IN CASES OF POISONING. 267 



4. The organic matter is introduced, together with 

 the whole of the liquid, into a capacious tubulated 

 retort, and about an equal weight of rock-salt, or of 

 fused common salt, in small fragments, added. The 

 retort is connected with a tubulated receiver, furnished 

 with a delivery-tube which dips into water. A quan- 

 tity of (tested) sulphuric acid, sufficient to decompose 

 the whole of the chloride of sodium, is then poured 

 upon the mass through a funnel tube passed into the 

 tubulure of the retort. When the intumescence and 

 evolution of hydrochloric acid have ceased, the con- 

 tents of the retort are heated to boiling, the receiver 

 being kept thoroiighly cool. All the arsenic is thus 

 distilled off as chloride, especially towards the last, in 

 proportion as the contents of the retort become more 

 concentrated, on which account the distillation should 

 be carried pretty far. The arsenic is converted into 

 chloride, even when it exists in the mass, in the form 

 of sulphide. The distillate may be at once introduced 

 into Marsh's apparatus. It is safer, since some organic 

 matter might possibly have passed over, to precipitate 

 the arsenic from the solution by sulphuretted hydro- 

 gen, and to treat the precipitate as directed above. In 

 the same way the small quantity of arsenic contained 

 in the water in which the hydrochloric acid was con- 

 densed, may be precipitated. This method seems to 

 be the most simple and sure, to distil the mass directly 

 with concentrated hydrochloric acid, instead of salt 

 and sulphuric acid, and the arsenic passes over as 

 chloride. 



Marsh's apparatus has the following simple con- 

 struction : a is a two-necked bottle capable of holding 

 , or at most 1 pint. Both necks are fitted with new 

 perforated corks, which must be perfectly tight. 

 Through one of these, the funnel tube b is passed air- 

 tight, and through the other, the bent tube c, which is 

 expanded at c into a bulb about an inch in diameter. 



