42 EEPORT OF COMMISSIONER OF FiSH AND FISHERIES. [40J 



and soldered, and though none of it is over No. 16 in thickness, it is 

 amply strong for the purpose. The polished registers are made to finish 

 with the joiner-work of the ship, and the pipes connecting them with 

 the conduits are, wherever possible, led behind the ceiling and other 

 joiner- work, and are quite out of sight. The fan is too well known, 

 commercially, to warrant a detailed description here ; it is sufficient to 

 say that it is a Sturtevant No. 6 centrifugal exhaust fan, and that the 

 ventilation of the ship is effected by drawing out the foul air, permitting 

 the fresh air to find its own way in, to supply the void, and is known 

 as the aspiration system. The motor, though one of the earliest forms 

 of steam-engine, bears a recent United States Patent Office date, and 

 is remarkable alone for its simplicity. It consists essentially of a short 

 hollow cylinder, its axis horizontal, containing a wheel in the circum- 

 ference of which there is placed a number of pockets or " buckets." The 

 "buckets^' just clear the surface of the cylinder, and revolve freely 

 within it; there are eight steam jets, arranged in such a manner that 

 the steam from them will impinge directly into the buckets and cause 

 the wheel to revolve upon its axis. The shaft of the motor extends 

 through and is also the shaft of the fan. The fan, according to the 

 figures of the builder, requires 2.86 horses-power to drive it 1,018 revo- 

 lutions per minute, at which velocity it should deliver 3,669 cubic feet 

 of air per minute. The quantity of air and the consequent size of fan 

 was determined from the experiments of the writer, on board the 

 United States ship Vandalia in 1879.* 



Let Q=the number of cubic feet of air to be supplied; %=the num- 

 ber of men; a=the cubic feet of carbonic acid exhaled per man per 

 hour (.0686) ; &=fraction of carbonic acid normal to the external at- 

 mosphere (.0004) ; c=fraction of carbonic acid found in the apartment. 

 Then 



7ia-\-Qh={Q,-\-na) e 

 from which we find 



na—nac 

 ^= c-b W 



From the experiments referred to we found the value of c to equal 

 .0006983. By substituting numericals for letters and deducing we 

 found 2,298 cubic feet per hour per man to be necessary.t The No. 6 

 fan, therefore, would be ample to ventilate for the 65 people who were 

 to compose the crew, and leave us a reserve of nearly one-third its 

 capacity for the hold of the ship, which we also provided with registers. 



It at once became a matter of interest to know what quantity of 

 steam was being used by the motor, and to ascertain, within reasonable 



* Proceedings of the Naval Institute for 1880. 



tThe chemical analysis of the air were made by Dr. Arthxir, of the Navy ; the writer 

 is responsible for the air measurements, the method, and the correctness of the cal- 

 culation. 



