34 PROCEEDINGS OF THE AMERICAN ACADEMY 



found to be true to an extent sufficient to warrant the precaution of 

 adding a small quantity of nitric acid to the sulphuric acid, iu order 

 to prevent the formation of arsenious chloride. 



a. The Presence of Chlorides in Wall Papers. — In order to deter- 

 mine to what extent chlorides exist in wall papers, several analyses 

 were made of papers taken at random. The method was as follows. 

 A measured amount of paper (400 sq. cm.) was thoroughly mois- 

 tened with a strong solution of potassic nitrate (free from chlorine) 

 on a broad porcelain plate, dried on the plate, and ignited over the 

 plate. The organic matter was practically destroyed. The residue 

 was transferred from the plate to a chlorine free filter, and washed 

 thoroughly with hot water. The filtrate, after acidification with 

 dilute sulphuric acid, was boiled to expel nitrous acid, and, after 

 cooling, titrated according to Volhard with approximately hundredth- 

 normal solutions. There is no danger of volatization of hydrochlo- 

 ric acid even on prolonged boiling, as Gooch and Mar* have 

 shown that a solution containing 0.12 per cent of hydrochloric acid 

 can be boiled down one half without appreciable loss. In titrating, 

 as well as in determining the strength of the standard solutions, it 

 was found that the dilution of the solution affected the end reac- 

 tion in that the color of the ferric sulpho-cyanate was obscured by 

 that of the argentic chloride, even if the latter were made to 

 " clump together." This difficulty was easily obviated by heating to 

 boiling after adding excess of argentic nitrate, filtering off the 

 chloride, and titrating back in the cooled filtrate. The end reaction 

 was then as sharp as possible. 



Analysis of thirteen papers gave an average of 138 milligrams of 

 chlorine per square meter, or 1.38 mgr. in the usual amount (100 

 sq. cm.) taken for the determination of arsenic. The higliest amount 

 was 238 mgr., the lowest 56 mgr. In no case was a paper found 

 free from chlorides. 



h. Effect of Chlorides. — A solution of sodic chloride free frorn ar- 

 senic was made up of such strength that 1 c. c. contained 1 mgr. 

 chlorine. Several trials were made of the effect of a known amount 

 of chloride on small amounts of arsenic. 100 sq. cm. S. and S. filter 

 paper (589) were used in each case. After addition of the arsenic 

 and sodic chloride solutions, the paper was dried in the evaporating 

 dish, and the arsenic determined exactly as described, but without 

 using nitric acid. Tiie following table shows the results obtained. 



* Amer. Jour. Science, [3 ] XXXIX. 2U3. 



