TWENTY-FIRST ANNUAL MEETING. 211 



finally heated to boiling. It is then allowed to cool and 

 settle, and the clear solution decanted through a filter. 

 The ammonia is then dri\en out of the filtrate by boiling, 

 and the remaining solution made distinctly acid with acet- 

 ic acid, after which a concentrated solution of lead acetate 

 with free acetic acid is added. 



If a considerable precipitate forms at this stage of the 

 test, it is evident that the original sample contained con- 

 siderable quantities of arsenic in other forms than the neu- 

 tral ortho-arsenate and hence would probably prove inju- 

 rious if applied to foliage in combination with lime-sulphur 

 solutions. If no precipitate forms at first, there may possi- 

 blv still be some objectionable arsenates present. Their 

 presence may be determined by adding the lead acetate solu- 

 tion in large excess and allow to stand, whereupon a pre- 

 cipitate may form in a few minutes or an hour. If no 

 precipitate forms under any of these conditions, the origin- 

 al sample contained nothing but true neutral ortho-arsen- 

 ate of lead. 



Dr. Stewart gave an interesting and important paper, 

 illustrating his subject with a large number of lantern slides. 

 The cause of spray injury and its possible elimination has 

 never been more forcibly brought out. 



Discussion. 



Dr. Brittox : This has been a very interesting lecture, 

 and I only wish that we in Connecticut knew as much 

 about the chemistry of these spray mixtures as does Pro- 

 fessor Stewart. We have not gone deeply into it. 



One point has been brought out here this morning 

 that I am afraid may be a trifle misleading. Professor 

 Stewart's figures show^ us the eflfect obtained from the use 

 of arsenate of lead with various mixtures, including Pyrox 

 and Bordeaux, and he stated that the injury was due to 

 the arsenate of lead. Now, some may get the idea that 

 it was due to the arsenate of lead alone, notwithstanding 



