110 INJURIOUS INSECTS OF 1903. 



26. Gum Camphor — (See Naphthaline.) 



27. Hellebore — 



This is an internal poison. It is used in place of Paris 

 Green in the case of cauliflower or cabbage when there is 

 danger of poison remaining on the part to be eaten. Hel- 

 lebore is not poisonous to man, and so can be handled 

 with impunity. 



For Currant Worms — Sprinkle the hellebore on the 

 leaves, on the under side when possible, when the dew is 

 on, or after the leaves have been sprinkled with water, to 

 insure its sticking. 



28. Hydrocyanic Acid Gas — 



It is fully recognized that fumigation with hydro- 

 cyanic acid gas is one of the best methods of combating 

 scale and other insects. For this reason many large nur- 

 series in the region infested with San Jose Scale fumigate 

 all their nursery stock before shipment. The laws of 

 some countries require this, while no nursery stock, ex- 

 cept evergreens, can be shipped into Canada without first 

 being fumigated with this gas at the port of entry. The 

 gas is now used in greenhouses, granaries, mills and other 

 buildings subject to infestation by insects or objectionable 

 animals of any. kind. The gas is a deadly poison to all 

 animal life and great care must be taken in generating it. 

 Unless thoroughly acquainted with its use, the entomolo- 

 gist or some competent authority better be consulted be- 

 fore handling. 



The chemicals used in the production of the gas must 

 be very accurately determined. The formula per cubic 

 foot of space usually used is : 



Potassium cyanide, 0.25 grammes; 



Sulphuric acid (98 per cent), one-half more acid, 



liquid measure, than cyanide ; 

 Water, one-half more water, liquid measure, than 

 acid. 

 I 



"The amount of cyanide necessary for any enclosure 

 is determined in terms of grammes per cubic feet of space 



