13 



Another formula proposed by Professor Kedzie, of Michigan, is as 

 follows : "Boil two pounds of white arsenic with eight pounds of sal 

 soda (washing- soda) in two gallons of water. Boil for 15 minutes in 

 an iron pot, or until the arsenic dissolves, leaving only a small amount of 

 muddy sediment. Put the solution into a two-gallon jug and label 

 'Poison — Stock Solution for Spraying Mixture.' The spraying mix- 

 ture can be prepared whenever required in the quantity needed at any 

 time by slaking two pounds of lime, and adding this to 40 gallons of 

 water ; pour into this one pint of the stock arsenic solution ; stir thor- 

 oughly and the spraying mixture is ready for use. The arsenic in this 

 mixture is equal to four ounces of Paris green." 



Other writers have recommended the use of larger quantities of 

 lime, even up to eight pounds instead of two to 40 gallons. The addi- 

 tional lime is used to prevent burning of the foliage. Larger quantities 

 of the poison solution may be used if desired. 



The mistake has been made in applying the soda stock solution of 

 arsenic without the addition of any lime. The arsenite of soda thus 

 formed is soluble and will burn the leaf, thus destroying the plant upon 

 which it is placed. 



The chief advantages of these calcium arsenite preparations are that 

 the materials are easily procured, it is easily prepared, it is cheap, and 

 it is a safe and reliable insecticide. 



The average wholesale price in original package quoted to the writer 

 for white arsenic is 8 cents per pound, and for sal soda 1 cent per pound. 

 It will thus be seen that the cost of the material required to make calcium 

 arsenite by either of these formulae is not excessive. 



Contact Remedies. 



As previously stated, these remedies are employed to destroy suck- 

 ing insects, which must be killed by contact. They kill by clogging the 

 breathing pores of the insects, and, to some extent, by their corrosive 

 action. To be effective, the plant or tree must be very thoroughly cov- 

 ered. In the case of the San Jose Scale, which may exist in a spot no 

 larger than a pin-head, one scale left untouched may produce as many 

 as a million offspring during the season. Consequently, thorough 

 spraying is essential to success. 



Sulphur. 



Sulphur is a yellowish, brittle substance which melts to a thin straw- 

 colored liquid at 114.5 C. and boils at 448. 4 C, changing to a brown- 

 ish yellow vapor. When these vapors strike a cool surface, they are 

 condensed and deposited as a fine amorphous powder, called "Flowers 

 of sulphur." It is this form which is useful for combatting insects and 

 for manufacturing the lime-sulphur washes. Sulphur also appears on 



