THE LEAD ARSENATES. 6 



The impurities present here — the lead cliloride and insoluble matter — 

 occur in such infuiitesimal amounts and are of such a nature that they 

 certainly could not cause any injury on foliage. 



As the purpose of using this material was to test acid lead arsenate, the 

 presence of nearly 5 per cent of the neutral salt was unfortunate; but, as 

 will be sho\\'n in stud^Tlng the results followang the use of the neutral salt, 

 its presence here would, if anything, tend to increase the safety of the 

 spray rather than reduce it. The substance, then, was rather more than 

 half arsenates of lead and rather less than half water. 



This material, mixed with water at the rate of 1 part of the dry matter 

 of the paste to 1,000 of water and kept twenty-four hours, gave .03 per 

 cent of arsenic pentoxide (AsiOr,) as entering into solution during that 

 time. As the Federal law permits .75 per cent of solubility under such 

 conditions, it is e\ddent that the sample was of excellent quality from this 

 standpoint. 



The rate at which lead arsenate settles when mixed with water is also 

 an important factor, those brands which settle most slowly being dis- 

 tributed most evenly over the tree in spraying. This sample had com- 

 pletely settled eighty-one minutes after a thorough mixing, which is 

 excellent for paste lead arsenates. 



Commercial Lead Arsenate Paste. — This material, purchased from a 

 dealer, was of a brand commonly used. Analyzed, it gave: — 



99.85 



The probable original composition of this paste was substantially as 

 follows : — 



Per Cent. 

 Water, H2O . • 46.32 



Water in occlusion . 



Acid lead arsenate, PbHAs04 



Neutral lead arsenate, PbaCAsOj)! 



Iron and aluminum as ferric arsenate 



Lead chloride, PbCh 



Nitric acid, HNO3 . 



Insoluble matter 



.19 



37.96 



13.50 



.54 



1.22 



trace 



.04 



99.77 



In this material less than 2 per cent could be termed impurities, and 

 these were of such a nature as to make it practically certain they could 



