the boiler as is deposited in the boiler by the separation of the steam used in that stroke. By
these means, the water in the boiler can never exceed a certain predetermined degree of saturation ; and whether the engine be working quickly or slowly, the quantity withdrawn may always be made to bear the same proportion to the quantity left in, thus avoiding one of the greatest evils to which steam vessels in making long voyages have been subjected. To economise the heat and con sequent expenditure of fuel, Messrs. Mandalay and Field further propose that the hot brine extracted by the pump be discharged into a vessel containing a series of metal pipes of small calibre, similar to a refrigeratory. Through these pipes, which lie immersed in hot brine, the supply water is to be made to pass in order to abstract the heat in its progress, and deliver the sea-water into the boiler in a heated state.
In the year 1824, Mr. Smith introduced, in some of the salt works of Lan cashire, a mode of evaporating brine, by the application of high-pressure steam under the salt pans; and as the surfaces of these vessels are very extensive, they are incapable of sustaining much pressure. Mr. Smith, therefore, tied the bottom of the boiler to the bottom of the Ran (which also formed the to of the boiler), by means of screw bolts and nuts, in the manner shewn at b in the sub joined sectional figure. Finding this arrangement productive of a safe and efficient generator of high pressure steam, he subsequently took out a patent for a modification of it, to be applied to steam engines. This modification chiefly consisted in the addition of the upper vessel a. The plan of these vessels is supposed to be a parallelogram, and the screw bolts about 9 inches apart in each uer, over their whole surfaces. The water is supplied by a force pump, as represented, and a number of gunge cocks are fixed at different elevations, as shewn in the drawing, to ascertain the height of the water, and the state of the steam in each vessel. e e are steam pipes; f is a safety valve to the lower chamber b, and g another to the upper chamber a. The patentee states, that "about two inches of water are put into the lower vessel, and the other being half filled, the fire is lighted, which quickly raises the water in the lower vessel to ebullition, the steam of which acts upon the lower surface of the upper boiler, giving out its heat to the water contained therein, and is thereby itself condensed; and being thus alternately vapourized and condensed, the upper vessel is con verted into a steam chamber of uniform temperature." Although this boiler is calculated to generate steam with rapidity, owing to the extensive surface of metal exposed to the direct action of the fire; and notwithstanding it must be deemed safer than most others of equal capacity and effect, by reason of the numerous tie bolts; it must, we think, be expensive in construction, and very difficult to preserve free from leakages.