BOILER No. 4. 



75 



which had been in service a number of years. The ratio of 

 water heating surface to grate surface, which is 33. 8 to 1, does 

 not show what would be called a deficiency of surface under 

 proper conditions, but in this case the surface does not appear 

 to have been of sufficient area to absorb the whole heat of the 

 products of combustion. The temperature of the gases was 

 482 degrees, and this high figure, taken in connection with the 

 fact of the boilers' age, is indicative of 

 the presence of scale on the interior 

 surfaces. The loss of heat thus pro- 

 duced is evidently the cause of the 

 somewhat low economic result. 



Boiler No. 4. 



Kind of boiler, . Horizontal return tubular. 

 Number used, . . Six. 

 Horse-power (colO 



lective, basis 12 xFour hundred and thirty. 



sq. ft.), J 



{Mixture of Anthracite 

 Screenings and Nova 

 Scotia Culm. 

 Age, Two years. 



Boiler No. 4 embraces a plant of 

 six horizontal tubular boilers, set in one 

 battery of brick work, as shown in the 

 following cuts. These boilers are ar- 

 ranged in such a manner that the 

 products of combustion, instead of 

 passing from the smoke arch at the 

 front into the flue, in the manner 

 usually followed, are carried back to the 

 rear of the boiler through the two upper 

 rows of tubes. The number of tubes 

 in each boiler is 77. Those in the lower 

 rows, which carry the products of 

 combustion forward, number 51, and 

 those in the upper rows, referred to, 

 number 26. The main flue is located 

 at the rear end and is made of wrought 

 iron. . This arrangement of tubes, and 



