378 MANUAL OF VEGETABLE-GARDEN INSECTS 



deaux mixture of other strengths as recommended is made in 

 the same way, except that the amounts of copper sulfate and 

 lime are varied according to the requirements. 



It is not necessary to weigh the lime in making bordeaux 

 mixture, for a simple test can be used to determine when enough 

 of a stock lime mixture has been added. Dissolve an ounce of 

 yellow prussiate of potash in a pint of water and label it 

 "poison." Cut a V-shaped slit in one side of the cork so that 

 the liquid may be poured out in drops. Add the lime mixture 

 to the diluted copper sulfate solution until the ferrocyanid 

 test solution will not turn brown when dropped from the bottle 

 into the mixture. It is always best to add a slight excess of 

 lime. 



Sticker. 



The foliage of onions, cabbage and some other plants is so 

 smooth that it is difficult to make a spray adhere to it. The 

 following preparation will be useful for this purpose : 



Resin 2 pounds 



Sal soda (crystals) 1 pound 



Water 1 gallon 



Boil in an iron kettle in the open one to one and one half 

 hours, or until the liquid takes on a clear brown color. Add 

 this amount to each 50 gallons of bordeaux mixture. 



Fumigation. 



Two gases are in common use for killing insects, hydro- 

 cyanic acid gas and carbon bisulfid. The former is much used 

 for the destruction of vermin in houses, for fumigating nursery 

 stock and for the destruction of greenhouse insects, particularly 

 the white-fly and plant-lice. The latter is more generally used 

 for killing insects infesting seeds and tubers in storage. 



Hydrocyanic acid gas is generated by placing either potas- 

 sium cyanid (KCN) or sodium cyanid (NaCN) in dilute sul- 



