Anti-rat measures to be observed by ship captains:
Destruction of rats on vessels.
Prevention of rats boarding a vessels.
To effect the destruction of rats on vessels the latter should be fumigated three or four times a year by sulphur burned in pots.
Almost any kind or size of iron pot will answer the purpose. The ordinary sugar pan 2½ feet in diameter is useful in disinfecting the hold of a vessel or a large compartment, the number of pans to be determined by the number of thousand cubic feet of area to be fumigated. Not more than 30 pounds of sulphur should be placed in each pot. For the fumigation of staterooms and the like the small iron cooking vessels are suitable. Each pot should always be placed in a tub of water, as shown in the illustration.
The tubs should be made of wood or compressed paper, as tubs made of galvanized iron or composition metal go to pieces rapidly through rust or breaks in the seams. The pots should never be placed on the floor of a compartment or bottom of the hold of a vessel. In compartments or storerooms they should be placed upon tables or chairs, and in the holds of vessels either on the "tween" decks, upon piles of ballast, or upon boxes. The sulphur should always be ground or mashed into a powder before being placed in the pots, and should be piled around the sides of the pot with a central depression or crater. Alcohol should always be used for lighting sulphur, although a hot coal will answer the purpose.
One pound of sulphur burned in a space containing 1,000 cubic feet will produce 1 per cent of the gas. Five pounds of sulphur burned in a space containing 1,000 cubic feet will produce 5 per cent of the gas.
On empty vessels burn 2 pounds of sulphur for every 1,000 cubic feet of space and let the gas stand for six hours.
In computing the capacity of the hold of a vessel for the purpose of determining the number of thousand cubic feet of space therein, and therefore the number of pounds of sulphur which will be required to produce a 2 per cent volume of the gas, the net tonnage of the vessel shows in a general way the cubic capacity of her cargo-carrying space. Ten net tons will represent 1,000 cubic feet of space; therefore, for every 10 net tons 2 pounds of sulphur must be used to get the average 2 per cent volume strength of sulphur gas. The capacity of the living apartments, storerooms, and the like had best be figured on separately.
In fumigating with sulphur gas all spaces must be made airtight. In fumigating the holds of vessels the hatches should be covered over with their regular waterproof tarpaulins and tightly battened down, leaving a small vent for the escape of the sulphur. All air slits, scuttles, and chain ports should be closed. The doors should be sealed by means of strips of paper pasted over the cracks left between the frame and the door.
If the vessel has cargo the killing of rats should be carried out under the direction of the nearest quarantine officer. After the fumigation is over the rats should be gathered (with the hands protected by heavy gloves) and burned in the ship's furnace or donkey boiler firebox, not in the galley.
Now, the important thing is to keep the vessel from becoming reinfested with rats. This is effected by (1) the use of rat funnels or guards on all lines while the vessel is in port, (2) by keeping a watch for rats attempting to walk up the gangplank, (3) by keeping a sharp lookout for rats being concealed in loosely crated freight, (4) by keeping the ship's food and stores carefully protected from rats, (5) by distributing rat poison (phosphorus or arsenic paste) in the vessel, (6) by keeping ship's cats (they should not be overfed, else they will not try to catch rats) , and, finally, by keeping rat traps constantly set
