TRANSACTIONS OF SECTION G. 



525 



The distribution of the units of heat have, in this case, heen carefully worked 

 out with the following results : — 



The water evaporated per lb. of coal in this test was 11*45 lbs., or 12*15 lbs. 

 from a temperature of 212°. 



As an example of the comparison which exists between the mode of settin°- 

 boilers just referred to, and the old setting of the cylindrical boilers with which 

 the first test referred to was made, it may be stated that with the mode of setting 

 adopted for the double tubular boiler no less than 90 per cent, of the total outside 

 area of the boiler is exposed to the gases from the Jires. In the case of the 

 cylindrical boiler, the gases impinged on only 32 per cent, of the total outside area, 

 such comparison being in the ratio of 3 : 1. 



The author ventures to enumerate below some of the chief improvements 

 which might be made in the construction, arranging, and working of plant of the 

 class described in this paper : — 



1. The fixing of boilers of an improved description with a minimum thickness 

 of plates and a maximum area of heating surface, the latter and the mode of 

 carrying the gases being so arranged as to absorb as much as possible of the heat 

 passing from the fire. 



2. Special attention should be paid to the manner in which air is admitted to 

 the fire and to the working of the damper. 



3. The air admitted at the firegrate should be so intermingled with the gases 

 from the fire as to enable a minimum quantity of air to be used, care bein°- taken 

 to prevent carbonic oxide passing off unconsumed. 



4. The application of such form of firegrates, and such mode of firing as will 

 enable the cheapest quality of fuel to be used. 



5. The complete covering of all exposed hot surfaces of the boiler, steam pipes, 

 &c. 



6. "Where water is scarce, the application of the best form of water-heater. 



7. "Where water is plentiful, the adoption of an approved form of condenser. 



8. Steam jacketing of the cylinder, and careful attention to mechanical ac- 

 curacy in the construction of the engine and of all the moving parts. 



9. The application of the principles of variable expansion when the work done 

 by the engine varies. At the Blackwell Colliery in Derbyshire, one of the wind- 

 ing engines is fitted up with Guinotte's automatic variable expansion gear, and expe- 

 riments made with and without the gear at work showed the consumption of fuel to 

 be in proportion of 77'5 : 100 in favour of the expansion gear. 



10. In the case of winding engines, the adoption of drums of varying diameters 

 so as to reduce the power which has to be expended during the first few strokes 

 in winding, the load upon the engine thus being equalised. 



11. As a general principle the use of steam at a high temperature in order to 

 have the greatest possible difference in temperature between the steam when it 

 reaches the cylinder, and when it has done its work. 



In the application of such improvements to ordinary steam engines the saving 



