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THE MONTHLY BULLETIN. 



and the effectiveness compares favorably with that of the sulphur 

 fume methods. 



It was some time before the practice of exploding carbon disulphicl 

 became general; as a matter of fact, even at the present time indi- 

 viduals are encountered who are unfamiliar with the method. The 

 advantages and possible disadvantages have been treated by Professor 

 Burd in this issue, consequently reference is made to his contribution. 

 In leaving carbon disulphid this much should be said: That in our 

 experience this substance, together with the chemical combinations of 

 it sold under different trade names, are by far the best we know at the 

 present time, taking into consideration the economy in labor, time, and 

 materials, and in view of results obtained. 



Before laying aside vapor methods, it may be advisable to mention 

 distillate, gasoline and kerosene. When these explosive liquids are 

 ignited in a burrow they produce fumes which are known to be deadly, 

 just as are those exhausted from a gasoline motor. A possible advan- 

 tage is the cheapness of these products in comparison with carbon 

 disulphid by allowing a greater quantity for each dose, but use of them 

 has yet to prove a percentage of efficiency high enough to warrant their 

 general adoption. A patent vaporizer for distillate has been on the 

 market for a number of years, which has been approved by many. In 

 a few regions where peculiar soil types exist even the demonstrators 

 have admitted little success. During warm weather, when a cold ground 

 does not condense the vapor on the burrow walls, excellent results have 

 been observed, but unfortunately this is a time of year when the less 

 expensive poisoned grain does good work. During the winter it is 

 necessary to force a far greater volume of distillate vapor into each 

 burrow, and even then we are not assured that a vapor state of sufficient 

 duration will be maintained to keep the ground squirrel from reviving. 

 If it is necessary to repeat the operation too often labor charges will 

 eat into the low cost of operation which appears as an advantage in 

 the summer. Attendant danger of explosion is not serious in handling 

 the apparatus if necessary precautions are observed. 



There still remain numerous vapor and gas methods to be tested. 

 Perhaps the foremost of the remaining are hydrocyanic acid gas and 

 chlorine. Where fumigators of citrus groves have been at work using 

 either the cyanofumer or liquid cyanid process, dosages have been tried 

 out on squirrel burrows with satisfactory results. - The cyanid gas, 

 being lighter than air, could not be considered in this connection to 

 affect a 100 per cent cleanup unless considerable force can be placed 

 behind the charge. Rapid expansion of the gas upon release from the 

 liquid state might supply some pressure, whether sufficient is doubted. 

 Being lighter than air, cyanid gas might fulfill a requirement lacking in 

 carbon disulphid, namely, that of rising over some of the higher spots in 

 a burrow ; but would collect in these higher places unless forced on. We 

 know that killing by this gas is better in the tops of trees, giving good 

 evidence of the rapid rise of the vapor. Death would be practically 

 instantaneous, an advantage to be considered; still the combination of 

 the gas with moisture in the burrow and the high cost of operation would 

 detract to some degree from the possible use. Unless one lived in a 

 citrus district where materials were to be had on short notice or in. 

 quantity it would not be advisable to try. 



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