1912.] PUBLIC DOCUMENT — No. 31. 193 



Cold water dissolved a small amount of arsenic, Lolling water 

 very much more. The green appisared to resist hot water for a 

 considerable time after which the change was noticeabk^. If 

 the boiling had been continued all the arsenic would i)robably 

 have passed into solution. The .10 per cent, ammonium salts, 

 exclusive of nitrite, dissolved on the average 58 per cent.^ more 

 arsenic than the corresponding sodium salts. In both instances 

 the carbonate was the most active, followed respectively by the 

 sulfate, chloride and nitrate. Sodium bicarbonate was ap])ar- 

 ently inactive under the conditions employed. Free carbonic 

 acid was eifective and so was ammonia when in sufficient 

 amount to overcome the resistance of the green, and jointly, 

 carbonic acid and ammonia dissolved the most arsenic. 



It is evident from what has been stated that carbonic acid 

 and ammonia of the atmosphere in conjunction with dew, fogs 

 or light rains and high temperature will materially increase the 

 dissociation of Paris green. Data more or less contradictory 

 have been offered by various investigators relative to the influ- 

 ence of weather conditions on the effect of arsenic on foliage. 

 While more or less problematical, certain deductions seem war- 

 ranted : conditions favoring a rapid drying of the green and 

 its continuance in a dry state are propitious. For instance, a 

 relatively high temperature, low humidity and a good circula- 

 tion of air at the time of application, followed by warm, dry 

 weather should tend toward a minimum of arsenical injury. On 

 the other hand, factors conducive to solubility of the arsenic 

 and its passage by osmosis into the substance of the leaf are 

 detrimental ; as, for example, warm, " muggy " weather or warm 

 weather accompanied by fogs or heavy dews. Rains are not 

 necessarily injurious if of sufficient quantity to remove the solu- 

 ble arsenic from its sphere of influence. The addition of milk 

 of lime to Paris green tends to reduce arsenical injury by form- 

 ing, with the free arsenic, arsenite of lime insoluble in the 

 presence of excess lime. As lime flocculates the particles of 

 green, it is not advisable to prepare the spray mixture until 

 shortly before application. 



In conclusion, it may be said that Paris green contains a 

 fairly high per cent, of arsenic, is nominally insoluble in water 



' Direct comparison. 



