Full text: A treatise on the cornish pumping engine (Appendix G)

24 
THE CORNISH PUMPING ENGINE. 
36. In order to fix the amount of coal savings produced by Watt’s engine, it was 
necessary to decide upon a standard of the performance of the old atmospheric 
engine, with which that of the new ones might be compared. For this purpose it 
was agreed between the parties that some experiments on a large scale should be 
tried as to the quantity of work done by a certain quantity of fuel in the atmospheric 
engine. These were undertaken by a committee appointed for the purpose in the 
summer of 1778, two engines at Poldice mine being selected for the trials. 
The following report of the committee will best explain the nature of their 
operations. 45 
“ Poldice Mines, October 30, 1778. 
“ We, the under subscribers, having carefully examined the books of the mine touching 
the consumption of coals of the two eastern engines during the months of August and 
September of this present year, and attended to the working of the engines during those 
months, do hereby certify, that the said two eastern engines did consume, in 61 days 
of those two months, 220 weys of coal, each wey being 64 Winchester coal bushels, which 
amount to 14,080 bushels in 61 days. 
“We do also certify, that the said two engines together do work pumps in four lifts which 
are 17 inches diameter in the working barrels, and the whole depth from whence these pumps 
drew water to the adit is 58 fathoms. 
“ We further certify, that the said engines did, during those months of August and 
September last, work the said pumps at the rate of 6 strokes of 5| feet long each in every 
minute, which amounts to 8640 strokes per 24 hours. 
“We have also made an accurate calculation, by which it appears that when the new fire 
engine to be erected by Messrs. Boulton and Watt is completed, and actually works a 
pump of the same depth of 58 fathoms and 17 inches in diameter, at the rate of 6 strokes of 
5| feet long each in a minute, and consequently making 8640 strokes per 24 hours, it will 
draw a quantity of water equal to that now drawn by both the present engines, 46 and conse 
quently, whatever smaller quantity of coals it uses than 14,080 bushels for 61 days when 
going at the rate of 6 strokes per minute, will be the real savings in fuel occasioned by the 
said new engine at that rate of going. 
(Signed) “ James Watt. 
“ Matthew Boulton. 
“ H. Hawkins Tremayne. 
“ Richard Williams. 
“John Williams. 
“ Thomas Brown.” 
At the time this report was written, it was not customary to estimate the per 
formance of the engines in the manner at present adopted, but it is easy to calculate 
the duty from the data above afforded: this has been done by Mr. Davies Gilbert in 
45 Copied from a Paper by Mr. Davies Gilbert. Phil. Trans. 1830, page 122. 
46 It is difficult to see what kind of “ accurate calculation ” was necessary to discover this fact.
	        
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