212 



For an empty vessel nothing is so satisfactory as the pot and pan 

 method of generating the gas. It has the following advantages; is 

 more rapid than any other, is cheaper, is more effective, and is equally 

 appKcable to the largest and the smallest vessel afloat. With a suf- 

 ficient number of pots and pans 3,500 pounds of sulphur can be 

 burned just as quickly as 100. Ten pounds of sulphur in each of 

 350 pots will be consumed just as quickly as will 10 pounds in any one 

 of that number, namely, in less than five hours, a fact which was 

 demonstrated over and over in the outgoing work in San Francisco. 



At the beginning of this work it was thought a 2^ per cent gas with 

 three hours' exposure would be sufficient. Practice proved, how- 

 ever, that this was not effective and the strength of gas was increased 

 to 3 per cent and the exposure to five hours which a test, extending 

 over twelve months and'embracing over 3,000 vessels, proved to be 

 ample. 



The best pot in which to burn sulphur is 6 inches deep, has a flare 

 of 6 inches — that is, the diameter at the top exceeds the diameter at 

 the bottom by that much, is from 16 inches to 24 inches in diameter 

 at the top and has four hemispherical legs about the size of half a 

 billiard ball. These pots when in use are set in a galvanized iron 

 tub. These tubs contain a httle water, and are of a diameter 6 inches 

 greater than the top of the pot. The hemisperical legs of these pots 

 will not punch holes into the tub. The pots are filled with sulphur, 

 which is hoUowed out into a Httle crater at the top, into which crater 

 from 4 to 6 ounces of alcohol are poured and when all are ready a 

 lighted match is dropped into each little crater and the compartment 

 is closed. 



In actual practice it was found that an exposure of five hours to a 

 3 per cent gas would not destroy all the rats in absolutely every case. 

 Some ships afford better hiding places than others, and on these an 

 occasional rat would escape. It was the custom, however, to fumi- 

 gate all vessels every thirty days and after the third fumigation, on 

 vessels that did not carry general cargo, no more rats were obtained, 

 though the fumigations were continued for a number of months. 



On those vessels that carried miscellaneous general cargoes a few 

 rats were found after almost every fumigation. These vessels 

 touched no wharf from the time they left San Francisco until their 

 return, except for a short time in Honolulu, where adequate pre- 

 cautions were observed, and it is difficult to understand how these 

 rats got on board if they were not carried on in cargo. 



For vessels with cargo in their holds the pot and pan method is 

 dangerous owing to the possibility of fire. For these vessels one of 

 the other methods of generating the sulphur gas must be used. This 

 involves the use of an expensive plant consisting of a furnace, cooling 

 chamber, blower, or fan, and a system of mains and delivery pipes 



