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SCIENCE. 



[N. S. Vol. XIV. No. 347. 



port the cord above the jar by means of the 

 back of a chair or other convenient object 

 in such a position that when the load of 

 cyanide of potassium is attached it will 

 hang directly over the center of the jar. 

 Next weigh out upon a piece of soft paper 

 500 grams (about 17.1 ounces) of 98-per- 

 cent.-pure cyanide of potassium, using a 

 large pair of forceps for handling the lumps ; 

 wrap up and place in a paper bag and tie 

 to the end of the cord over the jar. After 

 the load for each jar has been similarly 

 provided, it is well to test the working of 

 the cords to see that they do not catch or 

 bind. Then remove the jar a short dis- 

 tance from under the load of cyanide and 

 place in it a little more than a quart of 

 water, to which slowly add one and one-half 

 pints of commercial sulphuric acid, stirring 

 freely. The action of the acid will bring 

 the temperature of the combination almost 

 to the boiling point. Replace the jars be- 

 neath the bags of cyanide, spreading a 

 large sheet of heavy paper on the floor to 

 catch any acid that may possibly fly over 

 the edge of the jar when the cyanide is 

 dropped, or as a result of the violent 

 chemical action which follows. Close all 

 outside openings and open up the interior 

 of the apartment as much as possible in 

 order that the full strength of the gas may 

 reach the hiding places of the insects. See 

 that all entrances are locked or guarded on 

 the outside to prevent persons entering, 

 then leave the building, releasing the cords 

 as you go. The gas will all be given off in a 

 few minutes, and should remain in the 

 building at least three hours. 



When the sulphuric acid comes in con- 

 tact with the cyanide of potassium the re- 

 sult is the formation of sulphate of potash, 

 which remains in the jar, and the hydro- 

 cyanic acid is liberated and escapes into 

 the air. The chemical action is so violent 

 as to cause a sputtering, and frequently 

 particles of the acid are thrown over the 



sides of the jar ; this may be prevented by 

 supporting a sheet of stiff paper over the 

 jar by means of a hole in the center through 

 which the cord supporting the cyanide of 

 potassium is passed, so that when the cord 

 is released the paper will descend with the 

 cyanide and remain at rest on the top of 

 the jar, but will not prevent the easy de- 

 scent of the cyanide into the acid. The 

 weight of this paper will in no way inter- 

 fere with the escape of the gas. 



At the end of the time required for fumi- 

 gation the windows and doors should be 

 opened from the outside and the gas al- 

 lowed to escape before any one enters the 

 building. A general cleaning should fol- 

 low, as the insects leave their hiding-places 

 and, dying on the floors, are easily swept up 

 and burned. The sulphate of potash re- 

 maining in the jars is poisonous and should 

 be immediately buried and the jars them- 

 selves filled with earth or ashes. ISTo food 

 that has remained during fumigation should 

 be used and thorough ventilation should be 

 maintained for several hours. After one of 

 our experiments it was noted that ice-water 

 which had remained in a closed cooler had 

 taken up the gas and had both the odor and 

 taste of cyanide. 



For dwellings one fumigation each year 

 would be sufficient, but for storage houses 

 it may be necessary to make an application 

 every three or four months to keep them 

 entirely free from insect pests. The cost 

 of materials for one application is about 

 fifty cents for each 5,000 cubic feet of space 

 to be treated. The cyanide of potassium 

 can be purchased at about thirty-five cents 

 per pound, and the commercial sulphuric 

 acid at about four cents per pound. The 

 strength of the dose may be increased and 

 the time of exposure somewhat shortened, 

 but this increases the cost and does not do 

 the work so thoroughly. In no case, how- 

 ever, should the dose exceed .22 gram or 

 remain less than one hour. 



