288 VETEEINAKY TOXICOLOGY 



added. This gives a reddish-brown coloration with traces 

 of copper, and a reddish-brown precipitate with larger 

 amounts, and is a more delicate test than the blue ammonia 

 coloration. 



The nitric acid leaves undissolved mercury. This is then 

 dissolved in hydrochloric acid with the addition of a little 

 potassium chlorate, and after boiling off the chlorine is 

 tested by Eeinsch's test with copper, or by adding stannous 

 chloride solution, which precipitates insoluble mercurous 

 chloride (calomel), and on warming converts this into 

 mercury as a black deposit of finely divided metal. 



The table (p. 289) summarises the operations set forth 

 above. 



The delicacy of the method is amply sufficient for toxico- 

 logical purposes, and even for the recognition of traces 

 which can hardly have medico - legal interest. Thus 

 ^^ grain of lead can be separated and recognised by 

 sulphuretted hydrogen when originally contained in 2 ounces 

 of organic matter.* With this amount of organic matter a 

 positive reaction for lead may be anticipated with certainty. 

 For mercury a proportion of ^tt grain in 2 ounces can 

 sometimes be recognised, at others not — that is, the figure 

 quoted is an extreme lower limit. The limit for copper is 

 yItj grain, and that for zinc ^^ grain, each in 2 ounces. 

 The same figures apply to the detection of these metals 

 when all the organic matter is burnt off by heating with 

 strong sulphuric acid. 



GROUP C. 



This group comprises non-volatile organic poisons, of 

 which the most important are the alkaloids and glucosides 

 derived from poisonous plants. Of less importance are 

 non- volatile phenols, such as tannin ; organic acids, such 

 as picric and oxalic ; bitter principles, such as santonin and 

 cantharidin ; and synthetical drugs, such as antipyrin, 

 sulphonal, and veronal, which do not play an important part 

 in the toxicology of animals. 



* See Lander and Winter, loc. cit. 



