42 PROCEEDINGS OP THE AMERICAN ACADEMY 



that no arseniuretted hydrogen shall escape decomposition. In this 

 method, the amount of heating surface need not be greater than that 

 given by a good burner, and I have assured myself by direct experi- 

 ment tliat no arsenic escapes under the ordinary conditions vk^hen the 

 size of the mirror is not above O.OG mgr. It is necessary, however, 

 for the stream of gas to be slow and regular. Hence the disadvantage 

 of organic matter in the extract, causing an increased and irregular 

 flow of gas. 



6. The following table contains some analyses, taken at random, 

 illustrative of the method. 



7. Comparison of Results obtained hy the Berzelius- Marsh Process 

 with those obtained by other Methods of Analysis. — In order to test 

 the availability of the process, it became necessary to analyze, by 

 one of the general quantitative methods, some of the papers whicli 

 had been analyzed by the Berzelius-Marsh method. In the analyses 

 given below, the eventual determination was made by an approxi- 

 mately hundredth normal solution of iodine, and, when necessary, 

 titrating back with a sodic thiosulphate solution of corresponding 

 strength. I find a similar method to have been proposed some time 

 ago by Holthof.* Considerable dilliculty was met with at first in 

 finding a suitable method of getting the arsenic from the paper into 

 proper state for titration. A measured piece of paper (100-400 

 sq. cm.) was treated on a porcelain plate with a strong solution of 



• Fresen. Zeitschr., XXIII. 378. 



