35 



of the trees last sprayed September 3, apples were picked on the 

 lOth of that month and brought to the office in a sack. From 

 these, sound examples were taken at random and submitted to 

 Prof. William McMurtrie, of the chemical laboratory of the Uni- 

 versity, for analysis. According to his report* these apples aver- 

 aged .9 milligram of arsenic each, — an amount such that seventy- 

 four apples would convey a poisonous dose. 



During the interval between the last spraying and the harvesting 

 of these apples, a violent storm had occurred, an inch or more of 

 rain falling, and the wind blowing a gale for two days. 



These facts clearly indicate that exposure to a week's ordinary 

 weather, with heavy rain and wind, is not sufficient to free the ap-. 

 pie from a dangerous amount of Paris green. 



Eemembering that arsenic is one of those substances likely to have 

 a cumulative effect if taken long in small quantities, remaining in 

 the system and finally producing powerful results from very small 

 doses, it will be seen that it would not do to have the family ap- 

 ple supply dusted, even very lightly, with any arsenical substance. 

 I only mention these matters to indicate the great importance of 

 a careful investigation as to the length of time and the circum- 

 stances within which Paris green may be safely used in the or- 

 chard. Certainly we may say that it would be quite inexcusal)le to 

 apply it during the latter part of the season, or, indeed, for some 

 time previous to the ripening of the apples, whether they are early 

 or late. 



As the codling moth continues its attack throughout the entire 

 summer, small larvae appearing in our collections as late as Sep- 

 tember, it is clear that Paris green, even if completely effective- 

 when thoroughly applied, cannot be relied upon wholly to prevent 

 injury by this insect. During the latter part of the season, when 

 its use is inadmissible, the apples will be subject to damage by 

 the later codling moths. 



LONDON PURPLE. 



The London purple experiment was in all respects similar to that 

 with Paris green, except that a somewhat smaller ratio of the 

 poison was used and that only one tree was carried through the 



*Univeksity of Illinois, Depaetmfnt of Chemistkt, I 

 Champaign, 111., October 20, 1885. f 

 P)-of. S. A. Forbes, State Entomologiai: 



Dear Sib: I have the honor to submit the following report upon examination for ar- 

 senic upon apples from trees which had received arsenical spray for destruction of In- 

 sects. 



The apples were preserved, as received, in a closed box until needed for examination. 

 First one was taken and submitted to qualitive test for arsenic by the application of the 

 Marsh test. The presence of the poison was detected. To determine the quantity of ar- 

 senic present another and large apple was selected, treated t<j destroy its organic constit- 

 uents, and the arsenic separated in the metallic state by means of the Marsh apparatus as 

 before. The results are as follows: 



Weight of apple taken. 76.025 grammes; weight of arsenic secured, 0.0009 grammes; 

 percentage of arsenic, 0.0013. 



Kespectfully submitted. 



WM. McMURTRIE, E. M. Ph. D.. 



Prof, of Chemistry, University of Illinois. 



