40 INJURIOUS INSECTS OF 1903. 



Minneapolis, June 19, 1903. 

 Fred L. Lavanburg, 18-20 River St., Chicago, 111. 



Dear Sir: I hereby certify that I purchased upon the open market an 

 original sealed package of the "Fred L. Lavanburg Paris Green" and 

 that I have analyzed the same, with the following results: 



Moisture .93 per cent 



Sand .00 per cent 



Sodium Sulphate .68 per cent 



Total Arsenious Oxide, As- O3 56.94 per cent 



Cupric Oxide, Cu O 25.56 per cent 



Acetic Acid (by difference) 1589 per cent 



Total 100.00 per cent 



Yours very truly, 

 (Signed) CHARLES W. DREW. 



r " 



As with many other analyses the above shows a deficit in 

 copper and does not show the presence of soltible arsenic. 



In the meantime our Station Chemist had carefully re- 

 viewed the work on sample 7 and made us the following state- 

 ment : 



Agricultural Experiment Station, 



St. Anthony Park. Minn., July 2, 1903. 

 Prof. F. L. Washburn, 



Minn. Agr. Experiment Station, 

 St. Anthony Park, Minn. 



Dear Sir; The conclusion reached in regard to sample No. 7 and 

 formerly reported, namely, that it is not pure Paris Green, I find correct. 



In pure Paris Green there is a definite relationship between the con- 

 tent of arsenious acid and copper oxide. High grade Paris Green should 

 contain from 57 to 59 per cent arsenious acid, and from 29 to 31 per cent 

 of copper oxide. In Bulletin No. 68. Chemical Division. U. S. Depart- 

 ment of Agriculture, analyses of Paris Green samples procured on the 

 open market are given. The smallest amount of copper oxide found in 

 any sample reported was 27.58 per cent, and that was in a sample that 

 contained an excess of free arsenious acid. 



Sample No. 7 contained 22.04 per cent copper oxide, which is at least 

 7 per cent less than is found in high grade goods. This sample contained 

 58.3 per cent of arsenic in the form of Paris Green and in other forms. 

 If the sample were pure there should be 29 per cent, at least, of copper 

 oxide to combine with 58.3 per cent of arsenious acid. A deficit of 7 per 

 cent of copper oxide means that at least 14 per cent of arsenious acid is 

 not in combination with copper, as it should be in pure Paris Green. 

 The microscopic examination shows the presence of foreign matter, as 

 will be observed from the micro-photographic illustrations. 



