THE LEAD ARSENATES. 5 



that permitted by the Federal law. The time required for tlie powder to 

 settle was 255+ minutes, which places this sample far ahead of either of 

 the pastes in this regard. 



Pure Neutral Lead Arsenate Paste. — This material has been highly 

 recommended as being safer on foliage than the acid lead arsenates, and 

 an investigation of it was therefore also made. To obtain it in a pure or 

 nearly pure form was very difficult, however, * and the best sample ob- 

 tainable analvzed as follows : — 



Water, H2O 



Water in combination (calculated) 



Lead oxide, PbO .... 



Arsenic pentoxide, AS2O5 . 



Acetic anhydride, CiHsOs . 



Sodium oxide (calculated to combine with last) 



Carbonic acid, CO2 .... 



Insoluble matter .... 



Per Cent. 



70.97 



.08 



2L10 



7.33 



.10 



.06 



.15 



.01 



99.80 



The original composition of this sample was therefore substantially as 

 follows : — 



Per Cent. 



Water, H2O 70.97 



Water occluded ........— 



Acid lead arsenate, PbHAs04 3.14 



Neutral lead arsenate, Pb3(As04)2 24.61 



Lead carbonate, PbCOs . . . . . . . .91 



Sodium acetate, NaC2H302 . . . . . . .16 



Insoluble matter ......... 01 



99.80 



This sample contained a very large amount (71 per cent) of water, was 

 nearly one-quarter neutral lead arsenate, and contained a little over 3 per 

 cent of acid lead arsenate and rather more than 1 per cent of impurities of 

 such a nature as to indicate that it had not been sufficiently washed to re- 

 move all the acetic acid, and that impure sodium arsenate containing some 

 carbonate had been used from which to obtain the arsenic. None of 

 these materials was apparently present in sufficient amount to cause any 

 foliage injury, — a view sustained by the results later. 



The solubility of the sample in water was .07 per cent on standing 

 twenty-four hours, and it required an hour for complete settling. 



None of the materials showed on analysis the presence of impurities of 

 such kinds and in such amounts as to make injur}' to the foliage from this 

 cause at all probable. 



As a commercial neutral lead arsenate could not be obtained which did 

 not contain a large amount of the acid arsenate also, tests of such a ma- 

 terial were not made. 



I See Holland and Reed, loc. cit., p. 203. 



