58 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



potassium, sulfuric acid and water. The gas is slightly lighter 

 than air and is a most deadly poison. Its use is to be recom- 

 mended only by thoroughly competent and careful persons who are 

 fully advised as to the method of use for the particular purpose 

 desired. Concerning its use advice should be sought from the State 

 Agricultural Experiment Station, or from the State Entomologist, 

 or from the Bureau of Entomology of the U. S. Department of Agri- 

 culture. The general methods used are fully described by the late 

 Professor W. G. Johnson in his book " Fumigation Methods \ 

 (Orange Judd Co.), with which should be considered the results 

 of more recent experiments and experience. 



Sulfur Dioxid. The fumes of burning sulfur, mostly sulfur 

 dioxid, have long been recognized as a standard remedy for the 

 fumigation of dwellings and barracks for insect pests. Successful 

 fumigation for the bedbug has been reported when stick sulfur has 

 been burned at the rate of 2 pounds per 1000 cubic feet of space. 

 The chief objection is the strong bleaching effect of the fumes in 

 presence of moisture and their destructive action on vegetation. 

 Recently this gas has been extensively used under the name of 

 " Clayton gas," for the fumigation of ships and ships' cargoes, par- 

 ticularly grain. It is forced into the tight hold of a ship by special 

 apparatus and is exceedingly penetrating and effective. The 

 germinating power of seeds is quickly destroyed, but they are not 

 injured for food. 1 to 5 per cent of the gas, with an exposure of 

 twenty-four hours, is effective for most -seed and grain pests. It 

 cannot be used on vegetation or for moist fruits. 



Tobacco Fumes. Tobacco is extensively used as a fumigant 

 for aphides in greenhouses and for certain plants, such as melons, 

 by using it under covers. Several forms are now commonly 

 used. Tobacco or nicotine extracts are sold under various trade 

 names, which are volatilized by heating either with a small lamp 

 or by dropping hot irons into the dishes containing the fluid. 

 The same material may be purchased in the form of paper which 

 has been saturated with the extract and which is burned accord- 

 ing to directions, a certain amount being sufficient for so many 

 cubic feet of space, which forms a. more convenient method of 



