PHYSIOLOGY: A. G. MAYER 721 
The results for the atomic weight of tin are arranged in the order in 
which the fractions were distilled, not in the order of analysis. Since 
only sKght irregular variations are apparent, there can be little question 
that the different portions were identical in composition. 
The final average, Sn = 118.703 (CI = 35.457) is in very close agree- 
ment with the one obtained by Briscoe by comparison with silver, 
118.698. The percent of tin in stannic chloride found by us is 45.562, 
while Briscoe found 54.439% of chlorine. The sum is 100.001%, a 
highly satisfactory and convincing outcome. 
It is a great pleasure to express our gratitude to the Carnegie Insti- 
tution of Washington and to the Elizabeth Thompson Science Fund 
for very generous assistance in providing indispensable apparatus. 
1 Trans. Chem. Soc, 107, 63 (1915). 
2 Ber. D. Chem. Ges., 21, 2900 (1888). 
' Baxter and Hartmann, /. Amer. Chem. Soc, 37, 113 (1915). Baxter and Grose, Ibid., 
38, 857, 868 (1916). 
* Baxter and Hartmann, these Proceedings, 1, 26 (1915). 
FURTHER STUDIES OF NERVE CONDUCTION IN CASSIOPEA 
By Alfred Goldsborough Mayer 
DEPARTMENT OF MARINE BIOLOGY. CARNEGIE INSTITUTION OF WASHINGTON 
Read before the Academy, November 13, 1916. Received, November 22, 1916 
Studies of recent years have shown the importance of hydrogen ion 
concentration in determining the rate of nerve conduction in Cassiopea. 
Ordinary distilled water often remains acid even though air freed from 
CO2 by means of soda-lime has been bubbled through it for 72 hours. 
Accordingly, Prof. George A. Hulett kindly arranged to have 144 litres 
of distilled water prepared in accordance with his well known method 
(Ueber die Reinigung des Wassers durch Distillation, Zs. phys. Chem., 
21, 287, 1896) in his laboratory at Princeton University. This water 
was sealed in 144 pyrex glass flasks and thus transported to Tortugas. 
The hydrogen ion concentration of each flask was tested separately, 
the range being 0.8 to 1.0 X 10"^, and the average being 0.9 X 10"^ 
or 6.04 PH. 
Fifty litres of this water were placed in a green glass carboy which 
had previously held Merck's distilled water; and air freed from CO2 
was bubbled through it at an active rate for 78 hours, after which the 
water in the carboy had a PH. of 8.0 which it maintained for eight days 
while 139 experiments were made with it. The alkalinity then declined 
to 7.5 PH. while 26 other experiments were made; the average for the 
