578 Agricultural Experiment Station, Ithaca, N. Y. 



little soluble arsenic is present, tlie sulplmret solution should be 

 warm when used, for the reaction is then more delicate. The sul- 

 phuret is easily made by anyone who has had even an elementary 

 instruction in chemistry, by adding sulphuric acid to iron pyrites. 



This sulphuretted hydrogen is not a commercial preparation, but 

 it is present in all sulphur mineral water, and the water may give 

 the test that I have described. One can always make sure of the 

 presence of this material, for its odor is strong and ofEensive. It is 

 the odor of spoiled eggs. If mineral water is used, it should be 

 strong and fresh and about equal in (quantity to the arsenic solution ; 

 and even then only a faint amber discoloration may appear, because 

 of the small amount of sulphur in the water. 



This test of arsenic determines only the fact that soluble arsenic 

 is or is not present. It does not determine how much soluble arsenic 

 there may be ; although the greater or less amount of the yellow color 

 on precipitation will afford a comparative idea of the amount present 

 in any two or more samples. 



I have already advised the use of lime with Paris green or Lon- 

 don purple for the purpose of taking up the soluble arsenic, by the 

 formation of arsenite of lime. If this is done, or if the Bordeaux 

 mixture is used with the arsenites, it will not matter if the poison 

 contain soluble arsenic. 



10. How can one determine if Paris green is pure ? — It some- 

 times happens that material which is obtained as Paris green con- 

 tains no arsenic. We once procured such a sample, which proved 

 to be chrome green. If the material is pure Paris green it will 

 quickly and completely dissolve in common strong ammonia, giving 

 a beautiful, rich, dark blue, clear liquid, whilst any of the com- 

 pounds which would ordinarily be substituted for Paris green on 

 account of their color and texture, will not behave in this manner 

 in ammonia. Any insoluble residue is imjDurity. Chrome green 

 will not dissolve in ammonia. 



11. What becomes of the arsenic lohen it falls ujpon the soil f — 

 With the action of the rain and the falling of the leaves most of the 

 arsenic which is applied to trees finally reaches the soil. What 

 then becomes of it? If lime has been used with the spray the 

 arsenic will be insoluble when it falls upon the soil. It is possible 

 that the organic acids in the soil, and also carbonic acid, may dis- 

 solve some of the arsenic, but it would be almost surely made im- 

 mediately insoluble again by combination with lime or other soil 



