•B&6s6iticA.L PROciiss i»o* evaporation. ^ 377" 



it would require as much power to glye twice the velocity 

 to one fourth the quantity of air. 



This velocity, or that of 16 feel per second to 2450000 

 cubic feet of air, is well adapted to the present case, as it 

 does not require too great a power, and the dimensions of 

 the apparatus will not be inconvenient. We will suppose 

 A tnan to work at this rate for an hour, then to rest as long, 

 and after six hours of actual labour to have accomplished 

 his day's work. Having thus passed over the evaporating 

 matter ^450000 cubic feet of air, he will have produced an 

 evaporation of 4900000 grs, or rather more than 100 wine 

 gallons of water; and, as the pay of a day-labourer at 

 Paris is only 1 f. 50 cent. [I fid.], such a quantity might be 

 evaporated at this expense. To evaporate a similar quan- 

 tity by lire would take about two bushels of coals, which 

 at Paris would cost from 2s. 6d. to 3s. The labour of a horse 

 would be rather more expensive than that of a man, and 

 Would require a larger apparatus to be applied to the best 

 advantage: but where a larger machine is desirable, a 

 greater moving power is requisite. ■^^•' 



Having explained the principles of the process, we shall 

 J)roceed to describe the apparatus ; observing, that not 

 merely the dimensions, but the arrangeriient of several of / 



its parts may be considerably varied, without detriment to 

 the effect. 



t' Pl. X, %. 1, is a perpendicular section of the machine; Apparatus 

 ahd fig. 2 is a plan of it in the line A' B'. described, 



A B is 9, handle 15^ inches long, making a circuit bf 49 

 inches, which a man turns round in a second. 



B C is an axis, having at its extremity C a toothed wheel, 

 taking in a cogwheel D, which has twice as many Cogs as 

 the wheel has teeth, so that it makes but oiie firm Vhile 

 the wheel makes two. 



The cogwheel D is fixed on an axis D E, which rests hy 

 a pivot on the support E, and is kept vertical at F by a 

 brass collar, well fitted to it, but admitting it to turn with 

 ease. iiiitlnm x>i 



The axis D E carries six or eight wings 4 ^eet 10 inches 

 long. The ribs of these are of iron, and they are covered 

 with oilcloth, sor varnished cloth : for they should be both 

 i^trOng and light. 



This 



