90 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



Black scale. — When the black scale (Saissetia olese Bern.) is 

 partly grown, or before the insects become tough and leathery, 

 three-fourths of schedule A (Plate X) will be most economical for 

 use. However, when many of the insects are full grown or nearly so, 

 full schedule A (Plate IX) is recommended. The proper time to 

 fumigate for the black scale is while the insects are in the earlier 

 stages of development, i. e., before they become tough and leathery. 

 Exposure should be 1 hour if any eggs are present. Where only 

 young scales are present, 45 minutes is sufficient. 



COMPARISON OF SODIUM CYANID AND POTASSIUM CYANID FOR 



GENERAL FUMIGATION. 



A perusal of the discussion thus far ventured in this bulletin has 

 shown that the results with the use of a high-grade sodium cyanid 

 were equally as satisfactory as with a high-grade potassium cyanid. 

 A pound of the sodium cyanid contains at least one-fourth more 

 available gas than a pound of the potassium cyanid. Hence if we 

 pay one-fourth more per pound for the high-grade sodium cyanid than 

 for the high-grade potassium cyanid, the ultimate cost of fumigating 

 an orchard will be practically the same in either case ; or the cost of 

 potassium cyanid at 24 cents per pound is equivalent to sodium 

 cyanid at 30 cents. If sodium cyanid (124 to 130 per cent) does not 

 cost one-fourth more per pound than potassium cyanid (98 to 99 per 

 cent), there is an economy in the use of the former. At the present 

 prices in California potassium cyanid costs 25 to 25^ cents per pound, 

 whereas the sodium cyanid costs practically 28 cents per pound. 

 This means an economy of 2 to 3 cents per pound in favor of the 

 sodium cyanid. 



The writer recommends a 124 to 130 per cent sodium cyanid as 

 strongly as a 98 to 99 per cent potassium cyanid for fumigation 

 purposes. The sole question to decide between the use of these 

 two cyanids in any particular case is the cost. When it is considered 

 that the present manufacture of sodium cyanid is more universal 

 and greatly in excess of the potassium cyanid; that the sodium com- 

 pounds required in the manufacture of sodium cyanid are widely 

 distributed through the world, while commercial deposits of the 

 potassium compounds required in the manufacture of potassium 

 cyanid are largely confined to the German Empire; and that the 

 present unit price of sodium cyanid averages slightly less than that 

 of the other, it may be reasonably expected that at no very distant 

 time the sodium cyanid may be found supplanting the potassium 

 cyanid for fumigating purposes. 



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