EXPERIMENTS IN FUMIGATION. 277 



The sulphide of iron used is in the form of hard lumps made 

 by crushing the fused mass or slag. It is quite porous, which 

 facilitates the generation of the gas. It should be crushed fine 

 before use. Iron sulphide costs from eight to ten cents per 

 pound. 



Commercial sulphuric acid contains about ten per cent, of 

 water, and costs about five cents per pound in nine pound bottles. 

 Complete data regarding the tests with this gas appear in 

 Table III. 



Results with Sulphuretted Hydrogen. 



All scales were killed by this gas and some of the trees receiv- 

 ing the largest and smallest quantities died, though for some 

 inexplicable reason an intermediate amount produced no injury. 

 The method of generating this gas is too slow to render it a 

 convenient fumigating agent, even if it did not injure the trees. 

 Possibly some easier and more satisfactory arrangement could 

 be devised. 



Chlorine. 



Chlorine (CI) is a heavy • greenish gas with a pungent odor, 

 and is not only poisonous but extremely irritating to the mucous 

 membrane. It is about 2.5 times heavier than air, and is pre- 

 pared by treating ordinary chloride of lime or bleaching powder 

 with commercial sulphuric acid. Bleaching powder costs about 

 five cents per pound. 



Table IV. presents all of the statistics connected with the 

 chlorine tests. 



Results with Chlorine Gas. 



As perhaps might be expected with chlorine, all of the scales 

 were killed and most of the trees died also. This gas is alto- 

 gether too inconvenient, too disagreeable arid too destructive to 

 trees to be of any value in fumigating work. A peculiar effect 

 was noticed on those trees which survived the treatment. Nearly 

 all buds were killed, and the bark was injured and discolored 

 for half an inch or so each way from the bud, as if the gas 

 entered through the bud and damaged the surrounding wood. 

 The discoloration was apparent in some cases when the trees 

 were removed from the fumigating box. 



