retained in the process or manufacture. No doubt this is a valuable aid, 

 still the actual amount present cannot be determined in this way. The 

 only way to decide whether this substance is present in injurious quan- 

 tities or not is by an actual estimation through the means of chemical 

 analysis. 



Precautions in the Use of Paris Green. Since the last method of 

 estimating- the free arsenious oxide of Paris green is not within the ready 

 reach of all, it is well to assume that it is present in harmful quantities 

 and to use something to alleviate the difficulty, if such there be. As before 

 stated, arsenious oxide, 01 "white arsenic," may be combined with other 

 substances which will neutralize or destroy its acid or burning property. 

 Lime is one of these substances. // an equal quantity of good, freshly 

 slaked lime he added to the Paris green, in suspension in the water, some 

 little time before spraying, it will combine with the free arsenious oxide 

 and overcome its leaf=scorching power to a great extent. It is well also 

 to know that some kinds of foliage are much more susceptible to the de- 

 stroying power of arsenious acid than others ; thus the peach tree has 

 foliage which is remarkably tender, whereas the foliage of the apple is 

 very hardy. 



From investigations carried on in 1902-3, the results of which are 

 embodied in Bulletin 82 of the Bureau of Chemistry,' Washington, D.C., 

 J. K. Haywood was enabled to make out a schedule showing the amount 

 of free arsenious oxide which the foliage of the more common fruit trees 

 will withstand. His results, -which also^ give figures showing the influence 

 which lime exerts, and are thus doubly valuable, are summarized in the 

 following table : 



Average Percentages of Soluble Arsenious Acid Allowable. 



This shows plainly that the orchardist must consider the kind of 

 foliage he is spraying as carefully as the kind of Paris green he is using. 



Total Arsenious Oxide in Paris Green. Since Paris green owes its 

 insecticidal value to the arsenic which it contains, it follows that the 

 larger the proportion of arsenious oxide there is present in it, the more 

 effective it will be when used against insects. The value of any arsenical 

 is determined by its arsenic content. Pure Paris green contains 58.65 

 per cent. As-^0 3 -. Any quantity above that must be present in the free 

 state, and any quantity below that lowers the insecticidal, and, thus, the 

 market value, just to the extent to which it is deficient. The commercial 



