THE DISPOSAL AND UTILIZATION OF RESIDUALS. 135 



long as the saturation point is not reached, but as this is 

 approached, there is a liability to deposit crystals. The 

 specific gravity of the contents of the washer is tested from 

 time to time, and when it reaches 50, a part is drawn 

 off, and clean water added in its place. In practice, 

 liquid is drawn at convenient intervals. The solution is 

 passed through two filter boxes containing sand, and the 

 clear liquid runs into a shallow evaporating tank. A very 

 small amount of heat, such as that furnished by the waste 

 from the exhauster engine, is sufficient to concentrate the 

 solution and secure the precipitation of the sulphate, which 

 is fixed and drained in the usual way. By the courtesy 

 of Mr. Harold W. Woodall, proprietor of the Wareham 

 gasworks, and Mr. Moon, I have had the opportunity of a 

 personal examination of the process, as in operation at 

 Wareham, and at the time of my visit an excellent clean, 

 white salt was being produced. 



Considerable confusion is caused by the use of several 

 methods of expressing the ammonia content of a gas- 

 works liquor. What one really wants to know is the yield 

 of sulphate per gallon. Each degree as indicated by the 

 Twaddel hydrometer is considered to be equivalent to 

 2 ozs. of pure oil of vitriol, i.e., to be capable of neutralizing 

 that quantity. This includes the fixed as well as the free 

 ammonia. Since 49 ozs. of pure oil of vitriol combine with 

 17 ozs. pure ammonia to form 66 ozs. of sulphate, it follows 



that i oz. will form =i'347 ozs. of sulphate, or that a 



49 



i liquor will form 1-347x2 = 2*694 ozs. To get at the 

 yield of sulphate from a liquor, multiply the strength pei 

 degree Twaddel by 2-694. This gives the yield per gallon, 

 and the content of the well being known, the total can be 

 calculated. 



