igo6.] Fumigation by Hydrocyanic Acid Gas. 371 



The sulphuric acid should be poured very carefully into 

 the water, which may be put in an earthenware dish. The 

 cyanide of potassium, wrapped in blotting paper, should then 

 be dropped into the now diluted sulphuric acid. The dish 

 into which the cyanide is dropped must be so near the 

 door that it can be reached by the outstretched arm of the 

 operator, who should immediately shut the door and close up its 

 chinks by paper previously prepared. Another method is for 

 the operator to introduce the cyanide to the diluted sulphuric 

 acid through a window in the room or conservatory, the cyanide 

 being placed at the end of a long stick or rod, or being lowered 

 into the acid by a string and pulley. The window must be 

 closed immediately after the addition of the cyanide, so that 

 the operator may escape the fumes. Strawson recommends the 

 pouring of the diluted acid over the cyanide by arranging for 

 the purpose a bottle, which can be tilted up, containing the pro- 

 portion of acid. 



It is of importance that the hydrocyanic gas fumes be dis- 

 tributed over the house, and to diffuse them Strawson suggests 

 an arrangement of fans that could be worked from the outside 

 by a string. 



Fumigation should take place in the evening, or after night- 

 fall, and not in strong sunlight. The temperature of the house 

 should be from 50 degs. F. to 60 degs. F. The plants to be 

 treated should be dry. The surface of the soil of the house 

 should also be as dry as practicable. Experiment has shown 

 that the eggs of the Woolly Aphis may remain unaffected, and 

 therefore fumigation should be repeated in ten days. 



Points to be Carefully Noted. — The work should be done by a 

 careful and skilled operator. 



The cyanide and its fumes are very poisonous and dangerous 

 to human and other animal life. 



The treated room or conservatory must be kept closed during 

 fumigation from three-quarters of an hour to an hour, after 

 which the room should be ventilated, the windows, &c., being 

 opened from the outside^ and no one should enter until an hour 

 has elapsed. While opening the windows, &c , the operator 

 should be careful not to inhale the escaping fumes. 



It is safer not to fumigate when the plants are in bloom. 



G G 2 



