36 



in 58 grams of leaves). Two analyses of leaves injured by Paris 

 green in the same lot showed no arsenic in the texture of the 

 leaf. The poison in the latter case had acted from the surface of 

 the leaf. It is apparent that London purple is the more injurious 

 because of its soluble arsenic. The arsenic in London purple is 

 in the form of a normal arsenite of calcium, which substance com- 

 prises about 72 per cent, of the whole compound, and over 50 

 per cent, of it, or ?iearly 4.0 per ce7it. of the London purple, is 

 quickly soluble in water. Paris green contains no soluble arsenic* 



Trials were now made to determine just what portion of the 

 London purple compound is harmful to foliage. 



11. Peach foliage was sprayed July nth with the filtered solu- 

 ble portion of London purple. The foliage showed marked signs 

 of injury in three days, and a week later the leaves had fallen and 

 the shoots were much damaged. This proves that it is the solu- 

 ble portion which is hurtful. 



* Those who wish to make a more careful study ot" the composition of 

 London purple and Paris green are referred to the following determinations 

 by Harry Snyder, Asst. Station Chemist : 



London Purple is a refuse from a dye manufactory, and contains, in ad- 

 dition to the dye that is present, arsenic in both the soluble and insoluble 

 forms ; and the reactions all indicate that it is in the form of an arsenious 

 compound, and none present in the form of an arsenic. Other substances 

 found to be present are iron, aluminum, and sulphuric anhydride ; these, 

 however, were found only in small quantities, which leaves the calcium and 

 arsenic to combine as a calcium arsenite. 



There are three arsenites of calcium, corresponding to the formulae : 



1. Ca 3 (AsO s ) 2 ; which contains 30.50 per ct. Ca 40.98 per ct. As. 



2. Ca (AsOJ 2 " " 15.75 •« " 59.04 " 



3. Ca 2 (As 2 O s ) " " 25.80 " " 48.39 " 



The first (Ca 3 (As0 3 ) 2 ) is the normal calcium arsenite. 



The Loudon purple yielded on analysis, (average of duplicate results) cal- 

 cium and arsenic in the proportion of 11. 19 per cent, calcium and 14.88 per 

 cent, arsenic ; this corresponds to the amount of calcium and arsenic in 

 the normal calcium arsenite, for 



Ca As Ca As 



30.50 : 40.98 : : x : 14.88, 



which gives 11.08 per cent, of calcium against 11. 19 as found. 



Analyses of London purple : 



I. II. Average. 



Ca 3 (As0 3 ) 2 72.62 per ct. 72.46 per ct. 72.54 per ct. 



Fe 2 3 and A1 2 3 1.01 1.05 1.03 " 



S0 3 .44 .40 .42 " 



Moisture, 3.03 2.91 2.97 



Dye (by difference) 23.04 



The water solution, after being filtered, yielded on analysis an amount of 

 arsenic and calcium in proportion of 9.80 per ct. arsenic and 6.56 per ct. of 

 calcium ; these amounts also satisfy the formula, Ca 3 (As0 3 ) 3 , showing that 



