SIS ECONOMICAL PROCESS FOR ETAPORATIOy. 



Apparatus de- This mill turns between two large circular planes, whicli 

 extend a little beyond the ends of the wings. These planes 

 form the top and bottom of a kind of drum, the circum- 

 ference of which is open, except two hoops, one at top, 

 the other at bottom, about 6 inches broad; and consequent- 

 ly leaving between them an opening of 371 inches by 7*86, 

 or 2916 square inches; for I suppose the distance between 

 the top and bottom of the drum to be 19| inches. 



The wings of the yentilator shouid boas broad as possible, 

 so that they can more without friction. 



ThQ top and bottom of the drum are connected of course 

 by pieces of wood at their circumference, which will di- 

 minish the opening. This may accordingly be estimated at 

 2400 square inches only: but this is of little importance 

 as it is sufficient if it be equal to the inhaling orifice, which 

 we shall estimate at 1000 square inches. . 



The bottom of the drum has a circular hole, GH, ,at 

 least 36 inches in diameter. The free surface of this should 

 be 1000 square inches. 



To this is fitted a cylindrical tube, I K, of the same diame- 

 ter, and descending perpendicularly about 40 inches. It 

 is supported so as not to rest on the lower part of the 

 apparatus. 



LM is a lid for the square box NOPQ. It is perfo- 

 rated with a hole corresponding to the tube I K, and from 

 this hole rises the end of a cylinder similar to that above^ 

 which fits exactly. Paper is to be pasted over t^jU j^i^r 

 that no air may escape. 



The box N O P Q is a rectangular prism, 8 feet 2 inches 

 square, by 5 feet 9 inches high, in which are placed twigs of 

 birch, without bark, and very clean, in regular beds, crossing 

 each other alternately, and leaving more open space at bot- 

 tom than at top. On this heap is dispersed the liquid to ba 

 evaporated, which enters by small holes in the lid, so as to 

 be distributed as equally as possible amongst the twigs. 



Between the twigs and the lid a space should be left free 

 in the middle at least a foot high, not to check the passage 

 of the air. The twigs also should not be too close, but 

 placed so that no horizontal section should contain less thaa 

 3000 square inches nearly. 



The 



