Mr. V. Guthrie on a nau Form of Spirator. 65 



tube open at both ends, (/ is fitted, so tliat its lower end is a 

 little above the mercuiy, vi. The ui)])er end of ff is provided with 

 a cork, through which the siphon-tube / passes. In the second 

 hole of C the bent tube h is fixed, in such a manner that its lower 

 end dips beneath the surface of the mercury, m. Through the 

 third hole of the cork C a straight tube c is passed, whose office 

 is to convey water into the bottle A : the lower end of c is a little 

 above the mercury, m. Through the fourth hole in C a narrow 

 tube e is fastened, whose longer exterior limb dips under the 

 surface of the mercury 7i in the tube B. B is a small test-tube, 

 widened at the bottom in three directions, and containing a few 

 millimetres in depth of mercury, n. It is fastened with sealing- 

 wax to A, and is provided with a cork, the one orifice of which 

 admits the tube e; through the other passes the bent tube d. 



The lower extremity of the tube /being placed far down a 

 sink and a gradual stream of water being allowed to enter by c, 

 as indicated by (1), the water in A rises (2), the air is driven 

 out of A (3), bubbles througli the mercury n, and passes by d (4) 

 through the apparatus employed. During this filling of A mt\i 

 water, the mercury m prevents the retrograde flux of water 

 through h. After A is filled, the water rises in the tubes/ and 

 e until it reaches the top of/, when this tube acts as a siphon (5'), 

 and being wider than the ingress-tube c, gradually empties the 

 bottle A (G). To supply the place of this water the air must 

 eater by h (7'), and may thus be drawn through the apparatus 

 in use, while the mercury m in B prevents the regression of the 

 air through e. 



The instrument has of course a simpler form when required 

 to act only as an aspirator, for then the tube B and its append- 

 ages may be dispensed with. 



When an increased resistance has to be overcome (the instru- 

 ment being used either as aspirator or as expirator), the tube/ 

 is drawn further out of the tube (/. 



This form of spirator I have found to be certain in its action ; 

 for with a continuous stream of water, the volume of air which 

 passes througli is in definite proportion to the volume of water 

 employed ; and, indeed, the slower the stream of water the more 

 nearly equal arc these volumes, for in this case the amount of 

 water passing through c during the action of the siphon /is in- 

 considerable. 



Phil. Mar/. S. 4. Vol. 15. No. 97. Jan. 1858. 



