Dr. Hare on the Sliding- Rod Eudiometer ^ S)C. 171 



and which upon the whole appears to me the most probable. 

 It nearly corresponds with that of Dr.Wollaston (12'55), and 

 is much more convenient, on the scale, than its double as given 

 by Dr. Thomson. 



I am, gentlemen, respectfully, &c. 



John Phideaux. 



P.S. — I shall, with your permission, send a description of 

 the scale on another occasion : only adding here, that it is 

 double ; containing nearly five hundred substances : so dis- 

 posed as, with a little practice, to be as easy of reference as 

 Dr. Wollaston's, which in dimensions it nearly resembles. 



Plymouth, June 12, 1829. 



XXVI. On the Construction and Applications of the improved 

 Sliding-Rod Eudiometer and of the Volumescope. By Robert 

 Hare, M.D. of Philadelphia. 



[Concluded from p. 122.] 

 Description of the Volumescope. 



¥ N the following page there is an engraving of an instrument 

 (fig. 5.) which I have advantageously employed, in order to 

 illustrate the experimental basis of the theory of volumes, 

 and some other eudiometric phaenomena. 



As I find it very inconvenient not to have a name for every 

 variety of apparatus, I shall call this instrument a Volume- 

 scope. 



It consists of a very stout glass tube, of 36 inches in height, 

 and tapering in diameter inside from 2|^ to 1^ inches. The 

 least thickness of the glass is at the lower end, and is there 

 about fths of an inch. There is an obvious increase in thick- 

 ness towards the top within the space of about 6 inches. The 

 tube is situated between the iron rods 1 1, which are riveted 

 at their lower ends to a circular plate of the same metal let 

 into the lower surface of a square piece of plank. This piece 

 of plank supports the tube so as to be concentric with an aper- 

 ture corresponding with the bore of the tube, and constituting 

 efiectively its lower orifice. The upper orifice of the tube is 

 closed by a stout block of mahogany, which receives a disk of 

 greased leather in a corresponding hollow, formed by means 

 of a lathe, so as to be of the same diameter as the end of the 

 tube. Into a perforation in the centre of the mahogany block 

 communicating with the bore of the tube, a cock C, furnished 

 with a gallows screw, is inserted. Through the block on each 

 side of the ptrforution, wires are introduced so as to be air- 

 tight. To the upper end of these wires, gallows screws gg 

 Z 2 arc 



