6 PARFS GREEN SPRAYING EXPERIMENTS. 



stituents. This is "free" arsenious oxid and until recently it has been 

 considered the only cause of a scorching of the foliage by Paris Green. 



(2) The greens may be poorly made so that the constituents are very 

 loosely held together. When such greens are brought in contact with 

 water, especialty water containing carbon dioxid, they are soon broken 

 up and arsenious oxid is set free. Even the best greens break up to 

 some extent under such conditions, but the poorly made greens decom- 

 pose much more rapidly. Note, then, the effect of such greens upon 

 the foliage. First, the water of the spray would act at once on the 

 green and set arsenious oxid free, then carbon dioxid would dissolve 

 in the water and carry the decomposition of the green still further. 

 But the matter would not end here, for the rain and dew both contain- 

 ing carbon dioxid would also act upon the green and enough free 

 arsenious oxid would soon collect to severely scorch the foliage. This 

 would of course take place more slowly with even the best greens, but 

 unless the climatic conditions were very adverse, not enough free 

 arsenious oxid would be apt to accumulate at one time to cause any 

 serious damage. 



(3) The green may be extremely fine. It is well known that even 

 the best greens when ground to a very fine powder and applied to the 

 foliage will scorch. This is doubtless due to the fact that more sur- 

 face is exposed to the action of water, which may contain carbon 

 dioxid, so that its decomposing action on the green is accelerated and 

 enough free arsenious oxid soon gathers to cause serious damage. 

 Avery and Beans a found that the very best Paris Greens obtainable 

 were slowly attacked by water, and by grinding the same greens to a 

 very fine powder and suspending them in water the rate of decomposi- 

 tion was enormously increased. They also found that carbon dioxid 

 in the water increases the rapidity of decomposition. 



It is a very common occurrence to secure a commercial Paris Green 

 that scalds because of one of the first two causes i. e., either by rea- 

 son of the presence of free arsenious oxid or because it is poorly 

 manufactured but the writer has never found a commercial sample of 

 green that scorched because it was in too fine a condition. In exper- 

 imenting on the third method of scorching even the finest samples of 

 green found on the market had to be ground further before they 

 would scorch by reason of minute division. 



It is thus seen that the chemist will be called upon to examine 

 samples of green (1) for actual free arsenious oxid; (2) for arsenious 

 oxid that may be easily set free on account of the instability of the 

 compound. Methods of determining these two forms of soluble arse- 

 nious oxid have been devised during the last few years which, though 

 not strictly accurate, will give results close enough for all practical 



J. Amer. Chem. Soc., 23: 111. 



