44 



PROCEEDINGS OP THE AMERICAN ACADEMY 



ence of volatile organic matter not destroyed by the potassic chlorate, 

 the addition of a few drops of strong nitric acid and evaporation ex- 

 pelled the organic matter. The residue was then vpashed into a flask 

 with about 50 c. c. water, and reduced and titrated as in the previous 

 cases. 



The method was tested by the following analyses of filter paper to 

 which known amounts of arsenic were added, 200 sq. cm. of paper 

 beinw used in each case. 



The residues from the distillations in the last analyses were, after 

 the addition of a few drops of nitric acid, charred with sulphuric acid 

 and " marshed," giving mirrors corresponding to 0.015 mgr. and 0.02 

 mgr. respectively, showing that a mere trace was left in the flasks. 



The following papers were analyzed by this method. 



Number of 

 Paper. 



194 . 



194 . 



406 . 



406 . 



39 . 



39 . 



892 . 



393 . 



393 . 



359 . 



359 . 



Sq. Cm. C.c. Iodine u.sed. 



taken. 1 c.c. =0.!)815 Mgr.ASjO,. 



. 200 17.20 



. 200 17.30 



. 400 3.10 



. 400 3.00 



. 400 2.80 



. 400 270 



. 380 1.80 



. 400 0.38 



. 400 0.36 



. 400 130 



. 400 1.10 



Mgr. A.'SjOj found 

 per Sq. Meter. 



844.00 

 849.00 



76.07 



73.61 



68.71 



66.25 



46.50 

 9.33 

 8.83 



31.90 



27.00 



Finally, the following table shows the comparison of the results 

 obtained by the volumetric method with those obtained on the same 

 papers by the Berzelius-Marsh method. The first two columns com- 

 pare the results in milligrams per square meter, and the second two 

 in grains per square yard. Each result is the mean of two, unless 

 specified. 



