Medico-Legal Application of Riench 's Test for Arsenic. 245 



mortar of sufficient hardness. The particles of glass cannot in- 

 terfere with any test to be used.* A portion of the powder thus 

 obtained should be digested in pure water, and tested by ammo- 

 nia-nitrate of silver, sulphuretted hydrogen, &c. Another part 

 may be reduced with charcoal, and a third portion introduced 

 into Marsh's apparatus. 



In examining the delicacy of the foregoing process, it was found 

 that one part of metallic arsenic in 200.000 parts of fluid can 

 be detected, and T ij gr. sublimed and satisfactorily recognized. 

 Mr. Brett (Lond. Ed. and Dub. Phil. Mag., No. 132) did not suc- 

 ceed in detecting less than 00469, or nearly ^j^ gr. of metal, by 

 Marsh's apparatus. M. Riench considers the discoloration of the 

 copper as a sufficiently delicate test for arsenic, but in my re- 

 searches the color of the deposit did not appear so perfect a means 

 of discrimination as the production of the sublimate of acid. Its 

 adamantine lustre and triangular facets are much more distinc- 

 tive ; the ease with which it can be volatilized — its rising with- 

 out previously fusing, are all characters rarely met amongst chem- 

 ical substances, and are collectively, common to no other body. 

 The length of time requisite to conduct an analysis up to the 

 production of the sublimate, when the solution does not offer any 

 cause of delay, does not exceed five minutes, for a small quantity. 

 But the presence of other metals in the solution, as well as the 

 impurities of commercial muriatic acid, are sources of embarrass- 

 ment which it is necessary to examine before this test can be re- 

 commended to the profession. This inquiry forms the third di- 

 vision of our subject. 



3. Arsenic exists in many specimens of hydrochloric acid met 

 with in commerce. Such an adulteration is fatal to the delicacy of 

 Riench's test ; and the acid used in the foregoing process must 

 be first carefully examined and purified. The method recom- 

 mended by M. Riench for this purpose is the best — boiling the 

 acid along with bright copper strips, as long as they continue to 

 be stained with arsenic. The quantity of acid used must be in 

 proportion to the amount of fluid; there is no danger of using too 

 much. But the presence of remedial agents in the suspected 

 mixtures is a source of much more difficulty. In the November 



* It should always be remembered that glass not (infrequently contains arsenic, 

 which is used in its manufacture as a deoxidizing and decoloring agent. Every 

 sample of glass to be employed in toxicological experiments, should therefore be 

 carefully examined to prove its purity. — Eds. 



