i88o.] 
On Water and Air . 
521 
that button and make contact with the battery, and you 
hear the noise of the explosion, and there you have the 
result. The bombshell is shattered to fragments, and re- 
duced to that state by the force of the shock that has been 
transmitted to the water. I do not know what is to be the 
future of this form of bombshell, but I can see that it is of 
very great importance. Now calamities in coal-mines often 
occur by the use of gunpowder, and it is possible — I will 
not say that it is certain — that by surrounding our charges 
of gunpowder with water in this way, we can do away with 
the danger that now is associated with the use of gunpowder 
in mines. 
I want to refer for a moment to the condensation of gases 
in so far as it bears relationship to that of vapour. You 
know that aqueous vapour is very easily condensed. It was 
long ago conjectured that the very air we breathe, and that 
oxygen, hydrogen, and nitrogen were the vapours of bodies, 
and that they could be congealed to a certain extent and 
reduced to a liquid condition. Various attempts were made, 
and various easily condensible gases were liquefied, but 
quite recently some of the more refractory gases have been 
condensed and rendered liquid by pressure. This has been 
done by two experimenters, Messrs. Cailletet and Pictet, 
working almost simultaneously. It is one of the cases in 
which we find the same thoughts on the same subject occur- 
ring to two different minds. Oxygen has been liquefied and 
nitrogen has been liquefied, and you know that the air we 
breathe is a mixture of oxygen and nitrogen. In 100 cubic 
metres of air there are 20 cubic metres of oxygen and 
80 cubic metres of nitrogen. I will not take the atmosphere, 
or oxygen, or nitrogen, because these gases require for their 
liquefaction appliances which we have not the means of 
using here ; but you remember the gas I brought before you 
in our first lecture,— the gas we obtained by the aCtion of an 
acid upon fragments of marble, — carbonic acid gas. This 
gas I intend to liquefy in the apparatus which is now before 
you (Fig. 42). B is a strong iron bottle containing mercury, 
into which is fixed a thick glass tube, p T. The end of the 
tube at P is closed, the lower end being open. This tube is 
held firmly in position by a strong iron nut, which is 
screwed into the bottle at n n'. Before introduction into the 
iron bottle, the glass tube was filled with pure carbonic acid 
gas. The tube w, which opens into the iron bottle, is con- 
nected to a powerful hydraulic pump. We will now urge 
water, by means of this pump, through the tube w, into the 
iron bottle, and force the mercury into the glass tube 
