OP ARTS AND SCIENCES. 



35 



Analyses 1-6 were made with duplicate readings which agreed 

 closely. 



Analyses 1 and 2 show that the presence of twice the theory of 

 chlorine causes a large loss, with an amount of arsenic comparatively 

 large. Analysis 3 shows a marked loss with less than the theory. 

 Analyses 4 to 7 were made with more chlorine than the average found 

 (1.38 mgr.), but less than the greatest amount (2 38 mgr.); the 

 amounts are respectively 4, 20, 40, and 200 times the theory, and the 

 conditions are more nearly those met with in practice than in analyses 

 1 to 3. It will readily be seen that the loss is sufficient to warrant the 

 precaution of using an oxidizing agent. 



c. Loss by Retention of Arsenic in the Char as Arsenioiis Sulphide. 

 — The presence of the sulphide in papers is not very common. Yet 

 papers colored with ultramarine occur frequently, and the sulphu- 

 retted hydrogen set free from this by the sulphuric acid acts on the 

 arsenic compound, and thus a large part of the arsenic remains in the 

 char as the sulphide, insoluble in dilute sulphuric acid. The follow- 

 ing analyses of a paper are sufficient to show the danger of loss from 

 this .source. The paper had a light blue ground, and the odor of 

 sulphuretted hydrogen was apparent on addition of sulphuric acid. 

 100 sq. cm. charred with sulphuric acid and a few drops of nitric acid 

 gave aa amount of arsenic corresponding to 5.9 mgr. per square 

 meter. 100 sq. cm. charred with sulphuric acid alone gave 4.5 mgr. 

 per square meter. The char was then extracted with ammonia, and 

 the extract evaporated with sulphuric acid and a drop of nitric acid. 

 This yielded 0.01 mgr., corresponding to 1 mgr. per square meter 

 and bringing the total amount up to 5.5 mgr., which agrees with the 

 first analysis. 



d. The Deposition of Arsenic from a Solution of Arsenic Acid. — 

 The question arises whether the conversion of the arsenious to arsenic 

 acid by use of an oxidizing agent would cause the arsenic to be held 

 back. This was quickly determined by comparison of the standard 

 mirrors with a set prepared from a solution of arsenic acid, of which 



