302 THE REVIVAL OF INORGANIC CHEMISTRY. 



oxygen atoms, and in which nitrogen may be either tri- or pentavalent. 

 Some of these are given in the books "as if they were gospel truth. 

 Briihl, who has investigated the question by physical methods, sug- 

 gests that the hydrogen atom is not directly united to any part of the 

 N0 3 radical, but is rotating around it and possibly combined with each 

 oxygen atom in succession, a view approaching that of Werner. There 

 are at least five formulas proposed for this simple acid. For the 

 familiar potassium chloroplatinate, K 2 Pt01,;, there are four constitu- 

 tional formulas seriously advocated at present. It may be K 2 =PtCl 6 , 

 with octavalent platinum; 



KC1==CK >ptci 



KCl=01 >iTUl2 ' 



with tetravalent platinum and trivalent chlorine, as required by Bern- 

 sen's theory; (PtCl 6 )K 2 in the sense of Werner's theory, the two potas- 

 sium atoms being combined with the PtCl 6 as a whole, or it may be a 

 molecular compound in which two molecules KC1 as wholes combine 

 with PtCl 4 as a whole. The formulas suggested for most minerals are 

 pure guesswork. The silicates are usually written as if containing the 

 group Si=0, by analogy with carbonyl, 0=O, yet there is not a single 

 silicate in which this assumption rests on any experimental evidence, 

 and the little we do actually know of the chemical behavior of silicon 

 speaks against it. Such formulas, if not purely speculative and devoid 

 of all basis and all value, as they frequently are, at best do not repre- 

 sent structure in the sense that the best established organic formulas 

 do: they are at most reaction formulas only, or they represent partial 

 molecules, in the same way that OH may stand for benzene (C 6 H 6 ) or 

 HPO3 for a metaphosphoric acid. The attempt to interpret the double 

 salts and halides, the compounds with water of crystallization or 

 hydration, the metal-ammonias, the peculiar compounds of the zeolites 

 described by Friedel, and other so-called molecular compounds, in the 

 sense of the valence hypothesis, seems almost hopeless without taking 

 such liberties with it as to render it nearly useless, and without making 

 assumptions of very narrow and limited applicability. One may well 

 question whether this hypothesis must not be very considerably quali- 

 fied before it can be taken as the basis of a general theory of the 

 structure of inorganic compounds. 



One of the most striking indications of a revival of inorganic chem- 

 istry is the recent attempt of Werner to break away from the bonds of 

 the organic structure theory as applied to inorganic compounds and to 

 establish a more general theory in which valency plays a comparatively 

 insignificant role. The arguments on which Werner's hypothesis is 

 founded are too numerous and elaborate to be presented here. Suffice 

 it to say that it was primarily based on that peculiar class of bodies 

 known as the metal-ammonias, consisting of metallic salts, combined 

 with usually six or four molecules of ammonia, and in which the ammonia 



