320 GREENHOUSE MANAGEMENT. 



FUMIGATION WITH HYDROCYANIC ACID GAS. 



This is one of the most effective methods of destroy- 

 ing insects in the greenhouse and other places where the 

 air can be confined, but it should be used with the great- 

 est caution, as the fumes are fatal to all animal life. 

 Every precaution should be taken against the possibility 

 of anyone entering the house where the gas has been 

 used, until it has been dissipated. 



The gas treatment has for several years been used 

 for scale insects in California, but it was not until 1896 

 that it was used to any extent in greenhouses. It was 

 then tried experimentally, by Professor Galloway and his 

 assistants of the United States Department of Agricul- 

 ture, with very satisfactory results, as it cheaply and 

 effectually destroyed all the insects in the houses, includ- 

 ing several species that can be effectually reached in no 

 other way, without injury to most plants. The treatment 

 is, as yet, in its experimental stage, but it has progressed 

 so far that for many plants the amount that can be 

 used has been determined, and methods of producing the 

 gas, with the least risk and to secure the best results, 

 have been found. 



The houses should be tight, and so arranged that 

 the ventilators can be raised without entering the house. 

 The gas is produced by the action of sulphuric acid upon 

 cyanide of potassium in the presence of water. The 

 experiments show that for violets, coleus, many of the 

 ferns, Ficus elastica, crotons, etc., four ounces of chem- 

 ically pure (98 per cent) potassium cyanide, six ounces 

 of commercial sulphuric acid, and six ounces of water 

 can be used for each 1,000 cubic feet of space. Koses, 

 chrysanthemums and tomatoes are injured by this 

 amount, and further experiments are required to deter- 

 mine the exact quantity that can be used with safety. 

 It is also well to have a box in which cuttings and small 



