Kohlenberg—Osmosis and Osmotic Pressure. 261 
figure) as the stirrer moved downward, thus allowing the per¬ 
forated disc to come close to the membrane without actually 
touching it. These prongs of course do not interfere with the 
upward movement of the stirrer. The soft iron lug at the up¬ 
per end of the stirrer had a longitudinal groove (not shown in 
the figure) filed into it to facilitate the introduction of the 
liquid into the cell. After the glass part of the osmotic cell had 
been blown in one piece, the iron stirrer was introduced and the 
prongs bent into the required position; the membrane was then 
tied on and supported with cloth and steel disc as heretofore 
described. The proper quantity of mercury was then intro¬ 
duced and finally the cell was filled with the solution. A fine 
long funnel tube was employed in introducing the mercury and 
the solution into the osmotic cell. The upper end of the osnuv 
tic cell, through which the cell had been filled, was then drawn 
off before a blowpipe flame, as already described, so that prac¬ 
tically no air remained in the cell after it was sealed. The os¬ 
motic cell was mounted in the beaker as indicated in Fig. 7, 
the cork closing the cell securely, leaving only a little play for 
the stirrer F. 
Over the sealed end of the osmotic cell is placed the solenoid 
M; and by making and breaking the current in M, the stirrer 
in the osmotic cell is moved up and down. By means of the 
wires LL the small electric motor G is connected with a num¬ 
ber of storage batteries; the latter are not shown in the fig¬ 
ure. The motor G turns the wheel Yf, through the agency of 
a belt, and thus operates the crank 0 which moves the stirrer 
F. Now the wheel W is made of hard rubber and on it are 
fastened two small brass plates PP which are connected with 
each other by a wire. Mounted on separate supports, inde¬ 
pendent of the wheel W, are the two brass brushes DD, which 
make contact with PP. These brushes DD are connected with 
the source of current and the solenoid M by means of wires as 
shown in the figure. As the wheel W turns and the brushes 
DD come into contact with the brass plates PP on the wheel, 
the current in the solenoid M is established, the soft iron lug is 
attracted and the stirrer in the osmotic cell moved upward only 
to-be dropped again as soon as W has turned far enough to de- 
