6 



posed fluid suspected to contain the poisonous metal ; in which case, 

 as was formerly shown by Sir H. Davy in his Bakerian lecture, the 

 metal held in solution is deposited in the form of crystals, on the 

 negative surface. The zinc was usually employed in the form of 

 foil j the platina was, in some cases, a small crucible, or a spatula ; 

 but more frequently platina foil was used. It is generally necessary 

 to mix a few drops of acid with the metallic compounds that are 

 subjected to this test, and that are placed in contact with the pla- 

 tina: on applying the zinc foil, the platina will soon become coated 

 with the reduced metal. 



The author then enters into the detail of his experiments on the 

 efficacy of his method in the detection of arsenic, mercury, lead and 

 copper, in their different states of oxidation and saline combina- 

 tions ; and of the precautions necessary to be observed in the case 

 of each metal. He was enabled to detect the presence of arsenic, 

 by the exhibition of its characteristic properties, when only the 

 500dth part of a grain of that metal was deposited on the platina ; 

 and in some instances could appreciate the 2500dth part of a grain, 

 by the application of appropriate tests. 



The author next ascertained that the electro-chemical method is 

 competent to the detection of very minute quantities of the differ- 

 ent metals, when their compounds are mixed with various vegeta- 

 ble and animal substances. Thus, the presence of arsenic would 

 readily be discovered when mixed with all the ordinary articles of 

 diet, — such as wheaten flour, bread, starch, rice, potatoes, peas, 

 soup, sugar, vinegar, gruel, tea, milk, eggs, gelatine, and various 

 kinds of wine ; also when mixed with the principal secretions of 

 the alimentary canal, as bile and saliva. Arsenious acid mixed 

 with butter, lard and oils, or with sheep's blood, or ox bile, was de- 

 tected with great ease. Similar results were afforded by corrosive 

 sublimate, the acetate of lead, and sulphate of copper, added in 

 small quantity to the most complicated mixtures of organic sub- 

 stances. In some instances where the common tests do not act at 

 all, or only act fallaciously, the electro-chemical method acts with 

 the greatest certainty. 



Anniversary Meeting, Nov. 30th. 

 DAVIES GILBERT, Esq. President, in the Chair. 

 On this occasion the President delivered the following Address : 

 Gentlemen, 



/ Having now, for the last time, to address you in reference to the 

 'oss of eminent persons sustained by the Society in the preceding 

 year, I cannot but congratulate you on the difference between the 

 list now read, and that which we had the misfortune to hear twelve 

 months ago. Several individuals of great distinction, of extensive 

 acquirements and of splendid talents, are undoubtedly brought before 

 ws on the present occasion : but advanced age or long absence from 



