527 



The phosphorus-compounds accordingly hold a position inter- 

 mediate between the nitrogen-compounds on the one hand, and the 

 arsenic- and antimony-series on the other. It cannot, however, 

 be denied that the phosphorus-bodies exhibit rather a tendency 

 towards the arsenic- and antimony-series, than towards the nitrogen- 

 group. 



This cannot surprise us, when we consider the close analogies 

 which phosphorus and arsenic present in many other directions. 

 Both phosphorus and arsenic form well-characterized polybasic 

 acids ; the acids of antimony are not yet sufficiently investigated, 

 but the acids of nitrogen, which are better examined, are all found 

 to be monobasic. The equivalent numbers, too, of phosphorus, 

 arsenic, and antimony, present a remarkable connexion, the difference 

 between those of phosphorus and arsenic, and those of arsenic and 

 antimony being virtually the same 



Ph S P horUS 31 | difference 44, 



Arsenic 75 i 



Antimony 120 } difference 45, 



whilst the equivalent of nitrogen stands altogether apart from the 

 rest. 



The same relative position of the elements nitrogen, phosphorus, 

 arsenic, and antimony, may also be traced in their hydrides, 



H 3 N H 3 P H 8 As H 3 Sb. 



Ammonia is a powerful alkali ; phosphoretted hydrogen unites 

 only with hydrobromic and hydrioclic acids, whilst in arsenietted 

 and antimonietted hydrogen, the power of combining with acids has 

 altogether disappeared. In these hydrogen- compounds the gra- 

 dation of properties is indeed even more marked than in their 

 trimethylated and triethylated derivatives. On comparing the 

 terminal points of the series, ammonia and antimonietted hydrogen, 

 we cannot fail to be struck by the dissimilarity of properties 

 which at the first glance appears to limit the analogy of the two 

 compounds to a mere parallelism of composition. 



In the methylated and ethylated derivatives of these compounds, 

 the intensity of the chemical tendencies in general is so much 

 raised, that the gradation is no longer perceptible to the same 

 extent. 



