June, '10] REVIEWS 323 



As a consequence, spraying with some brands might prove inefficient, simply 

 because of the small amount of poison present, or might cause injury to 

 the foliage because of an excessive amount of soluble arsenic. It is notice- 

 able that there is a great difference in the amounts of arsenic and lead 

 j>resent in the different samples analyzed. This should make a great differ- 

 eiu-e in the preparation of the material for application to the trees. In one 

 case noteil, the material which is evidently in the form of a dry powder, 

 contains more than twice as much arsenic as in another sample which is in 

 the form of a paste and contains over sixty per cent, of water. To prepare, 

 such widely differing samples by the same fornnila for spraying would he 

 liable to lead to most divergent results. 



The second section of the bulletin treats of "home-made" lead arsenate 

 and the chemicals entering into its manufacture. Analyses of samples of 

 lead acetate, lead nitrate and sodium arsenate gave, for the most part, quite 

 satisfactory results, the latter showing the greatest variations in composition. 

 Attention is called to the point that when sodium arsenate having an unusually 

 high per cent of arsenic is used, it is possible that ordinary formulas would 

 fiiil to provide lead enough to combine with all of this, thus leaving a soluble 

 salt of arsenic in excess in the spray to endanger the foliage. 



Comparison of numerous published fornuilas shows considerable variation 

 in the amounts of the different substances to be taken, leading in some cases 

 at least, to the addition of materials which will be in excess of the amounts 

 needed. To avoid this, directions for preparing lead arsenate both with lead 

 acetate and with lead nitrate are given, for the different usual grades of 

 sodium arsenate. It is not probable, however, that the average sprayer will 

 take the trouble to test the material to determine when the lead comes to be 

 present in excess, much as this is to be desired. 



I'ntil the present time, the general {ireference seems to have been in favor 

 of using lead acetate instead of lead nitrate as a material. Comparative 

 experiments here given, seem to favor the latter as being slightly cheaper, 

 slightly more poisonous and the lead arsenate produced by its use settling 

 nmch more slowly than that made from the acetate. This would seem 

 to differ from the results obtained by Colby, who found (if the recollection 

 of the reviewer be correct) that the arsenate of lead made from lead nitrate 

 settled much more quickly than that made from the acetate, and it would now 

 seem desirable to repeat these tests. An added point not mentioned in this 

 bulletin is that after standing a while, the acetate becomes delequesceut, 

 thus changing its value. 



The third, and in some regards the most interesting' section of the bulletin 

 is devoted to the action of lead arsenate on foliage, the results of investiga- 

 tions in which Mr. A. L. Quaintaince of the Bureau of Entomology, co- 

 operated with the authors. Starting from quoted statements of the safety of 

 the material at almost any strength, the fact that injury results in some 

 cases despite tliese views, led to inquiries as to the cause, atmospheric 

 conditions as the explanation seeming to be the most probable. These were 

 studied for six months in 1907 and 1908 in connec^tion with the spraying. 

 The conclusions reached are, of course, tentative, but so far as they go, 

 indicate that more or less decomposition of the lead arsenate was causetl 

 by the presence of various salts in the water, particularly sodium chlorid and 

 perhaps sodium carbonate. Weather conditions also appeared to have some 

 effect, injury results to the foliage (and fruit) following an application 



