OP ARTS AND SCIENCES. 25 



were necessary for its adoption as a trustworthy analytical method. 

 Their process has found its way into the text-books, and needs no ex- 

 planation here. I note its use by Hubbard* in 1882, and Prescottf 

 in 1886, and undoubtedly many others have employed it in toxicologi- 

 cal work. It seems remarkable, therefore, that the previous applica- 

 tion of the process to quantitative work should have escaped the 

 attention of Kiihn and Saeger,J as well as Polenske,§ to whom they 

 refer as the first to propose the method. Kiihn and Saeger's article, 

 published a few months ago, contains nothing new ; but as the paper 

 of Folenske is inaccessible to me, I cannot say what modification he 

 may have introduced. 



I need not refer here to the numerous quantitative methods which 

 depend on the reduction by nascent hydrogen and absorption of the 

 arseniuretted hydrogen by argentic nitrate, the eventual determina- 

 tion of the arsenic being made from the silver solution in a variety of 

 ways. These methods form a class by themselves, and cannot be in- 

 cluded in the Berzelius-Marsh process. 



All methods for the estimation of arsenic are open to a common 

 objection ; they do not allow the estimation of minimal, or even, with 

 accuracy, of small amounts. It happens so often that a small amount 

 of arsenic must remain unestimated, because unweighable, and only 

 an approximation to the real quantity can be made. 



In the qualitative analysis of wall papers and fabrics by the Ber- 

 zelius-Marsh method, much confusion results from the careless man- 

 ner of reporting the amount of arsenic which makes its appearance in 

 the reduction tube. The reports, " trace," " small amount," "large 

 amount," are usually made without reference to any standard mirrors, 

 time of heating the reduction tube, or, in many cases, to the amount 

 of substance taken for analysis. On account of the want of a definite 

 quantitative method which could be easily applied to wall papers and 

 fabrics, there have been some propositions for a rough quantitative 

 determination, which should serve as a control as to whether the 

 substance contained more or less than a prescribed amount. The 

 Swedish law || of 1883, for instance, though not using the Berzelius- 



— * - 



* Pliysician and Surgeon, Ann Arbor, IV. 348 ; also, Contributions from the 

 Chem. Lab. Univ. Mich., Vol. I. Part I. p. 12. 

 t Chera. News, LIII. 79. 

 t Ber. d. deutsch. chem. Gesell., XXIII. 1798. 

 § Arb. a. d. kais. Gesundheitsamt, Bd. V. Heft 2 (1889). 



II Correspondence between the English and other Governments respecting 

 the Presence of Arsenic ... in Wall Papers and Textile Fabrics. Com" 

 mercial, No. 40 (1883). 



