PRODUCED BY BODIES ACTING BY CONTACT. 3 
: reduction are separated by the water which necessarily prevents 
their agglomeration. A volume of one cube inch filled with glo- 
bules, which we will suppose for greater facility not to exceed 
Tooswooth of an inch in diameter, but arranged so that lines 
passing through their centres are mutually perpendicular or 
parallel, will present a surface of 218,166 square feet. In 
every other position the surface would still be increased if they 
touched ; it is possible that platinum black offers a surface of 
this extent. 
Charcoal is best adapted for investigating the action of large 
surfaces on gases, and the experiments of Saussure on this sub- 
ject are of the greatest importance. Vegetable fibre does not 
fuse when ignited with care, so that the charcoal resulting from 
its calcination still preserves the form of the fibre; this is very 
ey dent, for when a carbonized section of wood is placed under 
the microscope, the walls of the cells are found to have remained 
intact. 
The cells of charred wood are on an average z;',5th of an inch 
in diameter; their surface would therefore be equal to 100 
square feet, supposing the charcoal itself to occupy no space. 
I prepared a piece of charcoal, which weighed 0°9565 grm., by 
boiling it for some time with pure water, and then simply wiping 
its surface ; it now weighed 2°2585 grms., and under water 0°110 
grm. The space which the water had occupied, and which con- 
sequently elastic fluids might enter in their turn on the expul- 
sion of the water, would amount then to five-eighths of the entire 
volume of the charcoal; taking into account the space occupied 
by the charcoal itself in order to calculate the extent of the 
surface, this does not amount to more than 73 square feet. 
Saussure found that charcoal absorbed thirty-five times its vo- 
lume of carbonic acid at 12°C. and at a pressure of 26°895; 
but these 35 volumes of carbonic acid are contained in the space 
which forms five-eighths of the total volume of the charcoal, 
and consequently fifty-six times less than the space originally 
occupied by the carbonic aeid. 
_ According to the experiments of M. Addami, carbonic acid 
becomes liquid at a pressure of 36°7 atmospheres, the tempera- 
ture being 12° C.; we are therefore led to conclude that more 
than one-third of the carbonic acid condensed in the pores of 
the charcoal is in a liquid state on the walls of the cells. 
If 35 square inches of carbonic acid are condensed on a sur- 
B2 
