90 HYDEOCYANIC-ACID GAS FUMIGATION IX CALIFORNIA. 
Black scale. — When the black scale (Saissetia olex 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. 
