MECHANICS AND USEFUL ARTS. 55 



4. The boiler with two internal fire-places joined into one internal flue, 

 known in the neighborhood of Manchester as the "breeches boiler," 23 ft. 

 long and 8 ft. diameter, will, under similar circumstances, give 5'90 Ibs. of 

 steam; or, not including the heating of the feed-water, from 60 J F. 2l2' J F., 

 6'5S Ibs. of steam for each pound of coal burnt. 



5. That a supplementary boiler, under very favorable circumstances, gives 

 a saving of 15 per cent. 



6. That flues round a boiler, when cleaned out, and the sides of the boiler 

 scraped once a week, will give a saving of about 2 per cent. 



7. That a difference in the setting alone of the same boiler may produce a 

 difference in the result amounting to 21 per cent. 



8. That the difference between a good-shaped boiler, properly set, and a 

 bad-shaped boiler, improperly set, but both clean and in good order, may 

 amount to as much as 42 per cent. 



9. That a difference in firing only will produce a difference in the result 

 of 13 per cent. 



10. That the smallest loss by smoke burning, or by the admission of cold 

 air, either over the furnace door or in front of the bridge, or at the back of 

 the bridge, has been 1*7 per cent. 



11. That the loss arising from a scale of sulphate of lime, of not more 

 than one-sixteenth of an inch, amounted to 14*7 per cent. 



12. That neither wet coal, nor coal which had been out of the pit three 

 years, nor wet weather, nor a variation of temperature in the atmosphere 

 from 40 F. to 70 3 F., produced any appreciable difference of result. 



13. That windy weather gave a good result. 



14. That a comparatively thick and hot fire, with a good draft, uniformly 

 gave the best results. 



15. That the difference in the results obtained with different coals, all 

 from the immediate neighborhood, amounted to a loss of 11 per cent. 



16. That the same coals, reported to be from the same pits, will vary in 

 their results to the extent of 6 per cent. 



17. That when a boiler is worked solely for the purpose of heating by 

 means of its steam, dye-vessels, soap-cisterns, etc., if its available power, 

 with the steam at a pressure of 2 1-2 Ibs., be taken as equal to 100, then at 7 

 Ibs. pressure its available power will be 120, and at 10 Ibs. pressure it will be 

 130; the same quantity of coal being consumed in each case. This surpris- 

 ing result, at present unaccounted for, may be thus stated : That the same 

 weight of coal consumed in the same number of hours will work ten cisterns 

 at 2 1-2 Ibs. pressure, twelve cisterns at 7 Ibs. pressure, and thirteen cisterns 

 at 10 Ibs. pressure. 



18. That while we may reasonably look for improvements in the construc- 

 tion of the fire-place, in the form of boiler, in the addition of separate sup- 

 plementary heating surface, and in cleanliness, and may thereby effect a great 

 saving in the consumption of coal, we cannot, at the same time, expect much 

 saving from extension of flue space, when coated with soot, or for greater 

 length of boiler than four times the length of the fire-place. 



Mr. Graham stated in addition, that in consequence of the uniform low 

 results obtained by evaporation from boilers and flues open to the atmos- 

 phere, which, according to his experience, never rise higher than from 5'5 

 to 6'0 Ibs. of steam for each pound of coal burnt, also from the increased 

 results obtained with increase of pressure, and apparently due to that con- 



