Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

The absorp- tion of gases by liquids. this it is a simple calculation how much air he will usually require to keep the CO2 in his helmet from affecting him more than 3 per cent, would at the surface. Taking into consideration leakage* in the Navy pumps, this is found to be about 1.5 cubic feet per minute. This volume of air will be needed at all depths, so we can calculate the amount of air the pumps must take in at the surface to supply the diver with the requisite amount, and also the number of revolutions of the pump, which will give this amount. (For table, see page 97.) The diver need never fear a want of oxygen, since the deeper he goes the more oxygen does he receive at each breath. In the very deep diving he might be affected by an excess of the oxygen pressure, but as he is unlikely at these depths to be exposed to its action for any very long time, we may disregard the danger altogether. MaaU When a gas is in contact with a liquid on which it has no chemical action, it is absorbed by the liquid in amounts which are proportional to the pressures under which the gas is at the time. In the lungs we have the blood practically in contact with the air. In the air we have three important gases—oxygen, nitrogen, and CO2. Of these the nitrogen alone can remain and accumulate in the blood. It is not to be supposed that the oxygen and CO2 are not absorbed by the blood under pressure, but the oxygen is used up by the tissues, and the breathing pre- vents the pressure of CO2 from ever increasing, so that the only gas which accu- mulates in abnormal quantity in the blood when the diver is under pressure is the nitrogen. When gas is forced into a soda water bottle under pressure, the water ap- pears to be unchanged so long as the pressure is kept up, but the moment we re- duce the pressure, by taking out the cork, we see the gas come bubbling off the liquid. If we apply the analogy to diving, the diver is the soda water bottle, and his blood is the fluid in the bottle. As the diver descends, nitrogen under pressure is forced into contact with his blood. The blood takes up the nitrogen from the air. So long as he stays below under that pressure, his blood appears to be unaltered ; when, however, he rises, the excess of nitrogen that the blood has taken up begins slowly to bubble off ; if the blood were as fluid as water it would come off as rapidly as from the soda water. Fortunately for the diver the blood is a thickish, albuminous fluid, in which bubbles do not readily form, and, as far as we can see, it can retain about twice the amount in solution that water can keep at any given pressure. Every diver knows that it is quite safe to come up from a depth of from five to six fathoms to the surface as quickly as he likes ; the reason for this will now be easily understood, since at such a depth the blood has only twice as much nitrogen in it as it has on the surface, and therefore bubbles arc unlikely to form. If, however, the diver has been for any considerable time at, say, 30 fathoms, and then comes up quickly, it is almost certain that bubbles will form and cause serious symptoms. Not only is the air taken up by the blood, but the tissues of the body also gradually get saturated with it. In the case of the blood the saturation is very quick ; it is probable, indeed, that the blood leaving the lungs is always saturated * Unavoidable loss due to clearance, heat of compression, and piston leakage. I 6