14

DYEING AND CALICO PRINTING.

Boiler Incrustations.

As water is used for the produdtion of steam a word may be said here con-cerning boiler incrustations. These are chiefly due to the salts of lime(carbonate and sulphate) contained in water becoming deposited from it byevaporation and forming a hard stony crust inside the boilers. As the com-position and quantity of mineral substances held in solution in water varyaccording to the water itself, it is obvious that no general specific againstboiler incrustations can-be given. The number of substances proposed forthis purpose is too large to be enumerated ; suffice it say that the adlion ofsome is simply mechanical, interposing such salts between the particles of thelime salts as will prevent their forming a solid crust, while others adt chemicallyby bringing about double decomposition, and, lastly, several organic substances,such as sawdust, spent tan, potatoes, molasses, catechu, and others appear toadt partly mechanically, partly chemically, although it is not possible tospecify precisely how and why.

Rain water, which itself is too pure to give rise to these incrustations, cannotbe used alone for boiler purposes, for it has been found to exert a highlycorrosive adlion upon the iron plates and fittings. It can, however, beadvantageously employed in conjundtion with hard spring and river waters,and has the effedt of diminishing the incrustation merely as the result ofdilution. The drain pipes leading from the roof of the fadtory may be placedin connedtion with the tank or well from which the supply of water is drawnfor the boilers. It will be seen hereafter that the same remedy is efficientboth as a means of preventing incrustation and obviating corrosion, and thatby using one of the alkaline substances about to be specified this twofoldadvantage may be secured. Iron will not rust when immersed in water con-taining a mere trace of caustic alkali, and it is a common observation thatthe iron vessels used in the preparation of potash and soda remain for anylength of time free from all appearances of rust. This singular property is nodoubt susceptible of important applications; amongst them may be mentionedthe better protedtion of iron ships from the attack of bilge water, of hydraulicrams, smiths’ tools, and other objedts liable to be placed at times under theinfluence of water. Some forms of “ surface condensers ” become quicklycorroded in consequence of the purity of the water accumulating in them bythe process of distillation, and a small dose of caustic alkali is then useful asa means of protedtion ; the engine cylinders are also to some extent preservedwhen alkaline anti-incrustation fluids are introduced into the boiler, for theminute quantity which is carried forward mechanically in the form of spraymixed with the steam suffices to preserve the iron ; but a tendency topriming undoubtedly results from a too liberal use of soda or other alkaliin the boiler. It will in pradtice be found easy to adjust the proportion ofthis ingredient so as to secure immunity from corrosion and incrustation, andat the same time avoid the tumultuous kind of ebullition known as “ priming.”In all cases it is advisable to carry out a rigid system of inspedtion, and it isonly in the way of saving fuel and labour that the application of boiler-fluidsis to be recommended.

Much benefit has often resulted from a coating of coal tar, or “ dead oil,”applied to the interior surfaces below the water line when the boiler is open