OF ARTS AND SCIENCES. 



45 



Before the above described method was worked out, it was thousrht 

 that it would give merely an approximation of the amount of arsenic 

 in wall papers and fabrics, which would allow one, for instance, to pass 

 judgment on the articles from a sanitary standpoint. Not only, as 

 will be seen from the table, does the method give an approximation to 

 the actual amount when ordinarily conducted, but with care it can 

 be made to give results worthy of comparison with other quantita- 

 tive methods. The greatest error occurs naturally in the estimation 

 of large amounts, but in this case an approximation would answer 

 until a more exact determination was called for. 



The process will, I think, be also found of great value in toxico- 

 logical work, not only as a rapid means of determining the quantity 

 of ar.senic present, and as a check on other methods, but also as the 

 only means of accurately determining the amount when the arsenic is 

 present in minute quantity. In such work the organic matter would 

 not generally be charred, but the arsenic would be extracted by the 

 method of distillation. I hope to investigate the extension of the 

 metliod to toxicological work. 



The limit of arsenic that I have been able to detect with certainty by 

 the Berzelius-Marsh method is 001 mgr. As.jOg or 0.0007 mgr. As. 

 I shall not here take up the much discussed question of the delicacy 

 of this as compared with other methods, but I think it will be agreed 

 that no other method enables one to determine quantitatively such 

 small amounts. 



In conclusion, I have to thank my assistant, Mr. Charles Walker, 

 very sincerely for his valuable services in most of the analytical work 

 of this paper. 



United States Naval Academy, Annapolis, Md., 

 February, 1891. 



