On the Employment of Carbon in Voltaic Combinations. 35 
72. Palm Squirrel, adult, {Scmrus palmarum). Dry; most 
commonly l-3692nd, extreme sizes l-4800th and l-3000th. 
In their own serum or in urine they seemed contracted, the 
corpuscles often cup-shaped, bent, or shrunk, ranging from 
l-4800th to l-4000th. Blood from a prick of the tail. 
73. Furnier’s Capromys, adult, {Capromys Furnieri). Dry; 
common diameters l-3530th and l-3429th. Extreme sizes 
l-4000th and l-3000th. Blood from a prick of the ear. 
74. Bandicoot Rat, adult, {Mas giganteus). Corpuscles in 
their own serum very irregular in size, most frequently 
l-4000th of an inch, and many from l-5333rd to l-3200th. 
There was evidently considerable shrinking of the corpuscles 
while under examination, as observed in several trials. In 
dried specimens the disks were generally from 1 -4000th to 
l-3600th. Extreme sizes l-4800tii and l-3200th. Blood from 
a prick of the tail. 
75. Hoary Marmot or Whistler, an old animal, (Arctomys 
pruinosa). Dry; most commonly l-3600th. Extreme sizes 
1 -4000th and 1 -3000th. Blood from a prick of the upper 
lip. 
Regent’s Park Barracks, Nov. 22, 1839. 
V. On the Employment of Carbon in Voltaic Combinations. 
By Mr. John Thoimas Cooper, Lecturer on Chemistry^ 
8^'c. 8^c. 
To Richard Phillips^ Esq., F.R.S., <^c. 
Dear Sir, 
T T occurred to me on reflecting upon the use of the platinum 
as employed by Mr. Grove in the construction of his 
very energetic voltaic combination*, as it was only to conduct 
the electricity from the decomposing nitric acid, that any 
cheaper substance which conducted electricity, and upon 
which nitric acid had no action, might be employed with equal 
advantage, and probably supply the place of the more ex- 
pensive material. With these views I was induced to make 
trial of charcoal, and the other forms of carbon, viz. plumbago, 
and a peculiar kind of carbon which is frequently met with as 
an incrustation in the retorts in which coal is decomposed for 
the purpose of gas lighting; and was gratified on making the 
experiments in finding my anticipations fully realized. In 
order to show the comparative value of each of the substances, 
I here subjoin the results of some of the experiments made 
with acids of the same strength, and with amalgamated zinc 
cylinders, each presenting to the action of the dilute sulphuric 
[* See bond, & Edinb, Phil. Mag., Oct. 1839, vol. xv. p. 287.] 
D2 
