EXPERIMENTS IN FUMIGATION. 273 



Preliminary tests showed us that this liquid does not volatilize 

 very readily at ordinary temperatures. Where large quantities 

 are used this is quite a serious objection, as it not only requires 

 a long fumigation period, but there is less certainty regarding 

 the period in which the effect of the full amount of material is 

 acting upon the scale and upon the trees. If trees with naked 

 roots are exposed for too long injury will result from drying. 

 It was suggested that this difficulty might be obviated by vola- 

 tilizing the liquid in heated pans. Therefore heavy cast iron 

 stew pans or "spiders" were used as generating dishes, these 

 holding the heat much longer than thin ones stamped out of 

 sheet steel. After heating to nearly 200° Fahr. one was placed 

 near each end of the box above the trees. Small holes through 

 the cover of the box enabled us to pour the liquid through a 

 funnel directly into the heated dish. The holes were stopped 

 with corks, and the carbon disulphide, which could be observed 

 through the glass in the cover, volatilized in a few seconds or 

 minutes, according to the quantity. Without the heated dishes, 

 several- hours were necessary in some cases. The quantities of 

 materials used, length of fumigating period, and the effect upon 

 scales and trees are given in Table I. 



Results with Carhon Disulphide. 



The smallest quantity used (10 fluid ounces per 100 cubic 

 feet) did not kill all of the scales in a fumigation period of one 

 hour. Where the heated dish was used to volatilize the liquid, 

 4.3 per cent, of the scales survived the treatment. Where the 

 dish was not heated 19.2 per cent, came through alive, but one- 

 third of the carbon disulphide was left in the dish at the end 

 of the hour, so that much less of the vapor really acted upon 

 the scales. All scales were killed in each of the other tests. It 

 is to be regretted that this small quantity of disulphide was not 

 given a two-hour period in one or more tests. One tree in 

 Experiment No. 3 failed to grow, but this probably has little 

 connection with the fumigation, as no other trees were injured 

 until they were given three times the amount of liquid and four 

 times as long a fumigation period. Moreover, untreated trees 

 often die when transplanted. When the liquid equalled or 

 exceeded thirty fluid ounces for one hour, some of the trees were 



