for Washing Precipitales. 



97 



nothing of the difficulty, which, however, is by no means 

 slight, of bending the two concentric tubes; because all the 

 advantages, together with greater convenience for washing, 

 &c., may be obtained by having the tubes entirely distinct. 



The apparatus of M. Gay-Lussac, as described in Mohr 

 and Redwood's Pharmacy, is far superior to that now proposed 

 by M. Bloch, inasmuch as the air-tube does not communicate 

 with the fluid in the filter. The following contrivance has, 

 however, occurred to me as furnishing the most simple and 

 effectual way of attaining the object in view, and has the ad- 

 vantage of being applicable upon any scale of magnitude. 



It consists of a reservoir, fig. a, having the mouth placed at 

 its base. This, when 

 the vessel is filled with 

 water, is closed by a 

 cork, pierced by a 

 straight tube ^, pass- 

 ing through it ob- 

 liquely downwards. 

 It is now obvious that 

 the water will rise in 

 the tube b so long as 

 air can gain access to 

 the interior of the re- 

 servoir ; which, how- 

 ever, is prevented 

 when the water in the 

 tube is sufficiently 

 high to cover the 

 whole of its lower ex- 

 tremity. A siphon is then introduced through this tube so 

 as to project into the reservoir slightly beyond the lower ex- 

 tremity of the tube, care being taken to leave sufficient space 

 to allow of the passage of air between the siphon and the sur- 

 rounding tube. The funnel is placed beneath the long leg of 

 the siphon, so that the edge of the filter is a little above the 

 level of the water in the straight tube. In this condition the 

 apparatus works. As long as the level of the water in the 

 filter is lower than the level of that in the tube b, the column of 

 water ce will be heavier than the column cd, and consequent!}' 

 the siphon will keep up a supply of water, bubbles of air ob- 

 taining access to the interior of the reservoir, as the level of 

 the water in the tube b is reduced by the action of the siphon. 

 But no sooner does the water in the filter attain the same 

 level with that in the tube, than the column of water cd is 

 equal in pressure to the column ce, and consequently the action 



Phil. Mas. S. 3. Vol. 35. No. 234. Au". \s\-9. ' H 



