THECUB A REVIEW 31 



THE PREVENTION OF SCALE 



HANDY AND EFFECTIVE APPARATUS FOR PURIFYING FEED WATERS 



CAUSTIC POTASH FOR REMOVING SCALE 



For the treatment of moderate quantities of feed water in which carbonate of lime 

 predominates, handy and effective apparatus may be contrived by the engineer out of 

 one or more boiler tanks, in which the water is heated by exhaust steam through a 

 system of pipe coils, soda or other chemicals being used as reagents. By this means 

 very bad water may be purified of a large portion of its mineral matter, which is left 

 behind in the tank. Feed-water heaters, whether using exhaust or live steam, answer 

 the same purpose. In the lime process, 28 grains of caustic lime will give a total pre- 

 cipitate of 100 grains of carbonate, the 28 grains of caustic being themselves converted 

 into 50 grains of carbonate. 



But for various reasons, steam users often prefer to treat the water inside the boilers, 

 in which case the use of caustic lime forms a too bulky precipitate, and some other 

 reagent must therefore be employed. By using caustic soda, both carbonate and sulphate 

 of lime can be thrown down, and the process is more rapid than with caustic lime and 

 carbonate of soda. Suppose, for instance, a water contains 6 grains of carbonate and 

 8.16 grains of sulphate of lime ; by adding 3.75 grains of caustic soda to the water, 

 these at once become 6.3(3 grains of carbonate of soda, and 6 grains of carbonate of 

 lime are precipitated. The 6.36 grains of carbonate of soda decompose the 8.16 grains 

 of sulphate of lime, and are converted into 8.52 grains of sulphate of soda, and another 

 6 grains of carbonate of lime are precipitated. Altogether, 12 grains of lime are thrown 

 down, and the soda acts twice, first by absorbing an acid, and second by changing this 

 acid for another. When used in this way, 31 grains of caustic soda will precipitate 

 100 grains of carbonate of lime. Soda, therefore, will remove nearly double the quantity 

 removed by caustic lime from waters containing both carbonate and sulphate of lime, 

 but the cost of treatment by so'da is considerably more than by the lime treatment. The 

 following formulas will be found useful : 



1. Water in which carbonate of lime is present — For treating 1,000 gallons of water, 

 1,060 grains of carbonate of soda, made caustic with 560 grains of burnt lime, are 

 required for each grain of carbonate of lime per gallon. To produce the same result 

 with soda, IV2 ounces of caustic soda for each grain of carbonate of lime present per 

 gallon will be necessary for the treatment of 1,000 gallons. 



2. Waters containing sulphate of lime only — For each grain of sulphate of lime 

 per gallon, 1% ounces of pure carbonate of soda will be required to treat 1,000 gallons 

 of water. 



3. When both carbonate and sulphate of lime are present — As explained for carbonate 

 water (1), 1^L> ounces of caustic soda for each grain of carbonate of lime will pre- 

 cipitate the lime in 1,000 gallons, but this quantity will also throw down 1.36 grains of 

 sulphate of lime at the same time, so that if the proportion of sulphate does not exceed 

 the carbonate beyond the ratio of 8 to 6, the sulphate may be disregarded. If, however, 

 sulphate of lime is present in a greater ratio, carbonate of soda should also be added. 

 An excess of soda should be used to insure a proper reaction, which is greatly assisted 

 b}^ heating the water. 



Unless the soda used is of the best quality and free from adulteration, leakages at 

 the scams may be caused, or the plates and fittings may be attacked ; the use of impure 

 caustic soda has been the cause of much trouble in this direction. 



When, however, scale has formed on the internal surfaces and shell of the boiler, 

 there is an effective method (which the writer has practiced with success for many 

 years) of removing it. Caustic potash answers this purpose, especially when the scale 

 consists chiefly of mud, with sulphate and carbonate of lime and magnesia combined. 

 Caustic potash is the concentrated lye sold in grocery stores, but if it is required in 

 large quantities it should be purchased from wholesale druggists. Dissolve it in a 

 barrel of water, say 40 pounds to the barrel, and then pump it into the boiler ; this is 

 about 1/6 pound of potash per pound of water and is strong enough for the purpose. 



The method employed by the writer was as follows : One boiler was cut out of service 

 at noon on Saturday, the damper was nearly closed and the pressure let drop to 30 or 

 40 pounds. The potash being ready, the mixture was pumped from a suitable tank into 

 the boiler : continuing to pump clean water until the glass was full. The fire was then 

 allowed to die out, and the boiler left in this condition for at least 24 hours, when the 

 furnace was again lighted, and the steam pressure raised to 15 or 20 pounds. The fire 

 was then drawn and the boiler blown down ; the bottom doors were taken off, all the 

 chunks of scale which could not go through the blowoff cocks were removed, and the 



