MR. GROVE ON THE DECOMPOSITION OF WATER BY HEAT. 
5 
and novel apparatus for examination by voltaic ignition. It will presently be seen 
that my whole attention and disposable time were necessarily occupied with certain 
phenomena to which this class of experiments ultimately led me. 
Hydrogen gave a very notable contraction, amounting in some cases to one-tenth 
of its volume. This was an unexpected result, and I examined it with care. It took 
place both over water and over mercury ; rather more with the former than with the 
latter. It obtained equally with hydrogen procured by electrolysis from carefully 
distilled water and pure sulphuric acid ; with that procured from common zinc and 
pure sulphuric acid diluted with distilled water ; and with that obtained from distilled 
zinc and pure diluted sulphuric acid. The contraction was less when the water from 
which the hydrogen was obtained was carefully purged of air by boiling and the air- 
pump, but yet there was a notable contraction even when the water had been freed 
from air to the utmost practicable extent. In the numerous experiments which I made 
on this subject, the contraction varied from the y^th to the y^th of the whole volume. 
After many fruitless experiments I traced it to a small quantity of oxygen which 
I found hydrogen to contain under all circumstances in which I examined it. 
Phosphorus placed in hydrogen, obtained with the utmost care, gives fumes of 
phosphorous acid, shines in the dark and produces a slight contraction, but there is 
after this a further contraction by the use of the ignited wire. 
I may cite the following as an easy experiment and simple illustration of the 
rapidity with which hydrogen appropriates oxygen. Let hydrogen be collected over 
water well-purged of air ; let a piece of phosphorus remain in it until all combustion 
has ceased, the hydrogen will then be full of phosphoric vapour ; fill another tube 
with water, and pass the hydrogen rapidly into it, the second tube will instantly be 
filled with a dense white fume of phosphorous acid ; the hydrogen having instantly 
carried with it oxygen from the stratum of water it has passed. 
A very careful experiment was made as follows: — distilled water was boiled for 
several hours, to this was added one-fortieth part by measure of pure sulphuric acid, 
and it was cooled under the receiver of an air-pump ; it was now placed in two test 
glasses, connected by a narrow inverted tube, full of the same liquid : platinum elec- 
trodes were placed in each glass, and the hydrogen caused to ascend immediately 
into the eudiometer tubes; the whole was completed within two or three minutes 
after the water had been removed from the air-pump. Here the ordinary sources of 
impurity in hydrogen were avoided ; no zinc was used, the sulphuric acid was pure, 
and the quantity was so small, that, had it not been pure, the error could have been 
but very trifling. The hydrogen so obtained, contracted in volume -^ 6 -th ; hydrogen 
prepared in the same way, and exposed to phosphorus, gave dense white fumes ; the 
phosphorus was luminous in the dark for more than an hour, and the contraction 
(temperature and pressure being carefully examined) was ^th ; the amount of con- 
traction by the wire would of course equal three times the volume of oxygen mixed 
with the hydrogen, consequently the oxygen would be ^gth of the whole volume ; 
