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48
The watchman at the gangway is challenged and repeats his orders.
The warning notice is changed to show the present extreme danger.
A two-hour period for action of the gas is allowed.
Opening Out.—The skilled operators pull away the tarpaulins from the
hatches by means of the previously arranged quay ropes. They don the oxygen
apparatus and open out, as far as can be readily done, all sealed spaces and set
the windsails in the larger spaces.
An interval of 2 hours is allowed.
The operators again don the oxygen apparatus and search the ship for residual
fumes, each operator having with him a live animal as indicator. They declare the
ship free for the crew to board.
The apparatus is removed and emptied of residues.
Comment.—The operation is fraught with danger throughout.
The apparatus and care needed are excessive in comparison with the result
aimed at, if this be killing of rats.
This excess is proportional to the excessive demand of 3 lbs. to the 1,000 c. ft.
which has made the sulphur method somewhat destructive, especially in upperworks,
and has thus chiefly raised the question of HCN as an alternative. 3 lbs. of sulphur
burned in one thousand cubic feet is demanded ; this is three times the necessary
amount for rat killing in a well conducted operation and is more than three times
as destructive to paintwork, etc.
On its merits, sulphur reasonably used will continue as the prime fumigant.
The necessity for a close preparation of the ship is the same in both sulphur and
cyanide fumigation; success in either is proportional to the care taken in preparation.