[Vor. 1 
40 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
of the silicic acid-hydrochloric acid mixture before dialysis is 
complete. А point of very great importance is the preparation 
of the collodion dialyzing bags. Ав has been pointed out by 
Kellerman (12), and others, the degree of permeability of the 
bags depends, in а large degree, upon the way in which they are 
made. Ifthe guncotton solvent is made from equal parts of ether 
and absolute alcohol, the bags will, in most cases, have a very low 
permeability, and coagulation of the enclosed silicic acid solution 
will frequently result before dialysis is complete. Тһе degree 
of impermeability is further increased by drying the bags 
rapidly. If, however, 95 per cent (instead of absolute) alcohol 
is used, and the bags are allowed to dry spontaneously by invert- 
ing the test-tubes in which the bags are being prepared in 
suspended wire baskets, a much higher degree of permeability 
will be obtained. 
Bags prepared with 95 per cent alcohol were used, and the 
silicic acid-hydrochlorie acid mixture dialyzed in tap water 
until the chloride content was no greater than that of the water. 
The вШсіс acid solution was further purified by dialyzing in 
changes of ordinary distilled water and finally in triply distilled, 
nitrogen-free water. In this extended dialysis, а considerable 
portion of the silicic acid is lost, and it usually becomes necessary 
to concentrate the solution to obtain a jelly of sufficient firm- 
ness. This is best carried out in heavy, two-liter suction-flasks 
in which the pressure is reduced until the solution boils at 
from 35 to 409С. If the concentration is carried out at higher 
temperatures, coagulation sometimes results. In order to pre- 
vent the violent bumping which always takes place unless some 
Special precautions are taken, it is only necessary to bring 
through the rubber stopper at the top of the suction-flask a 
glass tube drawn out at the bottom to a very fine capillary, 
which dips into the solution. Тһе top of this tube, outside of 
the rubber stopper, should be provided with a piece of rubber 
tubing and pinch cock to regulate the intake of air. Тһе air 
thus admitted may first be washed to remove carbon dioxide, 
ammonia, or other impurities. The concentration should be 
continued until a sample, when congealed, has the proper 
consistency. Тһе directions given by Smith (22) for coagu- 
lating the medium apply here and it need only be mentioned 
