73 



present were aphis, mealy bug, white-tailed mealy bug, scale insects. 

 In this room was a collection of cool-house plants. A difference in the 

 proportions of water, acid, and cyanide will here be noticed. 



Results. — In the previous experiments it was found that although 

 there was always an excess of acid present, some of the hydrocyanic 

 acid was not liberated, owing to the fact, probably, that potassium sul- 

 phate was formed and became crystallized upon the surface before all 

 the potassium cyanide below was reached by the acid. For this reason 

 more water was added to hold the potassium sulphate in solution longer. 

 In this trial, however, there proved to be too little sulphuric acid to gen- 

 erate heat enough to rapidly liberate the gas, and hence some of the 

 potassium cyanide was not decomposed at the end of the fumigation. 

 Under these circumstances this trial was not wholly successful, as only 

 the aphides were killed. 



TRIAL VI. 



Conditions. — Place, camellia room; I oz. potassium cyanide, 2 oz. 

 water, and 1^ oz. sulphuric acid to 190 ft. of space (see table). 



Results. — This trial was satisfactory, as no plants were injured and 

 all insects were killed with the exception of the rose beetle. 



THE " DILUTE METHOD" OF USING HYDROCYANIC -ACID GAS FOR 



FUMIGATING GREENHOUSES. 



Last year we worked with what I am going to call the concentrated 

 method of using hydrocyanic-acid gas with results as previously 

 shown — some satisfactory, some unsatisfactory. 



The following will show the results of the "dilute method" of using 

 the gas for fumigating greenhouses* 



TRIAL I. 



Conditions. — Date, January 17, 1899 ; place, camellia room; 1 oz. 

 potassium cyanide, 1^ oz. sulphuric acid, and 2 oz. water to every 3,000 

 cu. ft. In this room, containing 6,190 cu. ft. of space, 2.06 oz. cyanide 

 of potash, 4 oz. water, and 3 oz. sulphuric acid were used. It was 

 fumigated at night about 6 o'clock, the room remaining closed until 

 morning. The following insects were present: greenfly, mealy bug, 

 Fuller's rose beetle. The plants in this room at the time of fumiga- 

 tion were, coleus, azaleas in bloom, heliotrope, ferns, hoya, jasminums, 

 polygala, hibiscus^ ericas, orange trees, camellias, cinerarias, oxalis. 

 The temperature went below 50° F. 



Results. — Upon examination it was found that no plants were injured, 

 and none of the insects save a part of the green flies. 



x See article by Dr. J. Fisher, American Gardening, October 29, 1898, and Circular 

 37, before cited. 



