INSECTICIDES. 411 



out through the delivery tube. After the air was all out, 

 the delivery tube was stopped by a cork ; and, as the action 

 was still going on, the gas in the apparatus was under pres- 

 sure and remained so for thirty minutes, when the egg- 

 cluster was removed. No change could be detected, either 

 with the naked eye or by use of the microscope, and, by 

 March 24, about one-half of the eggs had hatched. On the 

 same date, nine other egg-clusters were treated in the same 

 manner, using the same apparatus under the same condi- 

 tions. An examination of the eggs failed to show any 

 change. These eggs hatched February 6. January 12. 

 Five egg-clusters were treated with hydrocyanic acid gas, 

 for thirty minutes, under a hood made by spreading oil- 

 cloth over three bottles. The edge of the cloth came down 

 to the .table, but not close enough to exclude the air, as there 

 were numerous crevices under the cloth. The density of 

 hydrocyanic acid gas, being .706, causes it to rise. The 

 egg-clusters were placed on a small card-board stand which 

 reached nearly to the top of the hood, which was punctured 

 several times, so that the gas might readily pass through. 

 Forty cubic centimeters of sulphuric acid were then added 

 to one-half ounce of potassic cyanide, the gas being passed 

 under the hood. No change was visible in the eggs after 

 this treatment, and nearly all of them hatched. January 12. 

 Five egg-clusters were treated with hydrocyanic acid gas, 

 under a hood made of wet unbleached cotton, the cloth being 

 drawn closely to the table and weighted down, so that no air 

 could pass under the hood ; with this exception, the process 

 and conditions were the same as in the preceding experi- 

 ment. Nearly all of the eggs hatched after being subjected 

 to this treatment. January 12. Ten egg-clusters were 

 treated with pure, concentrated hydrocyanic acid gas for 

 one hour. The apparatus consisted of three four-ounce 

 Florence flasks, marked A, B and C. Flask A contained 

 about one-half an ounce of potassic cyanide, B contained 

 concentrated sulphuric acid, and C the ten egg-clusters. A 

 was connected with B by means of a tube which dipped 

 below the surface of the sulphuric acid in B. The escape 

 tube from B passed through the stopper of C. There was 



