Dr. Andrew Fyfe on the Detection of Arsenic. 48 



cordingly tried, and with all the rest was found to be equally 

 delicate. The following are a few of the results : — 



1st. AsO^-j-SO^ HO + Water were boiled together for some 

 time, and ClNa was then thrown in and distillation carried on. 

 SH passed through the product of distillation, gave a copious 

 yellow deposit, and NO^ AgO + filtration + rod dipt in NH^, gave 

 a yellow precipitate. 



2nd. Strong solution of starch was treated in the same way ; 

 SH and the addition of NO^ AgO + NH^ gave the same results. 



3rd. AsO^ was boiled in a solution of starch and gelatine, 

 and the product of distillation was collected in the usual way ; 

 when treated with SH and NO^AgO + NH^, it gave no indica- 

 tions of the presence of arsenic. 



4th. Trials similar to 1 and 2 were made with barley broth 

 and hare soup, with the same results. 



5th. To try the delicacy of the test, 0*5 -0-1 -0*05 gr. of 

 AsO^ were boiled, each in an ounce of hare soup, with SO^ HO, 

 to which was afterwards added CI Na. In the product of distil- 

 lation arsenic was detected by SH. In the last trial the AsO^ 

 was dissolved in nearly 10000 of fluid. 



6th. A quarter of an ounce of flesh was soaked for 24 hours 

 in a solution consisting of 0'5 gr. of AsO^ in one ounce of 

 water. The flesh was then boiled for some time in SO^, slightly 

 diluted and distilled with ClNa. In the distilled liquor arsenic 

 was easily detected by SH. 



The only metal likely to cause a source of fallacy in this 

 method of detecting the presence of arsenic is antimony, which, 

 with chlorine, forms a volatile chloride. But the antimonial 

 compound which may be supposed to exist in a suspected fluid, 

 I mean tartar-emetic, does not yield a volatile compound when 

 treated with oil of vitriol and sea-salt, or, if it does, does so with 

 great difficulty. Allowing that it does afl'ord a volatile chloride, 

 as the product of distillation is in general colourless, there is 

 usually no difficulty in distinguishing the sulphuret of arsenic 

 from that of antimony. If we cannot distinguish them, or sup- 

 posing both metals to be present, the addition of nitrate of silver 

 in excess, filtration and consequent application of ammonia to 

 the filtered liquor, will show the presence or absence of arsenic. 



I consider the method which I have now described as a valu- 

 able addition in toxicological researches. It is very easily per- 

 formed j it separates the arsenic from substances which interfere, 

 and render, in other methods, the results fallacious ; indeed, in 

 some cases, prevent the arsenic, though in considerable quantity, 

 from being detected; such as the presence of organic matter, 

 which, as in Marshes process, occasionally causes annoyance 

 by the frothing up of the materials, and consequent rise of the 

 mixture into the tube. 



