On Incrustations of Boilers using Sea- Water. 283 



made for the purpose of ascertaining when the sulphate of lime and 

 when the common salt deposited. He found, when he 



2 



evaporatedyTxths of the water, a trace of sulphate of lime deposited. 



4 

 „ jAths do. do. do. 



5 



„ TK^'ts, the sulphate of lime began to deposit in larger quantities. 



)) T7;ths, do. do. decided quantities. 



8 f sulphate of lime deposited in very large quantities ; 



10 ' t also magnesia and salt began to form. 



Mr. Eowan's experiment, although indefinite as to the quantities, 

 shows that the sulphate of lime begins to deposit before even one-half 

 of the water is evaporated. It is probable, therefore, that this quantity, 

 or more, would require to be discharged in order to prevent the forma- 

 tion of crust in boilers. 



A saturated solution of common salt, in distilled water, is given as 27 

 of salt to 100 of solution, and a saturated solution in sea-water is said 

 to be 36 of salt to 100 of solution. The former ratio has been chosen for 



27 1 



this comparison, so that ^j=^, or only— - th of the feed-water would re- 



quire to be discharged in order to prevent the formation of common 

 salt, and rxths to be neutralized by soda, to prevent the deposit of 



sulphate of lime, the Txth discharged being a saturated solution of 

 sulphate of lime and common salt. It is thus shown that by the 

 chemical method, it is necessary to discharge yTjth of the feed-water, 



and neutralize the sulphate of lime in rp-ths of it with soda, according to 



Mr. Napier's method, to prevent crustj and by the mechanical method, it 



5 



is necessary to discharge ?^ths. 



The quantity of soda ash (supposed to contain 50 per cent, soda) 



is found by the formula -T.^, of 777-. .Tin '^^ in of feed-water. 



For the purpose of illustrating the expense of both methods of 

 preventing crnst, and also the loss by the blowing-off method, the case 



