132. TRANSACTIONS OF THE RoyAL CANADIAN INSTITUTE [VOL. XI. 
ture and is liable to leak out into the boat; it is poisonous and is capable 
of forming an explosive mixture with the air. Hence it is necessary to 
provide very vigorous ventilation when going on the surface. In the 
submerged condition the problem would appear to be even more diffi- 
cult. The available air gradually becomes vitiated, but it is found 
that the crew can live for several hours without any sort of air renewal 
or means of purification. This is due to the constant leakage which 
takes place from the compressed air system, a leakage which can never 
be entirely prevented. If desired, the carbonic acid, which gradually 
accumulates due to exhalation, may be removed by chemical means, 
or the foul air may be pumped out. Fresh air can be supplied from the 
compressed air reservoirs. There is, however, rarely occasion for re- 
sorting to such means. A greater difficulty is the escape of gasoline 
and poisonous fumes from the motor as well as from the battery. There 
is no convenient test for carbon monoxide suitable for use in submarine 
boats, whence it has been necessary to use white mice for indicating 
the presence of this poisonous gas to the effects of which these little 
animals are very sensitive. White mice breathe much more vigorously 
than human beings and will absorb carbon monoxide about twenty 
times as rapidly as man. Hence, long before man feels any discomfort, 
the mice will show symptoms of distress. When this occurs, and especi- 
ally when the mice become asphyxiated it is time to ascend to the 
surface and to renew the air in the boat. 
With proper precautions the crew may remain in the boat with all 
hatches closed for 12 hours or more, which is generally all that is required, 
since the boat can go to the surface as soon as darkness sets in. 
Life on board a submarine boat is, however, very fatiguing and for 
this reason the time in which a boat can stay away from its base is very 
limited. The crew has to be changed at frequent intervals or it must 
be given time to recuperate, a fact which in many cases may limit the 
practical endurance of the submarine boat more than the supply of 
fuel. As matters stand now it may be said that the crew of a submarine 
boat ought to be relieved after two or three weeks’ service. 
PROPULSIVE MACHINERY. 
For propulsion on the surface the gasoline motor was the first really 
successful engine. It was light, occupied small space as compared with 
the steam machinery and the combustion of fuel-oil was not more than 
about one-half pound per H.P. hour as against at least 14 lb. per 
H.P. hour for steam machinery with oil-fed boilers. For small boats, 
of a displacement of from 100 to 300 ts. where weight and space were 
very restricted, the gasoline engine offered the best solution, but the 
