M. Berzelius on the Detection 



ing a partial differential equation, arrived at the same construc- 

 tion as was used on page 337, vol. i., and which represents the 

 relation between the common and true scales of temperature, 

 viz. that when the variations on the latter are uniform, those on 

 the former follow a geometrical progression. 



On the Detection of Arsenic in cases of Poisoning. By J. L. 

 Berzelius. 



XN cases of poisoning with arsenic, the individual may have 

 taken the deadly poison either in the pulverulent form, or in a 

 state of solution. In the first case, we can almost always detect 

 visible particles of arsenic in the contents of the stomach, or on 

 the inner coat of the stomach, where they are distinguished by 

 dark red spots, on which they are to be looked for. The na- 

 ture of these particles, although much under the one-tenth of a 

 grain in weight, may be ascertained with great care and perfect 

 certainty by the process or test of reduction. The following 

 method I employ in the use of this test :—A glass tube, from 

 one-tenth to one-seventh of an inch in diameter, is drawn out, at 

 one extremity, into a fine point, from two to three inches in 

 length, which ought not to be wider internally than the thickness 

 of a coarse knitting needle, and is then hermetically closed at the 

 extremity. 



( i -r ^' ^ -^ 



The particle of arsenic (even the one-hundredth part of a grain 

 in weight is more than is necessary), is moved upwards to a, and 

 covered with charcoal powder, which has been previously exposed 

 to the flame of the blowpipe, to drive ofl* any moisture it might 

 contain, to 6. The tube is then brought, in a horizontal position, 

 into the flame of a spirit of wine lamp ; and in such a way, that a, 

 where the grain of arsenic lies, remains beyond the flame. As 

 soon as the charcoal at h is heated to redness, a is brought into 

 the flame, by which the arsenious acid is converted into gas ; 

 and, during its passage through the glowing charcoal, is reduced. 

 The metallic arsenic is condensed in the small tube, at th'e line 



