MECHANICAL METHODS OF DESTROYING INSECTS 29 



ashes and road dust, finely pulverized and sifted on young leaves 

 serve to drive insects to other clean leaves which should be 

 poisoned. Substances which are of little or no practical use as 

 repellents, for vegetable insects at least, are legion. Among 

 those for use as topdressings, or about the soil of the plants, 

 which do not commend themselves or which produce indifferent 

 results are : Bone dust, soot, coal dust, liver of sulphur, lye, ben- 

 zine, naphtha, naphthaline, alum water, salt, saltpetre, etc. 



Bordeaux mixture is one of the most valuable insect deter- 

 rents and is particularly useful for flea-beetles, leaf-beetles and 

 other foliage-feeders. Its value as a fungicide is too well known 

 for further comment. The formula follows : 



Into a 50-gallon barrel pour 30 gallons of water, and sus- 

 pend in it 6 pounds of bluestone in coarse sacking. Slake 4 

 pounds of fresh lime in another vessel, adding water slowly 

 to obtain a creamy liquid, free from grit. When the bluestone 

 is dissolved' add the lime milk slowly with water enough to 

 fill the barrel, stirring constantly. 



With insufficient lime the mixture sometimes injures the 

 foliage, and it should be tested with a solution obtained by dis- 

 solving an ounce of yellow prussiate of potash (potassium fer- 

 rocyanide) in one-half pint of water. If there be insufficient 

 lime in the Bordeaux mixture the addition of a drop or two 

 of this solution will cause a brownish-red color, and more lime 

 should be added until no change takes place when the solution 

 is dropped in. Use the Bordeaux mixture promptly, as it de- 

 teriorates on standing. 



Stock solutions of both the bluestone and lime may be kept 

 for any length of time. Make the stock bluestone by dissolving 

 in water at the rate of 2 pounds to the gallon. The stock lime 

 is slaked and kept as a thick paste. Cover both mixtures, to 

 prevent evaporation and keep the lime moist. For the 50-gallon 

 formula add 3 gallons of the bluestone solution to 50 gallons 

 of water, and introduce the stock lime slowly until there is no 

 reaction with the testing solution. — Galloway. 



