OF ARTS AND SCIENCES. 33 



Appendix. — Analytical and Experimental Work. 



The experimental work in the investigation of the availability of 

 the method is given in detail in the following pages. 



1. Necessity of Charring. — Considerable. difference of opinion ex- 

 ists as tx) the necessity for insuring the absence of organic matter in 

 the extract to be tested. Odling,* in 1859, in testing for arsenic 

 in tissues, found that he could obtain arsenic by Reinsch's test in the 

 presence of organic matter, but not by Marsh's. After getting rid 

 of the organic matter by distillation with hydrochloric acid, he had 

 no difficulty with the Marsh test. Blondlot f calls attention to the 

 necessity of completely destroying the organic matter. Chittenden 

 and Donaldson, t on the other hand, were able, in the presence of or- 

 ganic matter, to detect very small amounts of arsenic, and consider it 

 of no hindrance. My experience has been, that, while the organic 

 matter may not completely prevent the deposition of small amounts, 

 and is no hindrance in the detection of large amounts, yet the char- 

 acter of the mirror is so altered that comparison with the standards is 

 impossible. Besides, the organic matter causes an increased and 

 irregular flow of gas which tends (App., -">./) to carry undecomposed 

 arseniuretted hydrogen out of the tube. I therefore take the precau- 

 tion, by thoi-oughly charring, to insure the absence of organic matter 

 in the extract. 



Thorns § digests 100 sq. cm. of the paper on the water bath with 

 (1-7) sulphuric acid, and adds the filtrate directly to the reduction 

 flask. Fleck || considers that digestion with a 25 per cent sulphuric 

 acid is sufficient to extract the arsenic completely, and ReichardtlT 

 concurs in this opinion. I cannot agree with this, and consider that 

 the chance of the ai'senic being held as arsenious sulphide is alone 

 enough to condemn the method (App., 2. c), not to speak of the 

 organic matter extracted. 



2. Use of an Oxidizing Agent in Charring. — In case the paper con- 

 tains chlorides, it seemed likely that a portion of the arsenic would 

 be volatilized during the treatment with sulphuric acid. This was 



* Guy's Hospital Reports, V. 367-374. 

 t Loc. cit. X Loc. cit. § Loc. cit. 



II Rep. analyt. Chem., 1883, Heft 2. 

 1 Archiv d. Pharm., CCXXI. 271. 



VOL. XXVI. (n. 8. XVIIl.) 3 



