CHEMICAL TOXICOLOGY 293 



tile having a number of cup-shaped depressions. Before 

 evaporation it is advisable to run the extract through a small 

 dry filter-paper, in order to remove traces of watery solution. 

 The problem of detecting the organic poison now con- 

 fronts the analyst, and is beset with difficulty, for many 

 reasons, of which may be stated as prominent — 



(a) The invariable presence of traces of impurity derived 

 from the original organic material, such as fats, carbo- 

 hydrates, and traces of protein resolution products of basic 

 character. Whether a poison is present or not, there is 

 always left after evaporation a more or less considerable 

 smear of yellowish to brown colour, which reacts with such 

 general alkaloidal reagents- as phosphomolybdic acid, and 

 has reducing properties. If, however, an organic poison 

 is present in fair quantity — as, for instance, about -g^ or 

 upwards of a grain, the difficulty on account of such 

 normal impurity is diminished. 



(b) In many cases characteristic or distinctive reactions 

 are lacking. This holds particularly with bitter substances 

 and glucosides. 



Purification. — It is theoretically easy to devise methods 

 for the purification of any of the special types of organic 

 poison — in fact, it is hard to carry out, because the 

 process is wasteful, and therefore in dealing with a trace 

 there is risk of entirely losing it. This event befalls very 

 often. A residue may show a certain reaction in an in- 

 complete or masked fashion, leading to a strong suspicion 

 of the presence of a particular poison. After apipropriate 

 purification the test may fail. This does not mean of 

 necessity that the substance was absent, but, on the other 

 hand, may point to it having been present in small quan- 

 tities of such order as not to point to poisoning. In this 

 sense such an observation is valuable. 



Alkaloids which are strong bases may be purified by 

 dissolving the residue in a dilute acid (acetic or sulphuric), 

 and shaking the solution with solvents, which more or less 

 fully remove adventitious impurities of a neutral, acid, or 

 feebly alkaline nature. Thereafter the acid liquid is suitably 



