eS ee 
April 19. 1883] 
NATURE 
583 
exercise of a common-sense check.” Too much weight may 
be attached to graphic statics, “but real utility is gained 
by making graphic methods a companion to (though not 
wholly a substitute for) analysis,’ and Prof. Minchin 
would assign a more conspicuous place to them in the text- 
books than they at present occupy. “Their essential 
merit consists in their furnishing visibly to the student 
the whole history of a magnitude throughout a series of 
variations in its circumstances.” Prof. Minchin would 
also banish such “crude” terms as “power,” “weight,” 
in the equilibrium of machines: such forces might be 
called “efforts” and “resistances.” Passing over one or 
two other subjects, we come to remarks on “illogical 
methods of teaching”; by such a method is here meant @ 
process which introduces considerations that are not essen- 
tially necessary for the purpose aimed at—considerations 
that can be seen a priort to be irrelevant. The moral is 
pointed by the discussion of a question of usual occur- 
rence in the text-books. The student should be able to 
be critic of his data, and “he ought to be taught to re- 
cognise clearly the object finally aimed at in any problem, 
and also to see what he must be given, and what he need 
not be given, in order to arrive at it.” For this purpose 
_ Prof. Minchin purposely uses with his students some 
books which, both in their data and in thetr methods, are 
full of illogicisms. The finale comes in pointing out the 
desirability of making the student carefully distinguish 
between the wezght of a body and its mass, and here he 
“comes down,” if we mistake not, on an episcopal writer 
of works on dynamics, for a “remarkable misuse of 
language.” 
(3) Prof. Lamb’s object is to suggest a new basis 
for the science of statics, and in the course of his paper 
he attacks certain principles and artifices, as “ the trans- 
missibility of force,” and (in hydrostatics) the solidifica- 
tion of matter, and also “rigid” bodies. The “point of 
departure” which he suggests is that “ the true and proper 
basis of statics is to be sought for in the principle of 
linear and angular momentum. Regarding statics as the 
doctrine of the equivalence of forces, I would define the 
word ‘equivalent, and say that two sets of forces are 
‘equivalent’ when, and only when, they produce the same 
effect on the linear and on the angular momentum of any 
material system to which they may be applied: ze. when 
they produce the same rate of change of momentum in 
any assigned direction, and the same rate of change of 
moment of momentum about any assigned axis.” He 
believes that on examination the objections arising from 
the supposed difficulty and abstruseness of this mode 
of treatment, “will disappear, and that ox ¢he whole the 
method will be found to be really much simpler than that 
at present in vogue. The main difficulty is at the outset.” 
A brief but interesting discussion followed, enlivened 
as it was by a friendly passage of arms over the term 
force of inertia. Roeele 
THE CHEMISTRY OF THE PLANTE AND 
FAURE ACCUMULATORS 
PART VE 
1. Jnfluence of Strength of Acid 
ile the second part of this communication in NATURE, 
vol. xxv. p. 461, when treating of the charging of the 
cell, we pointed out that in the electrolysis of dilute sul- 
phuric acid between lead electrodes, two totally different 
reactions might be obtained. The positive metal becomes 
thinly coated with lead sulphate when the current em- 
ployed is of small density, but with lead peroxide when 
the density of the current is of greater magnitude. This 
latter action is, of course, what takes place in the ordinary 
formation of a Planté battery. The chemical change, 
therefore, which goes on at the positive electrode is toa 
certain extent dependent upon the strength of the current. 
It appeared also of both theoretical and practical interest 
to determine whether the chemical change was also influ- 
enced by the strength of thc acid employed. Our experi- 
ments consisted in passing a current of uniform strength, 
about I ampere, between electrodes of lead, 12 square 
inches in size, in varying strengths of sulphuric acid, and 
estimating in each case the amount of oxygen fixed by 
the positive electrode. We determined this for successive 
five minutes of time, and as such actions are not always 
very uniform, we made in each instance more than one 
experiment. The results are given in the following 
table : — 
| | P f fixed 
BEE | sao | eee ee ereenlaee of onseenied 
of acid. | First Second {| Third | Fourth Total 
| | 5 mins. 5 mins. 5 mins. 2s mins. | “ips 
| Bate. eet 
| | 
etor5y || I 38°1 28°6 28°6 33°3 | 1286 
I 39'5 30°2 | 256 | 30:2 | 12575 
Ne i | 
| | | 
I to 10 I 43°4 38°7, | 29:2 34 145°3 
! 4471 39°3 29°3 349 147°6 
i} 
| fe 
I to 50 ls |) Ze 3) 39°6 35°3 22:4, || E4516 
Il. 46'2 43'9 23 30 143 I 
DIT.) | 54a eA Ome eS 563 35°5 | 165 
I to 100 Tony ea! 38°3 339 20°5 143°7 
II. 4274 40 378 BOS |) ESE y/ 
Ill. | 511 44°2 | 349 34°9 | 16571 
Ito 500, I. 46'6 32°6 27 27 132 6 
Il. |) 4674) 27 27 18 1184 
= oe ele 
Ito tooo I, 90°6 ED a 76°4 57°5 305°6 
| Il. go's | wa 72°3 63°1 
It appears from this that the strong sulphuric acid (1 
to 5) is not quite so favourable to the action as the more 
dilute (1 to 10), but that between this latter proportion 
and 1 to 500 there is no great difference in the amount of 
oxygen fixed, and therefore of corrosion of the plate. 
The appearance of the plate in every instance indicated 
the formation of only lead peroxide. With sulphuric 
acid diluted with 1000 parts of water, the amount of 
oxygen fixed, and therefore of corrosion, was at least 
doubled, while the chemical action was very different. On 
parts of the electrode, streaks of a mixture apparently of 
the yellow and puce-coloured oxides were seen. On other 
parts a white substance formed and was easily detached, 
falling in clouds into the liquid. Where this latter action 
took place, the plate was visibly the most corroded. This 
white substance gave on analysis SO, equivalent to 736 
per cent. of lead sulphate, suggesting the idea that it was 
a basic sulphate of the composition 2PbSO,,PbO, which 
would require 731 per cent. As the peroxidation of the 
lead is required, and the corrosion of the plate is to be 
avoided as much as possible, it is evident that this ex- 
tremely dilute acid must be avoided. It has already been 
shown that if the sulphuric acid is entirely removed from 
solution, as sometimes happens in an accumulator, the 
lead is simply converted into the hydrated protoxide, and 
therefore corroded without any good effect. 
2. Function of Hydrogen—In the formation of a 
secondary cell, after the complete reduction of oxide or 
sulphate to metallic lead, bubbles of hydrogen gas are 
seen to escape from the lead plate. It has been assumed 
that a portion of this is occluded by the lead, or in some 
other way enters into association with it, and it has been 
