J2 HHtLOSUFHICAL TRAK8ACTIONS. [aNNO 1735. 



hot water, and re-crystallized. No one before M. GeofFroy thought of extract- 

 ing this salt by crystallization, being always before sublimed. 



An Account of a Machine for changing the Air of the Room of sick People iti a 

 little Time, by either draiving out the foul Air, or forcing in fresh Air ; or 

 doing both successively, without opening Doors or Windows. By Dr. J. T. 

 Desaguliers, F. R. S. N''487, p. 41. 



Fig. ] , pi. 2, represents a case, secb, containing a wheel of 7 feet diameter, 

 and 1 foot thick ; being a cylindrical box, divided into 1 2 cavities, by partitions 

 directed from the circumference towards the centre, but wanting 9 inches of 

 reaching this, being open towards the centre, and also towards the circumfer- 

 ence, and only closed at the circumference by the case, in which the wheel 

 turns by means of a handle fixed to its axis a, turning in two iron forks, or 

 half concave cylinders, of bell-metal, such as a, fixed to the upright timber or 

 standard ae. 



From the middle of the case on the other side behind a, comes out a trunk 

 or square pipe, called the sucking-pipe ; which is continued quite to the upper 

 part of the sick person's room, whether it be near or far from the place where 

 the machine stands, or in an upper or lower story, or above or below the ma- 

 chine. There is a round hole in one of the circular planes of the machine, of 

 18 inches diameter round the axis, just where the pipe is inserted into the case, 

 by which the pipe communicates with all the cavities ; and as the wheel is 

 turned swiftly round, the air which comes from the sick room, is taken in at 

 the •centre of the wheel, and driven to the circumference, so as to go out with 

 great swiftness at the blowing-pipe b, fixed to it 



As the foul air is drawn away from the sick rooms, the air in the neighbour- 

 ing apartments gradually comes into the room through the smallest passages : 

 but there is a contrivance to apply the pipes which go to the sick room to the 

 blowing-pipe b, while the sucking-pipe receives its air only from the room where 

 the machine stands. By this means fresh air may be driven into the sick room, 

 after the foul has been drawn out. 



This machine would be of great use in all hospitals, and in prisons : it would 

 also serve very well to convey warm or cold air into any distant room ; or even 

 to perfume it on occasion. 



Fig. 2 represents the inside of the flat of the wheel, which is farthest from 

 the handle, and next to the sucking-pipe. 1,2,3, 4, represents the cavity or 

 hole which receives the air round the axis, having about it a circular plate of 

 iron, to hold all firm ; which plate is made fast to the wood and to the iron 



