62± Prof. H. A. Lehfeldt on the Electrochemical 
Results. 
(a) Coulometer for exact measurement. 
The electrolysing cell aud gas-burette as described are 
suitable for measuring quantities of electricity up to 800 or 
1000 coulombs : all the measurements can be made within 
ten minutes or so o£ the stoppage o£ the current, aud the 
quantity determined to within one-tenth per cent. Further, 
the apparatus can be got ready for use again by the manipu- 
lation of a few taps, instead of the tedious chemical processes 
required by the silver voltameter. 
If the gas be measured against that in a compensating 
bulb, as described by Hempel (' Gras-analysis '), the measure- 
ment is still more easy and rapid, though probably with a 
slight loss of accuracy. 
(b) Electrolysis of various Solutions. 
The quantity of gas given off was measured in the cases 
of :— 
Strength. 
Per cent, of 
Per cent. 
theoretic vield. 
HSO 
10 
99 
NaOH..... 
. 10 to 25 
98-5 to 99-8 
Xa o S0 4 ..., 
. 10 to 30 
Exact. 
XaX0 3 . . . , 
10 
53 (deposited sulphur). 
Xa'HPO, ., 
10 
97-5 to 99-7 
XaXrO, . . . 
10 
99-5 
KI" 
20 
62 (turned brown, and 
K.Cr.O 
5 to 10 
Exact. frothed). 
Xa C;0 4 . . . , 
Saturated 
91 (frothed). 
Xa" o HAs0. . , 
10 
97 
XaX0 3 .... 
10 
50 
XaCIO, .... 
10 
33 
It appears, therefore, that sodium sulphate and potassium 
bichromate are the best electrolytes to use in the coulometer ; 
no systematic differences could be detected between them, or 
between solutions of different strengths, or at different tem- 
peratures. There is, then, every reason to suppose that the 
electrolysis of these solutions is quantitatively correct. 
Sodium hydroxide, contrary to what is usually stated, does 
not seem to yield better results than sulphuric acid. 
. (c) Electrochemical equivalent of Oxygen and Hydrogen : 
value of the " Faraday." 
One "faraday"' of electricity (the amount associated with 
one gram-equivalent of matter) decomposes 9'0075 grams 
of water, vieMing 8 grams of oxvgen and 1*0075 of hvdrogen. 
