33 
the atmosphere, which in his experience never rise higher 
than from 5*5 to 6‘0 lbs. of steam for 1 lb. of coal, and from 
the increased results obtained apparently arising from increase 
of pressure as above referred to, he is disposed to suggest 
that the rate of evaporation of water per pound of coals in- 
creases with and bears some ratio to increase of pressure. 
With regard to the deposition of sulphate and carbonate of 
lime and mud on boilers, Mr. Graham stated that he had ex- 
perimented with more or less success with caustic soda, quick 
lime, muriatic acid, soap liquor, sawdust, spent madder, and 
logwood chips. Two facts in particular were noticed as 
regards the tendency of hard water to “scale,” 1st, That 
the sulphate of lime separates from the water where in 
contact with other substances, such as the bottom and sides 
of the boiler, or on solid matter floating in the water, such 
as sawdust, but that no precipitation takes place until the 
water has been concentrated by continued evaporation down 
to the state of a saturated solution, or to that point which 
may be termed the “salting point;” 2nd, That carbonate 
of lime and mud are principally liberated in the body of the 
water, and have but little disposition to adhere to the boiler, 
unless cemented by the sulphate of lime. 
Practically therefore it has been found that no scale of any 
consequence will be found on engine boilers with even such 
hard water and hard firing as Mr. Graham has been accus- 
tomed to, if one hundred gallons of the concentrated liquor 
in the boiler, equal to four per cent, of the feed water daily, 
and three hundred gallons or twelve per cent, on Saturdays, 
be run away through the usual mud machine, and if the 
boiler every sixth Saturday be run entirely empty and 
brushed out. The water used was so hard as to require from 
thirty-five to forty measures of Clark’s test liquor to soften 
it. There is little loss incurred by this mode of manipulating, 
as the chief discharge may take place at the close of each 
