276 Dr. Hofmann on ' [May 16, 



phoric and arsenic acids the tribasic character is well marked ; 

 with antinioiiic acid it is less pronounced ; and nitric acid is generally 

 considered as a monobasic acid : but the progress of science will, I 

 have no doubt, confirm our suspicion tiiat the nitrogen-acid is 

 likewise of a tribasic character. The chlorides and bromides, cor- 

 responding to the oxides of nitrogen, phosphorus, antimony, 

 and arsenic, also exhibit, within certain limits, similar analogies.* 



Again, these four elements unite with hydrogen, and the com- 

 pounds thus produced have a similar composition ; they are all 

 terhydrides. 



Ammonia NIT3 



Phosphoretted Hydrogen . . . PH3 



Antimonetted Hydrogen . . . SbHg 



Arsenetted Hydrogen .... AsHg 



So far the analogy appears to be complete. Extraordinary dis- 

 crepancies, however, are observed in the properties of these hydro- 

 gen-compounds, for although they are all gases at the common 

 temperature, although they all possess a marked odour, and are 

 more or less inflammable, we find that ammonia is soluble in water, 

 imparting a strongly alkaline character to this solution ; while the 

 three other compounds, phosphoretted, antimonetted, and arsenetted 

 hydrogens are insoluble in water, and without the slightest alkaline 

 reaction. Again, ammonia when coming in contact with acids, 

 absorbs these bodies with the greatest avidity, producing a series of 

 well marked, mostly crystalline, compounds, which are called salts of 

 ammonia, or ammoniacal salts, and of which sal ammoniac and sul- 

 phate of ammonia are familiar illustrations. Antimonetted and 

 arsenetted hydrogen, on the other hand, have never been combined 

 with acids ; and in the case of phosphoretted hydrogen, only one 

 salt-like compound, the hydriodate of phosphoretted hydrogen is 

 known, which latter certainly presents considerable analogies with 

 the salts of ammonia. 



Sulphate of Ammonia NH3, HSO4 



Hydriodate of Ammonia NH3, HI 



Hydriodate of Phosphoretted Hydrogen . PH3, HI 



The want of similarity observed in the general characters of 

 ammonia and the hydrogen-compounds of phosphorus, antimony, and 

 arsenic, has always been an obstacle in the way of considering the 

 four elements in question as members of the same natural family. f 



* For the purpose of illustration specimens of Nitrogen^ Phosphorus, Anfi- 

 monyj and Arsenic, and of their oxides, chlorides, and bromides were upon the 

 table. 



t The preparation and the principal properties of ammonia, phosphorcUed, 

 aiUimonetled, and arsenetted hydrogen were experimentally exhibited. The 



