IV. CONDENSATION ANT> SOLUTION OF GASES. 167 



in. OSMOSE, DIALYSIS AND DIFFUSION. 



631. Electric differential Osmometer. Engelmann. 



Prof. Engelmann, Utrecht. 



Two glass vessels of quadrangular section, possessing in the plane ground 

 surfaces facing each other a round aperture 30 mm. diameter, and each con- 

 taining an electrode ; a platinum disc 30 mm. diameter. Between the two 

 vessels the cell is placed, a plane parallel plate of ebonite, furnished with a 

 transverse perforation 30 mm. diameter, communicating with a short brass 

 top, upon which a rise-tube, manometer, etc. can be screwed. The mem- 

 branes or porous plates, whose electric osmotic permeability is to be compared, 

 are placed between the cell and the glass vessels, the whole being secured by 

 two brass vices. Both vessels and the cell are now filled with the same fluid. 

 Inelastic partitions, such as clay plates, must, in order to prevent breakage 

 and leakage, be provided, on each side, with an elastic ring (india-rubber or 

 bladder). 



Thin, \ery pliable, membranes, e.g. skin of a frog, are secured between sieve- 

 like perforated plates of ebonite to prevent bending. 



The apparatus is used to demonstrate : 



1st, the fact of electric osmosis. 



2nd, the specific influence of the membrane ; the rise and fall of the fluid 

 in the cell shows which of the two membranes possesses the greater electric 

 osmotic permeability. On removing one of the partitions, the apparatus 

 becomes an ordinary osmometer. 



(Onder/oekingen gedaan in het physiologisch laboratorium der Utrechteche 

 Hoogeschool. Derde Keeks, II., 1873, p. 365, etc.) 



632. Osmometer, illustrating the transpiration of gases 

 through capillary tubes. Prof. IV. F. Barrett. 



This is an apparatus constructed under the direction of Professor Sullivan 

 for illustrating the law of the transpiration of gases. The diaphragm is 

 made of a number of short lengths of capillary tubes. 



IV. CONDENSATION AND SOLUTION OF GASES. 



633. Addams' Apparatus, for condensing and solidifying 

 carbonic acid. William Sykes Ward. 



634. Apparatus used in 1857 for Liquefying Ice by 

 Pressure at temperatures below 65 C. 



Prof. Mousson, Zurich. 



A small cylindrical chamber, hollowed out of a strong piece of steel, is 

 filled with water containing a movable metallic index. When the water is 

 frozen, the chamber is closed by means of a soft copper cone, subject to the 

 action of a strong screw. The apparatus is then reversed. The chamber 

 merges into a long, slightly widening cone of soft copper, on which a short 

 steel rod presses by means of a powerful screw-nut acting on the principal 

 piece, and a double lever a metre in length. If the chamber be opened, after 

 the pressure is removed, the index is found to have been carried over to the 

 other end, as a proof that the ice has been reduced to a liquid state. Soft 

 copper is the only means of closing under excessive pressures. 



The experiment can be successfully made at 18 C. 



