March 16, 1882 | 
than one molecule of lead peroxide, and the possibility 
of local action gradually diminishes as the reduction 
proceeds. 
All our other experiments told the same story as far as 
the absorption of hydrogen is concerned, but there are 
differences on the other plate. In one or two instances, 
not half of the theoretical amount of oxygen was ab- 
sorbed. On searching into the circumstances on which 
this depended, we were unable to arrive at any other con- 
clusion, than that it was connected with the condition of 
the surface of the lead plate. 
Experiments with a current of about two Ampéres 
showed that a larger quantity of both hydrogen and oxygen 
was fixed in a given time, but there was a larger propor- 
tionate loss, especially in the case of oxygen. Experi- 
ments with a current of about half an Ampére, on the 
contrary, gave a somewhat less rapid action, but a smaller 
waste of force through the escape of free gas. 
A complete study of the results of these experiments 
would be instructive, but the following comparisons may 
suffice to illustrate the points just mentioned. The theo- 
- retical amount of oxygen required for the red lead used 
is about 1200 cc., and the table shows the length of time 
in which 300, 600, and 1000 cc. were fixed by different 
strengths of current, together with the accompanying 
loss. 
NATURE 
Strength of Amount of 7 ‘ 
current. oxygen stored. Time. Loss of oxygen. 
Ampéres cc. hours. cc. 
2 300 15 174 
I ” 2 18 
3 ” 3 8 15 
600 4 617 
I ” 55 249 
2 ” 76 47 
2 1000 13°9 3081 
I ” 122 900 
4 cs 160 400 
In some cases we mixed the red lead with a little water, 
and allowed it to dry. In other experiments we mixed it 
at once with dilute sulphuric acid, but without any parti- 
cular practical advantage. 
The forming of a good secondary battery is a matter 
evidently depending upon very nice adjustment of condi- 
tions. It is but a few of these that we have carefully 
studied ; nevertheless we feel ourselves in a position to 
make one or two suggestions in regard to the economic 
aspects of the question. It is evident that the energy 
stored up in a cell is determined mainly by the amount of 
peroxide present. This appears to be obtained with the 
smallest amount of waste when the current is not too 
strong ; in fact, in our experiments it was obtained when 
the density of the current was about 6} Ampéres, cal- 
culated on the original surface of the lead plates. 
There would seem to be no commensurate advantage 
in continuing the current after the oxygen has ceased to 
be absorbed pretty freely, because the presence of some 
unoxidised sulphate of lead, although it increases the 
resistance, rather impedes than promotes local action. 
On the other hand, however, it is necessary that the 
reduction of the minium on the opposing plate should be 
complete, for a mixture of lead peroxide and metallic 
lead would be peculiarly conducive to the production of 
lead sulphate, and thus increase the resistance; while if 
any peroxide should remain, it would diminish the electro- 
motive force of the cell. ! 
It would appear probable, therefore, that the most 
economical arrangement would be obtained by making 
the red lead to be hydrogenated much smaller in amount | 
463 
than that to be oxidated. On trying the experiment with 
only half the quantity, we obtained a most satisfactory 
result as far as the charging was concerned. How far 
such an arrangement may be really desirable we hope to 
consider more fully when we treat of the chemistry of the 
discharge. J. H. GLADSTONE 
March 9 ALFRED TRIBE 
THE CHANNEL TUNNEL 
HE two schemes for a tunnel beneath the Channel, 
on the comparative merits of which a Parliamentary 
Committee will probably take evidence in the course 
of the year, are based, like those which have preceded 
them, chiefly on geological considerations. The Weald of 
Kent and the Bas-Boulonnais, once in all probability geo- 
graphically continuous, still constitute a single geological 
area. The chalk of Calais and Sangatte forms the pro- 
longation of that long range which, striking through 
Dover, Rochester, and Guildford, to near Basingstoke, is 
known as the North Downs; while that which strikes the 
coast south of Boulogne, is continued in Beachy Head, 
and the long range of the South Downs. The North and 
South Downs curve gently round, so as to meet towards 
the west, and similarly the Bas-Boulonnais is inclosed by 
the meeting of the two ranges on the French coast towards 
the east. 
In both these districts the beds of the chalk dip away 
from the inclosed area, generally at a gentle angle as at 
Dover, but sometimes steeply as in the Hog’s Back. It 
is clear from this that the beds which rise to the surface 
in the Weald and in the Bas-Boulonnais are geologically 
older than the chalk, and must pass under it laterally. 
The escarpments of the chalk may thus be compared to 
the fragmentary walls of an oval dome, the top of which 
has decayed away. The longer axis of this dome extended 
approximately east and west. 
The sequence of beds from the chalk downwards is as 
follows * :— 
English Bas- 
Coast. _ Boulonnais. 
dace are pee feet. 
x alk: with-flints) ... ss. «ss. 350 
WITS 5 Giaeiesrauhieea ats "130 
Compact nodular without flints 90 130 
Lower 4 Chalk without flints 50 
Grey Chalk 209 180 
Upper Greensand O-12 0-3 
Gault sis 100 30-36 
ower GreensanGign stn issu <b ene 25 O 123 
7 Weald Clay 350 
Wealden Beds } Hastings Beas ar 1150 100 ? 
Purbeck Beds ... ea etd a 400 
Portland Beds... 80 } ga 
Kimmeridge Clay ... 1070( 4% 2 
Coralline Oolite 550 ( Ses a 
Oxford Clay 60 ZA 
Of these formations the Chalk and Gault have been 
proved to run with remarkable persistency over a very 
large area, changing in thickness slowly and uniformly in 
ascertained directions. It thus was a matter of the ut- 
most probability that they would be found occupying their 
proper position relative to the other formations, and of 
their usual dimensions, in the narrow strip occupied by 
the sea. All doubts on this point were set at rest by the 
experimental soundings conducted by Sir J. Hawkshaw, 
and subsequently in greater detail by the French engi 
neers, MM. Lavalley, Larousse, Potier, and de Lapparen’ ; 
7,671 soundings were taken by these gentlemen, and 3,267 
specimens of the bottom were brought up, nearly all of 
which could be identified with certainty as belonging to 
one or other of the formations named above. A [geo- 
+ The thicknesses of the Chalk on the English coast are taken from the 
Geol. Survey Memoirs, vol. iv. ; those of the Bas-Boulonnais from the French 
Report of 1877, the thickness of the Lower Chalk being estimated by the 
position of the lowest beds of flint. ; ; 
2 There is some uncertainty as to the thickness of thes: div.sions. 
