﻿130 H. Carmichael — Determination of Arsenic. 



estimation of small quantities of arsenic, quicker, simpler, 

 easier, more delicate, and, in the hands of toxicologists, less 

 exposed to fallacy than any other. 



A smooth, polished sheet of pure copper, not thicker than 

 0'05 mm , is selected. As the commercial article is usually var- 

 nished, it must be cleaned with alcohol or otherwise. A neg- 

 lect of this precaution is indicated by the irregularity of the 

 arsenical deposit. The copper is cut into pieces 20x21 mm . 

 A strip one mm. wide is cut nearly across the longer side of 

 each, and bent at a right angle to the general surface. These 

 are the normal squares, and the bent strips are the handles by 

 which they are manipulated. In applying the method, if the 

 arsenic is possibly present in the substance under examination 

 as an arsenic compound, it is digested with strong sulphuric 

 acid, the solution reduced to a small volume, and after the con- 

 version of the arsenic into arsenious oxide, strong chlorhydric 

 acid is added. If the substance can only contain arsenic in the 

 arsenious form, it is reduced to a small volume if liquid and 

 strongly acidulated with HC1. 



The acidulated solution is brought into a small porcelain 

 capsule and a square of copper introduced. The capsule is 

 placed over a small flame, and the square moved back and forth 

 until it has acquired the tint of the standard chosen. The 

 copper is removed, carefully washed and dried. The strength of 

 acid is maintained by occasional additions, and squares are made 

 to succeed one another until there is no further discoloration. 

 The last square is usually lighter than the normal. Multiply 

 the number of squares by the volume of standard arsenious 

 solution which is necessary in coloring equally a single square, 

 and subtract an amount which it is shown by trial the last 

 square has required less than a normal square, and the total 

 amount is given. By altering the concentration, the acidity, or 

 the temperature, the rate of deposition is readily controlled. 

 Two examples will illustrate the method. 



(a.) A square of wall paper two inches on a side was placed 

 in a capsule and drenched with strong HC1. A small flame 

 was brought under capsule and squares of copper were succes- 

 sively colored to the standard until the exhaustion of the 

 arsenic was marked by the lighter color of a surface long 

 exposed to -the acid liquid. The last was matched by a square 

 which was known to have withdrawn 0'l3 mgrm and the other 

 five by a square which had withdrawn 0'23 mgrm . The total 

 amount, therefore, to the square }^ard of paper was 4l4-7 m s rm . 

 of arsenious oxide. The analysis, which consumed but a few 

 minutes, was qualitative as well as quantitative. It may be of 

 interest to state that the paper was " warranted strictly free 

 from arsenic." 





