1820.] extiacied from Pyrites at Fahluii. . 1.9 



we cannot be too mucli on our guard against adopting and pro- 

 pagating changes, which are not necessary in a nomenclature 

 once admitted, since long custom renders it difficult to correct 

 even a bad nomenclature. It will be, perhaps, objected to me 

 • that sulphuretted, seleniuretted, and teliuretted hydrogens 

 actually possess some of the principal characters of acids. I 

 allow this. But what confusion in the nomenclature would be 

 produced if we thought proper to call every substance an arid 

 which in a combination may act the part of an electro-negative 

 body ! Do we call every substance an alkali which is capable of 

 acting the part of an electro-positive body ; that is to say, a 

 base { 



11. General Observations relative to the Properties of Seleniu/u^ 

 The existence of a body whose properties constitute, so to 

 speak, the transition from the non-metallic combustible bodies 

 to the metal is surely a very interesting phenomenon ; while this 

 body possesses some of the characteristic properties of the 

 metals, for example, the metallic lustre ; it is destitute of others 

 equally essential, for example, of the power to conduct electricity 

 and heat. In fact, as there is no positive line of^separatioii 

 between the chemical properties of these two classes of bodies, 

 it is probable that none ought to exist between their external 

 properties. 



We have seen that selenium is more analogous to sulphur than 

 to any other body, and next to sulphur, it resembles tellurium ; 

 so that it lies between these tno bodies. But it is from its 

 properties that we must determine in which of the classes we 

 must place it, whether among the metals, or along with sulphur, 

 phosphorus, boron ; that is to say, the class of substances to 

 which I have ventured to give the name of uieialloids. In itself 

 it is indifferent in which of the two classes we place it, since the 

 limits between them are not determinable, and since selenium 

 possesses to such a degree the characters of both, that we may 

 place it with equal justice in either of the two. The metallic 

 lustre and the specific gravity have been considered as the cha- 

 racteristics of the metals ; but the last of these has ceased to be 

 a cliaracter, because we are now acquainted with metals v.hich 

 are lighter than water. Nothing remains but the lustre ; and I 

 beheve that if sulphur and phosphorus possessed the metaOic 

 histre, nobody would hesitate to place them among the metals. 

 As selenium possesses this property in a high degree, and as it 

 must of necessity be placed in one of the two classes, I conceive 

 that we may arrange it in preference among the electro-negative 

 metals, that is to say, among those which produce acids. It 

 will begin the series in making the transition from sulphur and 

 phosphorus to arsenic. 



The number of simple combustible bodies has been lately 

 augmented by three ; two of which with equal, If not with greater 



b2 



