March 2, 1871 | 

NATURE 
351 

tion. They may be kept in a place convenient for observation 
by caging them ina vertical glass tube perforated sufficiently to 
secure equal density in the horizontal layers of liquid to be tested 
by the floaters. 
Anextemporised cell on this plan was exhibited to the Royal 
Society, and its resistance (measured as an illustration of Mance’s 
method, described in the first of his two previous communi- 
cations) was found to be -29 of an Ohm (that is to say, 
290,000,000 centimetres per second). The copper and zinc plates 
of this cell, being circular, were about thirty centimetres in 
diameter, and the distance between them was about 7°5 centi- 
metres. A Grove’s cell, of such dimensions that forty in series 
would give an excellent electric light, was also measured for 
resistance, and found to be ‘19 of an Ohm. Its intensity was 
found to be 1°8 times that of the new cell, which is the usual 
ratio of Grove’s to Daniell’s. Hence seventy-two of the new 
cells would have the intensity of forty of Grove’s. But the 
resistance of the seventy-two in series would be 209 Ohms, as 
against 76 Ohms of the forty Grove’s; hence, to get as 
powerful an electric light, threefold surface, or else diminished 
resistance by diminished distance of the plates, would be required. 
How much the resistance may be diminished by diminishing the 
distance rather than increasing the surface, it is impossible to 
deduce from experiments hitherto made. 
Two or three cells, such as the one shown to the Royal 
Society, will be amply sufficient to drive a large ordinary turret- 
clock without a weight ; and the expense of maintaining them 
will be very small in comparison with that of winding the clock. 
The prime cost of the heavy wheel-work will be avoided by the 
introduction of a comparatively inexpensive electro-magnetic 
engine. For electric bells, and all telegraphic testing and sig- 
nalling on shore, the new form of battery will probably be found 
easier of management, less expensive, and more trustworthy, than 
any of the forms of battery hitherto uced. For use at sea, it is 
probable that the sawdust Daniell’s first introduced on board the 
Agamemnon in 1858, and ever since that time very much used 
both at sea and on shore, will still be found the most convenient 
form ; but thenew form is certainly better for all ordinary shore used. 
The accompanying drawing represents a design suitable for 
the electric light, or other purposes, for which an interior resis- 
tance not exceeding 3, of an Ohm is desired. The zinc is in the 
form of a grating, to prevent the lodgment of bubbles of hydro- 
gen gas, which I find constantly, but very slowly, gathering upon 
the zincs of the cellsI have tried, although the solutions used 
have no free acid, unless such as may come from the ordinary 
commercial sulphate of copper and commercial sulphate of zinc 
crystals which were used. 
The principle which I have adopted for keeping the sulphate 
of copper from the zinc is to allow it no access to the zinc except 
by true diffusion. This principle would be violated if the whole 
mass of the liquid contiguous to the zinc is moved toward the 
zinc. Such amotion actually takes place in the second 
form of element (that which is represented in the drawing, 
and which is undoubtedly the better form of the two) every time 
the crystals of sulphate of copper are dropped into the charging- 
tube. As the crystals dissolve, the liquid again sinks, but not 
through the whole range through which it rose when the crystals 
were immersed. It sinks further as the sulphate of copper is 
electrically precipitated on the copper plate below in course of 
working the battery. Neglecting the volume of the metallic 
copper, we may say, with little error, that the whole residual 
rise is that corresponding to the volume of water of crystallisa- 
tion of the crystals which have been introduced and used. It 
becomes, therefore, a question whether it may not become a 
valuable economy to use anhydrous sulphate of copper instead 
of the crystals; but at present we are practically confined to 
the ‘‘blue vitriol” crystals of commerce, and therefore the 
quantity of water added at the top of the cell from time to time 
must be, on the whole, at least equal to the quantity of water of 
crystallisation introduced below by the crystals. Unless a cover 
is added to prevent evaporation, the quantity of water added 
above must exceed the water of crystallisation introduced 
below by at least enough to supply what has evaporated. There 
ought to be a further excess, because a downward movement of 
the liquid from the zinc to the level from which the syphon draws 
is very desirable to retard the diffusion of sulphate of copper 
upwards to the zinc. Lastly, this downward movement is also 
of great value to carry away the sulphate of zinc as it is generated 
_ in the use of the battery. The quantity of water added above 
ought to be regulated so as to keep the liquid in contact with the 

