IN CASES OF POISONING. 265 



acidified with dilute sulphuric acid, and chlorine-gas 

 is passed, to saturation, into the mass thus coagulated, 

 as in 1. 



3. The organic matter cut into shreds, is treated 

 with about as much pure concentrated hydrochloric 

 acid as is equal to the weight of the dry substances 

 contained in the mass ; enough water is then added to 

 form a thin paste. The dish is heated on a water- 

 bath, the contents stirred every five minutes, and about 

 30 grs. of chlorate of potassa (free from lead) added to 

 the hot liquid until it has become clear yellow, homo- 

 geneous, and limpid. After being heated for some 

 time longer, the solution is strained through a moist- 

 ened filter of white paper, free from smalt, the residue 

 washed upon the filter with hot water till the washings 

 are no longer acid, the whole liquid poured together 

 into a porcelain dish, and evaporated to about 1 pound 

 upon the water-bath. 



The solution obtajned by one of these methods is 

 poured into a cylindrical glass or into a flask, and a 

 slow stream of sulphuretted hydrogen gas passed into 

 it to complete saturation. All the arsenic is thus pre- 

 cipitated as sulphide, Its precipitation is much pro- 

 moted if the liquid be heated for about half an hour to 

 50 or 60, while the gas is passing, and allowed to 

 cool before the stream of gas is discontinued. When 

 saturated, the liquid is allowed to remain for twenty- 

 four hours in a closed vessel. The precipitate which 

 is then deposited has generally, even if much arsenic 

 be present, a dirty, undecided, grayish-brown color.* 

 The greater portion of the solution is poured off, and 

 the precipitate thrown upon the smallest possible filter 

 of Swedish paper ; free from smalt, upon which it is 



_* If lead, copper, mercury, or antimony were present, the preci- 

 pitate would also contain the sulphides of these metals, for which 

 it would have to be particularly examined. 



23 



