490 Dr. Andrew Fyfe on the Detection of Arsenic, 



The method which I now follow in conducting the process is 

 to pour the suspected fluid into a flask with a wide mouth, to 

 which is adapted a cork having two apertures in it. To one of 

 them is fitted a bent tube, one end of which terminates in the 

 flask immediately below the cork ; the other end terminates in 

 a tube containing distilled water, and placed in a cold fluid. 

 Into the other aperture is placed a cork. Oil of vitriol is now 

 poured in, and the mixture is boiled for some time ; after which 

 cb-ied sea-salt is thrown in rapidly, and the cork is quickly re- 

 placed. The distillation is then continued for some time, taking 

 care to keep the fluid, in which the tube is placed, as cool as 

 possible. Instead of one, I sometimes employ two or even three 

 tubes, with distilled water, in each of which the product of 

 distillation is condensed, and all of which, if necessary, are 

 tested for arsenic. When any of the tissues is to be examined, 

 it is introduced into the flask with oil of vitriol, and boiled for 

 some time, or till it entirely disappears. Sea-salt is then thrown 

 in, and the process is conducted as described. 



As the trfinsmission of SH through the product of distillation 

 in general gives satisfactory evidence of the presence or absence 

 of arsenic, it is scarcely necessary to have recourse to any other 

 test. It may however be more satisfactory to have recourse to 

 others, and of these by far the best is nitrate of silver. It is to 

 be added as long as it causes precipitation. The fluid is then 

 to be shaken and filtered, by which the whole of the chlorine 

 and hydrochloric acid is removed. After this a rod dipt in solu- 

 tion of ammonia is held over the filtered liquor. If arsenic is 

 present the yellow film appears. 



In using SH the operator requires to be on his guard, be- 

 cause the presence of uncombined acid causes the decomposition 

 of the gas, and consequent deposit of sulphur, which may, by 

 one not accustomed to observe precipitates, be mistaken for yel- 

 low arsenic. 



It may be objected to this method of detecting arsenic, that 

 it will not succeed when the arsenical compound is in the state 

 of sulphuret ; with King's yellow, for instance, which is some- 

 times taken as a poison. This must be admitted, when the sul- 

 phuret is pure. In one trial, in which sulphuret, prepared from 

 an arsenical solution by precipitation, after being well washed, 

 was treated with oil of vitriol and sea-salt, as described, the 

 distilled fluid did not show indications of arsenic by the usual 

 tests. 



This, however, is not the case with the commercial sulphuret, 

 which, in all the trials that I have made with it, has afibrded a 

 fluid by distillation with oil of vitriol and sea- salt, in which 

 arsenic was easily detected. This is owing to its containing 

 arsenious acid. Accordingly, when King's yellow was washed 



