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The quantity of lime required to sat- urate water varies with the temperature of the water--the quantity decreasing as the temperature increases. Three pounds of lime is required per ton of distilled water, when the temper- ature is 60° to 70° F., and one and a half pounds when the temperature has risen to 212° FE. A boiler which is to stand for any length of time requires at least three pounds of lime per ton of contained water --if distilled; more than this is not re- quired, as the surplus settles to the bottom "TAE. MaRINE. REVIEW water. These must be dealt with separ- ately and in another manner. (2) Lime as a preventative. Lime as a preventative neutralizes the oil and fatty. matter in the feed water and assists to render innoxious the oxygen and CO, held in suspension in the feed and make-up feed water. The dangerous oils and gases, which, when introduced into the boiler, do so much damage, are always found in the feed water in very minute particles; the oil, as a rule, in the ordinary feed water, coming from the condenser, the air and -- Q keam Lh xe ry ---- and may choke or injure the faces of the running-down valves. Half an ounce of caustic soda (NaHO) per ton of water is used by some marine engineers, as it is believed to assist the water to absorb the lime and prevent any salts of lime forming a hard deposit on the shell or tubes. It certainly assists in rendering the water alkaline and can do no harm, Boilers that are pumped up to working height and which will shortly be in action, do not require more than one and a half pounds of lime per ton of water and about a quarter of an ounce of caustic soda per ton of water if fancied. _ These quantities of lime.are simply pre- Servative, and are not intended to kill the acids and gases introduced by the feed --Cop-- gases in the make-up feed. Air is very often introduced by the ordinary feed having a fall from the air pump discharge before it reaches the feed tank level as shown in Fig. 1. Lime and oil have a mechanical affinity and mix easily even when large quantities of water are present; so that if sufficient lime in solution be introduced into each ton of feed water, as it flows on its way to the feed pump it is intimately mixed with the oil-laden water before reaching the boilers and combines with the oily particles. When the particles of lime and oil "mix" the alkaline properties of the lime so neutralize the acid-forming tend~- encies of the oil, that even when the com- bined particles of oil and lime which miss being caught in the filter find their way fe into the boiler, no dangerous acid is form- ed from the neutralized oil-laden particles. Practically the same process takes place with CO, and O when free in the feed or make-up feed water, only the more powerful chemical affinity, in this case, directs the movements of these particles. Lime, to be of use as an oil killer, must be fed in very regularly, very constantly, and in very small quantities to the feed water. An ideal feed is a constant stream of chemically pure lime water, discharging into the feed water and mixing with it on its way to the filter or feed pump. At present there are two mixers or tanks for this purpose. One is a tank ~ using hydraulic pressure as the mixing agent, and the other is a tank using steam for the same purpose. The first, which is illustrated in Fig. 1, consists of a large, built-up tank of three-sixteenths of an inch plate, and varies from three to six feet in length, and from two to four feet in diameter, and is so placed that its top is above the level of the feed-tank over- flow. -- A manhole is provided in the top plate and is used for cleaning and lime-charg- ing purposes. A pipe is led from the discharge side of the feed pumps into the top of this tank. In large installations a separate system of piping is led round the stokeholds, hay- ing a connection to each feed-pump dis- charge. The discharge water from this pipe is directed towards the bottom of the tank, where it stirs up the lime. On one side near the top a tap is placed discharging into a funnel. This funnel is attached -- to a pipe which leads the mixture of lime and water to the feed tank, where the lime and feed water are mixed before proceeding to the feed pumps. This is an extremely simple type of mixer, but, whereas it is a great improve- ment on the old method of putting the lime direct into the feed tank, it also has many disadvantages. (1) Power is lost, as the feed-pump pressure is utilized for mixing purposes, (2) the pressure of the feed-pump discharge rises as the boiler feed is checked, causing the mixing to be strongest when the feed required by the boiler is least, resulting in the greatest quantity of lime being given to the feed when the feed water is flowing most slowly and vice versa, the result being ir- regularity in the lime feed. Aes (3) The discharge water falling into a funnel is slightly aerated, thereby carry- ing air into the feed water. . (4). A long system of piping and sev- eral valves are required in a big ship or where several feed pumps are used. 3 (5) The bulkheads require to be pierc- ee ae (6) The tank is large for its work,