STEAM BOILERS 137 



Quantity of Chemicals to Use. When treating water con- 

 taining carbonate of lime and sulphate of lime, caustic soda 

 may be used either by itself or in combination with carbonate 

 of soda, depending on the relative proportions of carbonate of 

 lime and sulphate of lime present in the water. The amount 

 of caustic soda or carbonate of soda to be used per gallon of 

 feedwater can be found as follows: 



Rule I. Multiply the number of grains of carbonate of 

 lime per gallon by 1.36. If this product is greater than the 

 number of grains of sulphate of lime per gallon, only caustic 

 soda is to be used. To find the quantity of caustic soda required 

 per gallon, multiply the number of grains of carbonate of lime 

 in a gallon by .8. 



Rule n. Multiply the number of grains of carbonate of lime 

 per gallon by 1.36. If this product is less than the number of 

 grains of sulphate of lime per gallon, take the difference and 

 multiply it by .78 to obtain the number of grains of carbonate of 

 soda required per gallon. To find the amount of caustic soda 

 required per gallon, multiply the number of grains of carbonate of 

 lime in a gallon by .8. 



EXAMPLE. A quantitative analysis of a certain feedwater 

 shows it to contain 23 gr. of sulphate of lime and 14 gr. of car- 

 bonate of lime per gallon. How much caustic soda and carbon- 

 ate of soda should be used per gallon to precipitate the scale- 

 forming substances? 



SOLUTION. By rule I, 14X1.36 = 19 gr. As this product 

 is less than the number of grains of sulphate of lime per 

 gallon, rule II is to be used. Applying rule II, (23 19) X. 78 

 = 3.12 gr. of carbonate of soda, and 14 X .8 = 11.2 gr. of caustic 

 soda. 



Use of Carbonate of Soda. Water containing sulphate of 

 lime, but no carbonate of lime, may be treated with carbonate 

 of soda. The amount of the latter that is required per gallon 

 to precipitate the sulphate of lime is found by multiplying the 

 number of grains per gallon by .78. When using soda, it is 

 well to keep in mind that it will not remove deposited lime from 

 the inside of a boiler. All that the soda can do is to facilitate 

 the separating of the lime, that is, cause it to deposit in a soft 

 state. This sediment must be removed periodically 



