36 PROCEEDINGS OP THE AMERICAN ACADEMY 



1 c. c. contained 0.01 mgr. AsgOs, as AsoOs- The mirrors agreed 

 sharply. This is at variance with the results of Headden and Sadler,* 

 who found, in using the method of Chittenden and Donaldson, that 

 it was necessary to subject the arsenic acid to preliminary reduction 

 in order to obtain all the arsenic present. The reason for this is, 

 probably, that a vei'y small quantity of arsenic acid, such as would 

 occur under the conditions of this method, is more quickly reduced 

 by nascent hydrogen, while the comparatively large quantity used by 

 Headden aud Sadler would take more time. They do not show that 

 prolonged treatment in the Marsh reduction flask would not have 

 eliminated this error. 



e. The Use of Nitric Acid as an Oxidizer. — Nitric acid suggests 

 itself at once as the most convenient oxidizing agent. In this con- 

 nection may be mentioned the method proposed by Blyth,| which 

 consists in soaking the paper in potassic chlorate, drying, burning, and 

 extracting with water. Hager % substitutes sodic nitrate for the po- 

 tassic chlorate. Many destroy the organic matter by hydrochloric acid 

 and potassic chlorate, as in the case of tissues. Lyttkeus § uses sul- 

 phuric acid and potassic chlorate, and Lenz,]| commenting on this, con- 

 siders it the best means of treatment of the paper. The German 

 law IT of 1888 prescribes the treatment of fabrics with strong hy- 

 drochloric acid aud distillation with ferrous chloride. None of these 

 methods in the analysis of wall papers and fabrics have any advantage 

 over charring with the simple addition of nitric acid, and all require 

 more time. 



That all the arsenic may be recovered when nitric acid is used is 

 shown by the following: 0.01 mgr. arsenious oxide was added to 100 

 sq. cm. of filter paper and a drop of strong nitric acid added before 

 charring. The mirror obtained corresponded to 0.01 mgr. 



1 mgr. AS2O3 and 5 cc. sodic chloride solution (5 mgr. chlorine) 

 were added to 100 sq. cm. filter paper and treated with a mixture of 

 one part nitric to six parts sulphuric acid. Duplicate readings gave 

 1.095 mgr recovered, an error no greater than that wliich might 

 occur from the method. 



10 mgr. As203,as AS2O5, were added to 100 sq. cm. filter paper, and 



* Amor. Cliem. Journal, VII. 338; Ber. d. deutsch. Chem. Gesell, XIX. 116. 



t Loc. cit , p. 632. 



I Pliarm. Centrallialle, XIII. 145. 



§ Ref. Frcs. Zeitsclir., XXII. 147, from Landw. Versuchsstat., XXVI. 305. 



lIFres. Zeitsohr.. XXII. 147. 



If Ibid., XXVII. 471. 



