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clean lime, are easily removed and will brush off as a dust, forming a striking contrast to the difficulty encountered in removing the grease and dirt from the shell and tubes of a boiler which has not been treated with a lime-saturated feed. A lime-feed is especially necessary. The feed must be constant, regular and in very small quantities. Lime put in the boiler before closing up has in no way the same effect, and only slightly prevents the deposit of oil and grease and the generation of dangerous acids; it also to a much greater extent chokes and dis- colors the gage glasses. ' Lime before closing up is only useful as a preservative to the shell of the boiler, by rendering the water alkaline. With regard to the use of lime in the feed, the important question arises as to what quan- tities should be used. There are several ways of measuring the quantities required: (1) By H. P. developed. (2) By the number of tons of feed water used per 24 hours. (3) By the alkalinity test. (4) By the number of square feet of internal boiler surface. (5) By the number of tons of water in the boiler at working height and when full. The alkalinity test is, of course, but a check on the others, and is only useful as a means of knowing when to commence and when to leave off using lime. The number of tons of water in the boiler is the only guide for the quantities of lime to be used when preparing a boiler for steaming, or when pumping up to full from empty. For this the general rule is 3 Ibs. of lime per ton of distilled water, if the boiler is going to stand, and 1% lbs. if it will shortly be steaming. The number of square feet of internal boiler surface is of little use as a guide, except for a standing boiler, and the quantities given above for saturation apply also in this case. The number of tons of water evapor- ated per 24 hours is the surest means of gaging the necessary amount of lime feed, but the lime feed for auxiliary and main engine work must be different, as in all ships the auxiliary machinery is respon- sible for most of the oil in the feed water. As the water evaporated is directly pro- portional to the coal burnt, the number of tons of the latter is perhaps the read- lest guide. : When the boilers are working on the main engines, they are, as a rule, also on the auxiliary machinery, and the extra amount of oil supplied by the auxiliary machinery is so distributed over the in- creased number of boilers as to be prac- tically negligible. The increased efficiency of the steam when on the main engines, and consequently the less coal burnt per "TRAE Marine. REVIEW ton of water evaporated, must also be considered in this matter. So that in practice only two proportions of lime per ton of coal burnt may be considered: (1) For boilers on auxiliary work only. (2) For boilers on main and auxiliary work combined. Under modern conditions of marine engineering, the amount of oil in emulsion per ton of feed water is very small, and the amount of lime required is small in proportion--but to be effective must be fed in very regularly and in very small quantities. The following rules are based on the assumption that one ton of coal evapor- ates 10 tons of water. Boilers on auxiliary work only require about three ounces of lime per ton of coal burnt, to kill the oil in emulsion and neu- tralize as far as possible all free gases. Boilers working on main and auxiliary machinery combined require 1% to 2 oz. of lime per ton of coal burnt. These quantities assume that the boilers are already charged to at least 1% lbs. of lime per ton of contained water. In either case reduce the lime to one oz. per ton of coal, when the boiler gives a very sharp reaction to the litmus test. Scum:. about.:k.to-2 i, au. the, eage glass and blow outanother one inch when the boilers have received 1% to 2 lbs. of lime per ton of contained water through the feed. The scumming and blowing out should only be done when the boilers are working easily. If carefully applied these rules should keep the boilers in good condition. When W. T. boilers are being forced, the lime feed should be eased or alto- gether ceased, to prevent the boilers priming. Always give the boilers a good scum- ming and blowing out when finishing with the main engines, and fires are dying out. This is best done when-steam has fallen to between 50 and 20 lbs. pressure. A boiler which is shortly to be cleaned and is working easily may receive a spe- cial "finishing" or cleaning mixture, made of one part soda and two parts lime. Eight ounces of this mixture per water in the boiler is sufficient. It should be fed in gradually at the rate of not more than 1 lb. per hour. As a boiler in this condition will not stand any forcing, this mixture should be the last thing it receives before the fires are dying out, and it should be well scummed when pressure has fallen to 30-50: Ibs... Phe water should be run into the bilge as soon as possible after the boiler is cold, and the boiler thoroughly cleaned before again using. As regards small tube boilers special at- tention must be paid to the lime feed. Lime, in excess, may easily cause prim- At ing in small tube boilers, especially in some classes of them. This necessitates very careful adjustment of the lime mix- er. These boilers, when subject to forc- ing, should have not more than one ounce of lime, fed in regularly and well di- luted, per ton of coal. It should not be put into the mixer in too great bulk. The mixer should be changed at least once every eight hours, or every four hours if too much labor is not involved. A small (or in fact any) W. T. boiler may prime on lime being first introduced into the feed water. This, as a rule, only occurs when the lime is put into the feed in too great a quantity at a time. A boiler often primes on the slightest change of density in its feed. But after a short time it gets "used" to the slight in- increase, and the priming ceases. The feed may then be maintained at the in- creased density, without any further pro- test on the part of the boiler. The use of lime--especially in excess-- is liable to produce discoloration of the gage glasses, It will not be amiss here to give the method usually used to clean a discolored glass, also to hint that it may be practi- cally overcome by a regular and constant lime feed in small quantities. When discoloration has taken place "boiling out" the discolored glass with vinegar or a weak solution of some handy acid, such as muriatic (spirits of salt) will remedy this. The procedure is to close the steam and water cocks and then drain the glass and close the drain cock. The top plug is then removed, and the glass is cautiously three parts filled with vinegar or a weak acid solution. The plug should then be replaced and the water cock cautiously opened, followed shortly after by the steam cock. Allow the solution to boil for a few minutes, then drain and blow through in the ordin- ary manner. This should leave the glass clear. It is important that this should only be done by an experienced and care- ful person, as the work involves the risk of a severe scalding. Litmus is the recognized test for alkal- inity. A well-fed boiler should always give a sharp reaction to litmus, but when a sharp clear blue is immediately obtained, ease the lime feed'to one ounce per ton of coal, or even less, as additional lime will only cause the glasses to discolor. Experience with litmus will enable an engineer to judge exactly how his boilers are working, and so to regulate the lime feed as to assure the good condition of the boiler shell and tubes, and facilitate the cleaning of the boilers when opened out. A much more delicate test for alkali- nity is phenolphthaline and, where avail- able, it will be found very useful as an al- kalinity test for the feed water. |