478 FRUIT INSECTS 



Formula B : Ounces 



Sodium arsenate (05 per cent) 8 



Lead nitrate 18 



Dissolve each salt separately in from 1 to 2 gallons of water ^ 

 (they dissolve more readily in hot water), using wooden vessels. 

 After solution has taken place, pour slowly about three fourths 

 of the lead acetate or nitrate into the sodium arsenate. Mix 

 thoroughly and test the mixture by dipping into it a strip of 

 potassium iodid test paper ^ which will turn a bright yellow if 

 lead is in excess. If the paper does not turn yellow, add more 

 of the lead salt slowly, stirring constantly, and test from time 

 to time. When the solution turns the paper yellow sufficient 

 lead salt is present, but if it should occur that the paper does 

 not turn yellow after all the lead salt has been added dissolve 

 a little more and add until an excess is indicated. The great 

 advantage of this test is that it is not necessary to filter the so- 

 lution or wait for it to settle. 



If the paper is not at hand, the test may be made by adding 

 a few drops of a solution of potassium iodid, when, if lead is in 

 excess, the instant the drops touch the solution a bright yellow 

 compound, lead iodid, will be formed. 



It is very essential that the lead salt be added in slight excess, 

 but a large excess should be avoided. 



If the material has been carefully prepared with a good grade 

 of chemicals, it will not be necessary to filter and wash the lead 

 arsenate formed, though it would be a safe precaution to allow 

 the lead arsenate to settle, then decant the clear solution and 

 discard it. Approximately 1 pound of actual lead arsenate 

 will be obtained by using the amounts of chemicals specified, 



1 The solution of lead acetate may have a milky appearance. This will be no 

 objection and it need not be filtered. 



2 If potassium iodid paper cannot be obtained it may be prepared by dissolv- 

 ing a few crystals of potassium iodid in about a tablespoonf ul of water and satu- 

 rating filter paper or blotting paper with this solution. After the paper has dried, 

 cut into strips and keep dry until needed. 



