262 Wisconsin Academy of Sciences , Arts and Letters. 
stray the electrical connection. 1 Thus both the outer liquid 
and that in the cell are stirred continuously. 11 is a resistance 
to regulate the current in the solenoid. It was found that in 
order to get good steady motion the hard rubber wheel W was 
too light. This defect was remedied by boring holes A through 
the wheel near its edge all around the circumference, and fill¬ 
ing these with lead. On the same axis with W was another 
wheel (not represented in the figure) of the same size and 
weight, which served to balance the apparatus and at the same 
time to operate the stirrers of a second osmotic experiment like 
that shown in the figure. Thus osmotic experiments could be 
performed in duplicate, using but one motor. The arrange¬ 
ment for making and breaking the current in the solenoids of 
course did not require duplication, since the same current could 
be sent through both coils in series. 
With this new apparatus the osmotic pressures of 0.125 nor¬ 
mal LiCl solution in pyridine and also of 0.125 solution of cane 
sugar in pyridine were measured, using vulcanized caoutchouc 
as the membrane and pure pyridine as the outer liquid. The 
0.125 normal solutions were selected rather than 0.25 normal, 
because the latter yielded a rather higher pressure than could 
be conveniently estimated with an open manometer. The pre¬ 
liminary results (above recorded) obtained with 0.25 normal 
sugar solutions without shaking do not indicate this, for the 
highest pressure observed was below 200 cm.; but it was found 
that by stirring this pressure could be about doubled. 
With the stirring apparatus described. Fig. 7, it, of course, 
takes much more time to set up each individual experiment for 
the arrangement is more complicated. The necessity of stirring 
in osmotic experiments was found out after a long series of 
preliminary tests made in the old-fashioned way without stir¬ 
ring, and so during the time left only a limited number of tests 
could be carried out. Working with pyridine, moreover, has a 
very depressing effect on the nervous system, it being impossible 
iThe arrangement was such that the slight heating effect produced 
by the current in passing through the solenoid was negligible, for the 
readings of the manometer did not change perceptibly after the cur¬ 
rent had been turned off and sufficient time allowed for any difference 
in tempearture to become equalized. 
