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is the point where permanent hardness scale begins to form. This scale is very hard and of a brittle nature. One of the purposes of treating boiler water is to change the chemical nature of this salt so that it will form mud instead of scale. Sodium salts are so constituted by nature that they are extremely sol- uble, never forming mud and never forming scale unless the concentration becomes extremely high, causing a saturated solution; in which case they will crystalize out. It is doubt- ful if this ever happens on the Great Lakes because of the great amount of mud which would accumulate in ob- taining such a concentration and of the limitation of the boiler itself. Practically the only objection to sodium salts in the water is their ef- fect upon the concentration, conse- quently upon the chemical balance in the boiler. This will be taken up un- der the discussion of concentration later on in this article. There is no way to eliminate sodium salts from the boiler except by the use of evaporators. The quantity of the salts can be reduced by blow-down but never eliminated and it is for this rea- son that they play such an important role in the control of boiler water concentration and chemical balance. Certain types of these salts may also have corrosive effects if not neutral- ized. Definition of Terms To avoid confusion we will define the more uncommon terms used. Insoluble and suspended matter, which in reality are the same thing, can properly be considered as noth- ing more nor less than mud. Soluble matter or soluble salts are the salts which are actually dissolved in the water. To give an example of the nature of soluble salts, dissolve in a glass of water a little table salt, sodium chloride, one of the soluble salts in the boiler. This salt can be removed from the water only by com- plete evaporation of the water and in order to reduce the amount of salt in a given volume of water, the water would have to be diluted. The concentration of a boiler water, as the term is most generally used, is the amount of salts present in a gallon of the water. This is expressed in grains per gallon. There as 7000 grains in one pound by weight. This gives us the weight of salts per gal- lon of water in the boiler. There are two kinds of concentra- tions; soluble and insoluble, the most important being soluble. The insoluble concentration is the concentration of mud suspended matter in the boiler. The soluble concentration is the con- centration of the soluble salts in the boiler. The chemical balance of a_ boiler water is the ratio maintained between the various chemicals in the water 18 and the ratio of their concentration to each other. Coagulation is the accumulation of many small particles of insoluable mat- ter into one large particle or floc and the increasing of the specific gravity of this large floc or particle so that it will settle out readily. Boiler Water Treatment Among the more important things to be considered in the treatment of a boiler water are: removal of old scale; prevention of scale formation; corro- sion and pitting; embrittlement of the boiler metal; foaming and priming; end the maintenance of clean, dry steam. The prevention of new scale requires the same type of treatment as the removal of old scale except in the case where old scale is the result of previ- ous improper treatment. A _ positive control of the removal of old and the prevention of new scale may be ob- tained if proper treatment is applied in accordance with daily tests of the boiler water, which in turn signify the chemical balance. Proper boiler water treatment applied so as to main- tain a correct chemical balance with- in the boiler will not only prevent for- mation of new scale and remove the old, but will also prevent corrosion and pitting, embrittlement of the boil- er metal and any tendency toward foaming. No single chemical will do this. It is necessary for proper tréat- ment, therefore, to use a number of different chemicals in correct propor- tions, each having its own work to do in the building of the chemical bal- ance. Careful consideration should be giv- en to the choosing of a treatment. Many compounds are based upon the coagulating properties of their consti- tuents. It is inadvisable to use a treatment which is primarily a co- agulant and which is made up in a Single general form because’ the coagulation of boiler water is a dis- tinct problem in itself and shouid not be confused with the treatment of the boiler water for the maintainance of chemical balance. The best results which can be hoped for from a boiler water treatment are outlined above and if these results are attained it is all that can be done with a boiler water treatment. Then comes the problem of the re- moval of the mud. Some treatments produce a great deal more mud or sus- pended matter than others. In these cases, of an undue amount of mud or suspended matter, the bad effect is sometimes demonstrated by blistered tubes or an excessive blow-down which is not only wasteful and harmful but costly as well. By the use of decon- centrators the mud which is formed in the boiler is continuously removed without a heavy blow-down loss. By removing the mud continuously a higher soluble concentration may be MARINE REVIEwW—July, 1934 carried without the danger of foam- ing and priming. Consideration will now be given to the causes of foam- ing and priming and the relation of concentration to the chemical balance. Foaming is due to improper surface tension of the water in the boiler with the result that the film of iiquid surrounding the steam bubble does not break and free the steam. This con- dition may be caused by too high a soluble concentration or by the mud being in a very finely divided state or that the chemicals in the boiler are unbalanced with relation to each other. It may also be caused by the saponification of oil in the boiler if sufficient quantities of oil get into the boiler. For the correction of foaming if it is caused by high soluble concentra- tion, the boilers should be blown down and the remaining solution of soluble salts diluted with fresh water. The soluble concentration, however, should never be so high as to cause this con- dition for it can be regulated easily by the use of a concentrometer, an in- strument to register soluble concentra- tion directly in grains per gallon. If, however, the cause of foaming is. such finely divided mud that it is prac- tically in a colloidal condition it may be corrected by the use of a coagulant. Too much coagulant, however, should not be used for it must be remembered that all coagulants form mud them- selves, some more than others. This condition can be determined by look- ing at a sample of the boiler water in a test tube and noting how long it takes for the mud to settle. Keep Oil Out of Boiler In connection with saponification of oil and grease, a mineral oil will not saponify; only grease or substances that have a fatty material in them will saponify. Some oils of this char- acter will cause trouble. Oil, how- ever, should never be allowed to get into the boiler. If, despite the most rigid precautions, oil should get into the boiler the only method of getting rid of it is to use a good coagulant to precipitate the oil. Then blow the boiler down to get rid of the precipita- tion of oil. It should be repeated that every means possible must be used to keep oil from getting into the boil- ers in the first place. Priming is usually the result of or- ganic matter present in the water and is the entire body of water’ in the boiler lunging back and forth. To avoid caustic embrittlement the correct sulphate alkalinity should be maintained as recommended by the American Society of Mechanical En- gineers. This in most cases on the lakes would be two grains of sulphates to one of alkalinity. If a boiler water treatment is ef- fective and gives the results expected from it, it should be fed either directly (Continued on Page 40)