PEAR GROWING IN CALIFORNIA. 295 



Fig. 105 shows a picture of the fumigating house of the Silva-Berg- 

 tholdt Nursery Company of Newcastle. The heavy door with padding 

 to insure against leakage in gas is clearly shown. The interior view, 

 Fig. 106, shows a platform erected midway between the floor and ceiling 

 to prevent too close packing of the lower bunches of trees from the 

 weight of bunches above with the possible interference with the diffu- 

 sion of the gas. This feature, while not absolutely necessary, is 

 desirable. 



In the larger nurseries a house of sufficient size so that a loaded wagon 

 or auto truck could be driven into the house and fumigated without 

 unloading the trees would be a decided advantage. 



Fumigation Process. 



An earthenware jar of sufficient capacity for the house is used as a 

 container for the chemicals which generate the gas. When the building 

 is packed with trees ready for fumigation the required amount of cya- 

 nide of potassium or cyanide of sodium, accurately weighed, is dropped 

 into dilute sulphuric acid of the proper amount. The proportions are 

 1 ounce by weight of cyanide of potassium, 1 fluid ounce of sulphuric 

 acid and 3 fluid ounces of water for every 100 cubic feet of space, or 

 f ounce by weight of cyanide of sodium, 1J fluid ounces of sulphuric 

 acid and 2 fluid ounces of water to every 100 cubic feet of space. 



Method. 



First measure the required amount of water and put it in the 

 generator, then measure the acid and pour it into the water. Never 

 reverse this process, as water poured into acid will cause a violent 

 sputtering which may injure the operator. The house should now be 

 tightly closed with the exception of one door near the generator. 

 Everything being in readiness, the cyanide of potassium or sodium, 

 according to which is used, is dropped into the jar and the remaining 

 open door quickly closed. The gas escapes immediately when the 

 cyanide is dropped into the generator and may be seen as a cloud 

 of vapor rapidly ascending to the ceiling. The house must be left 

 tightly closed for at least 45 minutes, and no injury will result to 

 trees from a one-hour fumigation. They should not be left in a longer 

 time than one hour. After 45 minutes to one hour have elapsed the 

 doors are thrown wide open and the gas escapes from the building 

 quite rapidly. 



Caution. 



Hydrocyanic acid gas, the product of the treatment of cyanide of 

 potassium or cyanide of sodium with sulphuric acid, is a deadly poison 

 and is fatal if inhaled in small .quantities unless very dilute. In 

 the open air there is little danger but when confined in a build- 

 ing where it is very concentrated one deep breath would almost 

 surely result in the death of the person inhaling. Therefore men 

 should never be allowed to remove trees from a fumigation house 

 until it has been aired fifteen minutes, or more. With ordinary 

 precautions the gas may be used with safety as attested by the gen- 

 eral fumigation of thousands of acres of citrus groves every season 

 with rarely an accident or a death from the inhalation of gas. 



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