Description of an improved Hydro-pneumatic Apparatus. 249 



the metal of which the bridge is composed, taking into considera- 

 tion their respective situations. Thus in warm weather, when 

 the arch is expanding, the same would take place in the blocks, 

 which would raise the arch to a wider part between the abut- 

 ments; in cold weather the contrary would be the lase. The 

 arch bv this means would in all temperatures fit between the 

 abutments, obtaining from them that supj)ort which is necessary 

 to its stability, with a perfect uniformity in its thrust, or lateral 

 pressure. 



Your most obedient and very humble servant, 

 Chatham, April 1, 1820. I- K. K. 



XL. Description of an improved Hydro-pneumatic Apparatus. 

 By Mr. John Cuthbert*. 



y 113, St. Martin's-lane, London, April 13, 1819. 



Sir, — J. BEG leave to offer to the Society for the Encourage- 

 ment of Arts, Manufactures, and Commerce, a combination of the 

 blow- pipe and pneumatic trough invented by me ; the utility 

 and simple arrangement of which I hope will meet with their ap- 

 probation. 



It is a well known fact that in chemical analysis the blow-pipe 

 ii indispensably necessary; and the almost constant application 

 of the pneumatic trough need not be enlarged upon. The ap- 

 paratus I lay before the Society combines these two instruments 

 m one, and when required for either purpose, can at once, with- 

 out any trouble, be dismounted, and the pieces applied to their 

 separate uses. 



To a public lecturer, who often at the time of exhibiting the 

 effects of gas may have occasion for a blast-pipe, this combina- 

 tion is of infinite advantage, by reason of the facility with which 

 oxygen gas from a bladder may be introduced and passed through 

 the platina jet, which cannot be fused by the heat required. 



When the apparatus is used as a pneumatic trough, it is only 

 necessary to remove the mouth-pipe and cover ; which latter, 

 when taken off, becomes a useful tray for transferring the re- 

 ceivers from the pneumatic trough, the ledge of the cover being 

 sufficiently deep to contain water for that purpose. 



The water from the bottom vessel may be occasionally forced 

 up by the mouth, in case of a deficiency when many receivers are 

 in use, and is kept up to the height re(iuired by means of a 

 ■liding-pipe within the large tube J f; and if the contrary effect 



• From the Trantactions of the Society for the Encouragement of Artt, 

 Mamfacturet, und Commerce, vol. xvii. for 1819. The Soci«ty's silver medal 

 wa* presented to Mr. Cuthhert for this apparatus. 



Vol. 55. No. 264. April 1820. R is 



