EXPERIMENTS IN FUMIGATION. '275 



injured, and in some cases forty ounces for two hours killed 

 all of the trees, though in other instances some trees survived 

 even a larger quantity. It is quite possible that a longer period 

 with the smallest quantity would have given satisfactory results. 



Carbon Tetrachloride. 



Carbon tetrachloride (CCI4) is a clear, colorless liquid having 

 a specific gravity of 1.63 and a boiUng point of 169° F. It has " 

 a pleasant odor somewhat resembling that of chloroform, and 

 its vapor is non-inflammable and less poisonous than that of 

 carbon disulphide. Carbon tetrachloride is used chiefly as a 

 solvent and costs about forty cents per pound, though in quanti- 

 ties it can be purchased at a much lower price. Heated pans 

 were used to volatilize this gas, and the quantities used, fumiga- 

 tion period, and results are shown in Table II. 



Results with Carbon Tetrachloride. 



As carbon tetrachloride killed all of the scales in each of the 

 tests made, it is probable that even smaller quantities would have 

 answered quite as well. At the rate of forty fluid ounces per 

 100 cubic feet of space for two hours, some of the trees failed 

 to grow, and all larger quantities produced similar results. 

 Thirty fluid ounces appears to be about the maximum limit of 

 safety, and further trials should be made with smaller quanti- 

 ties of liquid and shorter periods of fumigation. As regards 

 convenience, this material is very promising, as it is not danger- 

 ously poisonous to breathe in small quantities nor liable to 

 explode, though more expensive than carbon disulphide. 



Gases Generated by Chemical Action. 

 Sulphuretted Hydrogen. 



Sulphuretted hydrogen or hydrogen sulphide (H2S) is an 

 invisible gas generated in our experiments from iron sulphide 

 and sulphuric acid. It is 1.19 times heavier than air. It has a 

 disagreeable and distinctive odor, and is very poisonous, although 

 on account of the odor its presence can be detected at once. Sul- 

 phuretted hydrogen is given off from spoiled eggs, and to some 

 extent from the lime and sulphur mixture. 



