1913] CURRENT LITERATURE 445 
freezing point method uses weight normal, whereas the plasmolytic method 
uses volume normal solutions. He shows conclusively in his discussion that 
it is the plasmolytic method which has been in error. 
The large error of the old method is illustrated by the cryoscopic measure- 
ment of a volume normal cane sugar solution. The depression of the freezing 
point is —2.66° C., which indicates an osmotic pressure of 32 atmospheres 
instead of 22.4 atmospheres. The excess pressure is due to the sugar bei 
dissolved in less than 1000 cc. of water. A comparison of the pressures for 
67 per cent cane sugar and 18.5 per cent NaCl as calculated from the volume 
normal and weight normal concentrations is very illuminating also. e NaCl 
solution contains 3.6 moles of salt, so per cent ionized, in a liter of solution; 
while the sugar solution contains only 2.6 moles, with no ionizing, per liter. 
The NaCl should develop a much higher pressure according to the plasmolytic 
method of estimating pressures; but adopting the method of Morse, now 
shown to be correct, which demands equal quantities of solvent, we find that 
the NaCl is dissolved in 928 cc., the sugar in only 439 cc. of water. The rela- 
tions of the two solutions are seen to be actually the reverse of what the plas- 
molytic method indicates. Owing to the dissociation of the NaCl, the solutions 
are really nearly isosmotic. These examples serve to show the unreliability of 
the plasmolytic determinations with vol 1 solutions, and tl! ssity 
despite their inconvenience, of using weight normal solutions in the future. 
It is unfortunate that the physical chemists have not determined the 
osmotic pressure of saturated solutions by the cryoscopic method. ile 
RENNER makes clear that at the concentrations thus far measured the freezing 
point determinations will give the correct osmotic pressure, it remains to be 
demonstrated that this holds for all concentrations whatsoever. The direct 
determinations by Lord BERKELEY and HARTLEY for concentrated sugar 


If the cryoscopic methods should yield 
results in agreement with the direct measurements at these same concentra- 
tions, and with saturated solutions of various salts, its universal application 
could be admitted. If it does not, then still further correction of the formula 
for calculating the osmotic pressure of solutions must be made. “si 
physiologist interested in the determination of osmotic pressures should by a! 
means read RENNER’S excellent discussion.—CHARLES A. SHULL. 
Paleobotanical notes.—ARBER! has described 44 species of i. “a 
coal-field in Gloucestershire, none of which are new to Great eS 
‘Arper, E. A. Newett, On the fossil flora of the Forest of sy ngland and 
(Gloucestershire), and the relationships of the coal-fields of the west 0 
South Wales. Phil. Trans. Roy. Soc. London B 202:233-281. pls. 11-13: 1912. 
