A.—­It will of course be impossible to recapitulate all the purposes to which engines are applicable, or to specify for every case the amount of power necessary for the accomplishment of a given amount of work; but some examples may be given which will be applicable to the bulk of the cases occurring in practice.

693. Q.—­Beginning, then, with the power necessary for threshing,—­a 4 horse power engine, with cylinder 6 inches diameter, pressure of steam 45 lbs., per square inch, and making 140 revolutions per minute, will thresh out 40 quarters of wheat in 10 hours with a consumption of 3 cwt. of coals.

A.—­Although this may be done, it is probably too much to say that it can be done on an average, and about three fourths of a quarter of wheat per horse power would probably be a nearer average.  The amount of power consumed varies with the yield.

Messrs. Barrett, Exall, and Andrewes give the following table as illustrative of the work done, and the fuel consumed by their portable engines; but this must be regarded as a maximum performance:—­

Number of | Weight of | Quarters of | Quantity of | Quantity of Horse Power.| Engine. | Corn thrashed| Coals consumed| Water required
| | in 10 Hours. | in 10 Hours. | for 10 Hours
| | | | in Gallons.
------------|-----------|--------------|---------------|----
-----------
|Tons.  Cwts.| | Cwts. |
4 | 2 0 | 40 | 3 | 360
5 | 2 5 | 50 | 4 | 380
6 | 2 10 | 60 | 5 | 460
7 | 2 15 | 70 | 6 | 540
8 | 3 0 | 80 | 7 | 620
10 | 3 10 | 100 | 9 | 780
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694. Q.—­In speaking of horses power, I suppose you mean indicator horse power?

A.—­Yes; or rather the dynamometer horse power, which is the same, barring the friction of the engine.  At the shows of the Royal Agricultural Society, the power actually exerted by the different engines is ascertained by the application of a friction wheel or dynamometer.

695. Q.—­Can you give any other examples of the power necessary for grinding corn?

A.—­An engine exerting 23-1/3 horses power by the indicator works two pairs of flour stones of 4 feet 8 inches diameter, two pairs of stones grinding oatmeal of 4 feet 8 inches diameter, one dressing machine, one pair of fanners, one dust screen, and one sifting machine.  One of the flour stones makes 85, and the other 90 revolutions in the minute.  One of the oatmeal stones makes 120, and the other 140 revolutions in the minute.  To take another case:—­An engine exerting 26-1/2 indicator horses power works