zinc, alittle less than half saturated with sulphate of z'nc, as 
it seems, from the observations of various experimenters that, the 
resistance of water semisaturated with sulphate of zinc is con- 
siderably less than that of a saturated solution. A still more 
serious inconvenience than a somewhat increased resistance hes 
been pointed out to me by Mr. Varley as a consequence of allowing 
sulphate of zinc to accumulate in the battery. Sulphate of zinc 
crystallises over the lip of the jar, and forms pendants like icicles 
outside, which act as capillary siphons, and carry off Jiquid. Mr. 
Varley tells me that this curious phenomenon is not unfrequently 
observed in telegraph batteries, and sometimes goes so far as to 
empty a cell and throw it altogether out of action. Even without 
this extreme result, the crystallisation of zinc about the mouth ot 
the jar is very inconvenient and deleterious. It is of course 
altogether avoided by the plan I now propose. 
In conclusion, then, the siphon-extractor must be arranged to 
carry off all the water of crystallisation of the sulphate of copper 
decomposed in the use of the cell, and enough of water besides 
to carry away as much sulphate of zinc as is formed in the use of 
the battery. Probably the most convenient mode of working 
the system in practice will be to use a glass capillary siphon, 
drawing quickly enough to carry off in a few hours as much water 
as is poured in each time at the top ; and to place, as shown in the 
drawing, the discharging end of the siphon, soas to limit the 
discharge to level somewhat above the upper level of the zinc 
grating. It will no doubt be found convenient in practice to add 
measured amounts of sulphate of copper by the charging-tube each 
time, and at the same time to pour ina measured amount of water, 
with or without a small quantity of sulphate of zinc in solution. 
As 100 parts by weight of sulphate of copper crystals contain, 
as nearly as may be, 36 parts of water, it may probably answer 
very well to put in, for every kilogramme of sulphate of copper, 
half a kilogramme of water. Experience (with the aid of spe- 
cific-gravity beads) will no doubt render it very easy, as a per- 
fectly methodical action involving very little labour, to keep the 
battery in good and constant action, according to the circum- 
stances of cach case. 
When, as in laboratory work, or in arrangements for lecture- 
illustrations, there may be long intervals of time during which 
the battery is not used, it will be convenient to cease adding 
sulphate of copper when there is no immediate prospect of 
action being required, and to cease pouring in water when little 
or no colour of sulphate of copper is seen in the solution below. 
The battery is then in a state in which it may be left untouched 
for months or years. All that will be necessary to set it in action 
again will be to fill it up with water to replace what has evapo- 
ratéd in the interval, and stir the liquid in the upper part of the 
jar slightly, until the upper specific gravity-bead is floated to 
near the top by sulphate of zinc, and then to place a measured 
amount of sulphate of copper in the funnel at the top of the 
charging: tube. W. THOMSON 


NOTES 
At the Anniversary Meeting of the Geological Society, 
held on the 17th ult., the Wollaston Gold Medal was presented 
to Prof. Ramsay in recognition of his many researches in prac- 
tical and in theoretical geology ; and the balance of the proceeds 
of the Wollaston Donation Fund was given to Mr. Robert Ethe- 
ridge in aid of the publication of his great. stratigraphical 
‘Catalogue of British Fossils.” A report of the interesting 
proceedings on the occasion will be found in another column. 
Mr. Prestwich was re-elected President of the Society for the en- 
suing year. 
A STATUTE was promulgated last week in Convocation at Ox= 
ford enlarging the powers of the delegates of ‘‘ unattached stu- 
dents,” whom it is proposed to allow to admit students after 
examining them in one of the subjects already permitted (¢<., 
Classics and Mathematics), “‘ together with some other subject re- 
cognised in the schools of the University” (¢.g., Physical or 
Natural Science). 
We are indebted to Harper's Weekly for some of the interest- 
ing notes on science in America, which we are able to furnish 
this week, in advance of their publication there. This magazine 
provides its readers with an important and interesting summary in 
each issue of the progress of science on that side of the Atlantic. 
