L. MECHANICS AND ENGINEERING. 499 



deck. There is to be a cock in the main pipe near the gas 

 flask, and one in each branch pipe near the main, any one of 

 which can be turned from the spar-deck. 



On the alarm of fire the hatches are to be battened down, 

 the cock in the branch pipe leading to the compartment 

 where the fire is discovered is to be opened, and also the 

 cock in the main next the gas flask. The liquid gas, which 

 is under a heavy pressure in the flask, passes out through 

 the pipe in the form of vapor as soon as the pressure is re- 

 lieved by turning the main cock, and is driven in an instant 

 by the great pressure behind it to the compartment to which 

 it is admitted. Arrived at this point, and being one and a 

 half times as heavy as air, it fills the compartment from the 

 bottom up, without being diluted with the air, and produces 

 intense cold by its expansion at the same time; while the 

 pressure with which it enters forces it into all the interstices 

 in the cargo, driving out every particle of the air, which 

 will all escape from the top, as no compartment on board 

 ship is perfectly air-tight. Knowing, then, the cubic con- 

 tents of any compartment, and the cubic space occupied by 

 the cargo in it, sufficient gas can be admitted to render it 

 absolutely certain that no fire can exist there without the 

 necessity of opening the hatches to see if the fire is out, until 

 such time shall have elapsed as to render it perfectly safe 

 to do so. By shutting the cock in the main pipe the re- 

 mainder of the gas is kept from vaporizing until such time 

 as it may be required. 



On arriving in port, the flask is disconnected from its pipe 

 and sent to the gas manufactory, where it can be refilled in 

 a couple of hours, and on being returned is set up and con- 

 nected in its usual place. Should no fire occur, the appara- 

 tus can remain intact for an indefinite length of time, except 

 to see that the cocks are in working order occasionally. 

 The liquid is entirely non-corrosive in its character, and the 

 vapor is not injurious to any class of cargo, while it is, per- 

 haps, the only substance that will permanently suppress the 

 most advanced state of combustion in a cargo of coal. 



Lieutenant Barber remarks that, as is well known, car- 

 bonic-acid gas is the effective substance in the "Babcock" 

 and other patent fire-extinguishers, but in them it is produced 

 on the spot by the action of an acid on marble dust, or the 



