1887.] Mr C. I. Burton on a Constant Daniell Cell. 357 
ends of the plaster plug are opposite the two tubes containing 
solutions. Immediately that the observations are completed, the 
tap is turned off, and so diffusion of the solutions completely pre- 
vented. The tap is made of the peculiar shape shown in the 
diagram, in order that it may only he turned in one direction, and 
so the possible transfer of a minute quantity of the one solution into 
the opposite tube is avoided. 
Several years ago Mr A. P. Laurie and I used this cell con- 
stantly for four months, and during that time it showed no change 
of E.M.F., as compared with a standard Latimer Clark, readings 
being made to three figures only. More recently Professor Ayrton, 
of the City and Guilds Technical Schools, London, very kindly 
undertook to compare this cell with a standard Latimer Clark of 
his own construction, and also with Fleming’s standard Daniell. 
The results of the comparison are given in the following table. 
E.M.F. of standard Latimer Clark is taken as unity. 
Date. 
Standard Flem- 
ing, E.M.F. 
Experimental 
Cell, E.M.F. 
Temperature of 
Room. 
Standard 
Latimer Clark. 
1886. 
f 07466 
0-7476 
18° -2 C. 
16°-9 C. 
May 13. 
t 0-7462 
0-7476 
9 9 
9 9 
on 
J 0-7505 
0-7485 
18 °*6 
16°-1 
,, AO. 
\0 -7500 
07489 
19° *6 
18° -1 
„ 31. 
0-7509 
17°-9 
16°-8 
Oct. 7. 
0-7456 
0-7468 
... 
16°-8 
