562 
MR. W. C. D. WHETHAM ON THE ALLEGED SLIPPING 
recipe kindly given me by Dr. A. S. Lea. Each tube was dried and weighed, and the 
silvering solution then run through till a bright metallic mirror was deposited. It 
was washed out with a current of water, then with air, and finally dried and weighed 
again. The increase gave the weight of silver. At the end of the experiments with 
the tube thus silvered, it was again dried and weighed, and the silver dissolved off 
with nitric acid. The mean of these two results, which usually agreed to one or two 
tenths of a milligram, was taken to represent the weight of silver adhering to the 
tube during the experiments. • Assuming the deposit to be uniform, this at once 
gave the change in diameter. The correction for temperature was calculated hy 
Poiseuille’s formula. 
The first tube had a length of 37‘57 cms., and an average radius (determined by 
filling with mercury) of 0'0451 cm. 
The following series of experiments were made :— 
Temperature. 
Time of flow. 
18-2 
7 SO-S 
18-3 
7 50-4 
18-3 
7 50-6 
18-2 
7 50-4 
18-3 
7 51-0 
18-3 
7 51-0 
Means 18'26 
7 50-7 
The apparatus was then taken completely to pieces as it would he for silvering, and 
again set up after some hours, with the following results :— 
Temperature. 
Time of flow. ' 
o 
/ // 
17-8 
7 65-4 1 
17-9 
7 55-2 
If we correct this to 18°-26 by Poiseuille’s empirical formula we get T 51"‘0, a 
value identical with the above. The apparatus could thus be taken to pieces with 
safety. 
Weight of tube when dry.= 16'3916 grams. 
„ with silver.= 16‘3932 ,, 
