The ventilation system of the entire submarine is connected with certain chemicals, through which the air circulates, whose property is to absorb and retain the carbonic acid. Preparations of potassium are usually employed for this purpose. Simultaneously, cylinders of oxygen, under fairly high pressure, spray oxygen into the ventilation system, which is released in a measure proportionate to the number of the crew; there is a meter in the distributing section of the oxygen tubes, which is set to act automatically at a certain ratio per man. The ordinary atmosphere is bearable for a long time and this costly method of cleansing the air is used only as a last resort; the moment at which it must be employed is closely calculated to correspond, not only with the atmospheric conditions at the time of submersion, but also to the cubic quantity of air apportioned to each man according to his activities and according to the size of the boat.
It is unnecessary to clear the air artificially during a short submersion, but during prolonged ones it is advisable to begin doing so at an early hour to prevent the carbonic acid gas from gaining a disproportionate percentage, as it becomes then more difficult to control, and it is obvious that it is impossible to dissipate the fumes of cooking, the odors of the machine oil, and the breath of the crew.
Taken altogether one can live comfortably underseas, although there is a certain discomfort from the ever-increasing warmth produced by the working of the electrical machinery, and from the condensation created by the high temperature on the surface of the boat plunged in cold water, which is more noticeable in winter and in colder regions.
It is interesting to observe that the occupations of the crew determine the atmospheric conditions: the quantity of air required by a human body depends entirely on its activity. A man working hard absorbs in an hour eighty-five liters of air. Besides the commander, who is vigorously engaged in the turret,--as will be hereafter described,--the men, employed on the lateral and depth steering, and those handling the torpedo tubes, are doing hard physical work. The inactive men use up a far smaller quantity of air, and it is ascertained that a man asleep requires hourly only fifteen liters of air. A well-drilled crew, off duty, is therefore expected to sleep at once, undisturbed by the noise around them, and their efficiency is all the greater when the time comes to relieve their weary comrades. We had a wireless operator on board whose duties ceased after submersion, and he had so well perfected the art of sleeping that he never cost us more than fifteen liters of air, hourly, underseas.