EXPERIMENT STATION BULLETINS. 489 



practice may be learned only by experience. If they sboulrl prove to be 

 so, it is likely that commercial companies mi^ht produce a crude extract 

 of houncing 'bet — incorporating it in lime-sulphnr concentrate, cheaply. 

 A single test extending over several months indicated that saponin, in 

 itself, did not cause lime-sulphur to deteriorate. 



b. FUMIGANTS. 



The advantage of the fumigaut — i. e. vapor or gaseous — contact 

 insecticides are generally recognized. Likewise, disadvantages are 

 equally well known. Generallv sDeaking. gases diffuse rapidly and 

 often penetrate where non-volatile liquids could never penetrate with- 

 out damage — as in stored grain, clothing, etc. Also many gases or 

 vapors are more rapidly absorbed by active insects than are any non- 

 volatile liquid insecticides. A disadvantage, such as difficulty of con- 

 fining a gas for tlie necessary period of time, may be overcome; but 

 danger from fire and explosion in the case of carbon disulphide, and diffi- 

 culty of application because of its danger to the operator in the case of 

 hydrocyanic acid gas are disadvantages never entirely eliminated. It 

 was in the hope of finding fumigauts which might be safely substituted, 

 in some cases, for the two fumigaut insecticides just named that test 

 work was carried on with ammonia and carbon tetra-chloride. 



Ammonia. Experience gained with ammonia as an insecticide, dur- 

 ing the time its influence upon the respiration of insects was being 

 studied, led to the belief tliat perhaps ammonia gas from compressed or 

 liquified ammonia might be applied as an insect fumigant with greater 

 ease and with less danger than hydrocyanic acid gas. Experiments car- 

 ried out with Calaiidra f/ramnia. Silvanus siiri)iamensis. and larvae of 

 Teuebroides mauritanicus enclosed with a little drv wheat in tight 

 glass receptacles showed that the insects could all be killed with three 

 to four per cent ammonia in twenty to twenty-two hours, and with nine 

 to ten per cent in six to seven hours. In fact, it was possible to kill in 

 most cases at loAver percentages, and in shorter periods when using the 

 higher percentages of ammonia — but death was always certain when 

 the gas was used at the rates given. 



A few germination tests were made with dry wheat treated with dif- 

 ferent percentages of ammonia, 100 grains being used in each check and 

 in each treated sample. It was found that where the percentage of am- 

 monia was kept up to about 3.2 for 22 hours the germination was ruined. 

 At 10 to 13.5 per cent for an interval of eight hours, however, fhe per 

 cent of injury from ammonia to germination was less than one; for ten 

 hours at 11.9 per cent the injury was over fifty per cent. 



Following the various laboratory tests, two fumigations of the college 

 mill-room were carried out with ammonia gas derived from cylinders of 

 compressed and partly liquefied ammonia. The room was closed as 

 lightly as any plastered room with closely fitting windows may be clos- 

 ed. The iron tube of ammonia was placed on a platform balance out- 

 side, and the ammonia gas was conducted through a tube (properly fit- 

 ted under the door) almost to the center of the room. Two wire cages 

 of insects were left in the open where they could be seen from the out- 

 side through the glass of the mill-room door. Two other cages were 

 buried three and six iuches, respectively, in dry wheat. There were 



