66 VETEEINAEY TOXICOLOGY 



Chemical Diagnosis. — Silver is dissolved in the nitric 

 acid extraction process, and separated according to that 

 scheme, as sulphide along with the other metals {q. v.). In 

 seeking for silver the sulphides are to be extracted with 

 warm nitric acid (not hydrochloric as in the ordinary 

 routine), and the characteristic tests for silver performed on 

 the solution of the nitrate. The precipitation by hydro- 

 chloric acid of flocculent silver chloride, colourless, but 

 blackened on exposure to light, is characteristic. It should 

 be further shown that the chloride is soluble in excess of 

 ammonia, whereby it may be separated from the sparingly 

 soluble lead chloride, which does not dissolve in ammonia. 

 Prom the ammonia solution silver chloride is reprecipitated 

 by acidifying with nitric acid. 



Other tests are also delicate, but most of them not very 

 characteristic. Thus potassium chromate from a neutral 

 solution gives reddish-yellow silver chromate, but confusion 

 with the yellow chromates of lead and barium is possible. 

 Potassium iodide gives yellow silver iodide, which in very 

 small traces is not easily distinguished from other insoluble 

 iodides, such as those of bismuth, copper, and lead. 



Phosphates and arsenites give yellow precipitates of the 

 corresponding silver salts, and arseniates give brown silver 

 arseniate. All these are only formed in the absence either 

 of free acid or ammonia, and are of little value in practical 

 toxicology. 



Silver also coats copper in Eeinsch's test, and on warming 

 the copper with dilute nitric acid both metals dissolve 

 to form the nitrates. Hydrochloric acid precipitates silver 

 chloride from the solution of the mixed nitrates. 



BARIUM. 



Forms and Occurrence. — Barium is the most toxic 

 of the metals of the alkaline earth series — calcium, strontium, 

 and barium — and cannot replace calcium in its relations to 

 life ; for instance, in respect to blood coagulation, and bone 



