of a Condenser and Air-pump, 141 



ring of mahogany. But if the joint require to be frequently se- 

 parated in using the instrument, it may be applied moistened 

 to the other, and pressed closely and perfectly by three 

 milled-headed screws in the brass bridge, which bear upon the 

 collar or ring of brass with their points. The degree of pres- 

 sure necessary is not to be very great, but it must be equably 

 exerted and felt on each screw, in order that the surfaces 

 should be applied truly, and that the joint may be air tight— 

 a very little practice will render this operation easy and certain. 

 The bridge with its screws, &c. is represented, fig. 4, a (PL 

 XIV.) — The plan of the bridge, and the end of the barrel 

 with the valve in the piston, is seen at (6). — (r) is a stop to 

 prevent the piece to be joined to the barrel from being pushed 

 too far. 



The glass valves are formed of plane convex lenses not 

 polished, fitted to hollow spherical cavities, as in figs. 5 and 6, 



These particulars being premised, the description of the 

 instrument v^dli be more easily understood. 



Fig. 1, (PI. XIII.) Represents a perspective view of the 

 glass condenser, mounted on its frame and stand. 



Fig. s, (PI. XIII.) A side view of the glass pieces of the 

 condenser, disencumbered of the frame and connecting col- 

 lars. The piston is seen outside of the barrel, and the iron 

 sliding bar, with its arms which support the barrel, is repre- 

 sented with its clamps — but without the mahogany pieces. 

 The same letters refer to the same parts of the instrument in 

 figs. 1 and 2. 



In figure 2 are also represented the valves in their places— 

 the joints connected by dotted lines are permanent. 



Us 



