280 Dr. Hofmann on [May 16, 



analogies not less prouiiiieiit than those which are observed with 

 the elements chlorine, bromine, and iodine. 



The type Ammonia offers another interesting illustration of the 

 influence which the progress of Organic Chemistry exerts upon the 

 Mineral Department of the science, and of the unexpected support 

 which some of the mineral theories have received from the deve- 

 lopment of our ideas regarding the constitution of organic sub- 

 stances. 



Soon after Sir Humphry Davy's immortal discoveries of the 

 alkali-metals, chemists were led by the extraordinary analogy of the 

 salts of these metals with those of ammonia, to assume in tlie latter 

 a metallic substance similar to potassium and sodium.* Numerous 

 experiments were made to isolate this metallic principle from the 

 ammoniacal salts ; and the resources of electricity, which had ex- 

 hibited such wonderful powers in the hands of Sir H. Davy, were 

 not appealed to without result. The metal itself, it is true, was not 

 isolated ; but a compound or alloy was obtained, containing nitrogen 

 and hydrogen, and the metallic character of which was indisputable. 

 If the electric current be passed into a solution of ammonia floating 

 upon a layer of mercury in such a manner, that the positive pole of 

 the battery merely dips into the ammonia, while the negative pole 

 is immersed in the mercury, a very remarkable phenomenon is 

 observed ; the mercury begins to swell up and is gradually converted 

 into a mass of buttery consistence, but retaining a perfect metallic 

 lustre, while pure nitrogen gas arising from the oxidation of am- 

 monia makes its appearance at the positive pole.*]" Removed from 

 the influence of the battery, the altered mercury soon resumes its 

 original appearance, losing at the same time hydrogen and ammonia 

 in the proportion of one equivalent of the former (H) to one of 

 the latter (N Hg). It was therefore argued that the mercury owed 

 the alteration of its properties to its being associated with hydrogen 

 and ammonia, that is with N H4 ; and since mercury in its combina- 

 tions never retains any metallic appearance, except in its alloys called 

 amalgams, that is in its combination with metallic substances, che- 

 mists considered themselves entitled to attribute metallic characters 

 also to the hypothetical association of nitrogen and hydrogen, 

 represented by the formula N H4 = Am, for which, forthwith, the 

 name of Ammonium was proposed. 



* The analogy of the salts of ammonia and those of the fixed alkalies, and 

 especially the isomorphism of the salts of ammonia and potassa, was illustrated 

 by numerous specimens upon the Lecture-table. Ammonia-alum and potassa- 

 alum, sulphate of ammonia and sulphate of potassa, chloride of ammonium and 

 chloride of potassium, &c. &c. 



t The ammonium-amalgam was produced on a small scale by the action 

 of the electric current. 



