PRESENT PROKLEMS OF INORGANTC CHEMISTRY. 218 



molecules of inor^'anic compounds, -which are usually solid, forms 

 auoUu'r bar to invcstio-aiion. It is clear that sid[)liuric acid, to choose 

 a common instance, possesses a very complicated molecule, and the; 

 fused nitrates of sodium and potassium are not correctly represented 

 b}' the simple fornuda^ NaNO.j and KNO... x^ny theory of the struc- 

 ture of their derivatives must take such facts into consideration; but 

 Ave api")ear to l)e <>'ettinii' nearer the elucidation of the molecular 

 weio;hts of solids. Ao'ain. tlie comjjlexity of solutions of th" most 

 connnon salts is maintained by many in vest i pi tors. For example, a 

 solution of cobalt chloride, while it undoubtedly cont'SHns, amono- 

 other constituents, simple molecules of (\)C1„, also consists of ions of 

 a complex cliaracter, such as (CoC^l,)". And what holds for cobalt 

 chloride also undoul)tedly holds for many similar comjiounds. 



In determining the constitution of the com|)ounds of carbon, stereo- 

 chemistry has played a great part. The ordinary structural fornndu' 

 are now universally acknowledged to l)e only [)ictorial, if, indeed, that 

 word is legitimate. Perhaps it would be better to say that they are 

 distorted attempts at pictures, the drawing of which is entirely free 

 from all rules of perspective. But these fornudie may in almost 

 every case be made nearly true pictures of the configuration of the 

 molecules. The benzine fornnihi, to choose an instance which is by 

 no means the simplest, has been shown by Collie to l)e inutated by a 

 model which represents in an mistrained maimer the behavior of 

 that body on treatment with reagents. But in the domain of inor- 

 ganic chemistry little progress has been made. Some ingenious ideas 

 of the geologist Sollas on this jjroblem hav^e hardh^ received the atten- 

 tion which they deserve. Perhaps they may have been regai'ded as 

 too speculative. On the other hand, Le BeFs and Pope's proof of the 

 stereo-isomerism of certain compounds of nitrogen. Pope's demon- 

 stration of the tetrahedral structure of the alkyl derivatives of tin, 

 and Smiles's syntheses of stereo-isomeric sulphur compounds give us 

 the hope that further investigation will lead to the classification of 

 many other elements from this point of view. Indeed, the field is 

 almost virgin soil, but it is well worth while cultivatino-. There is 

 no doul)t that the investigation of other oi-gano-metallic comj)ounds 

 will result in the discovery of stereo-isomerides; yet the methods of 

 investigation capable of separating such constituents have in most 

 cases still to be discovered. 



The number of chemical isomerides among Inorganic com])ounds 

 is a restricted one. Werner has done much to (ducidate this sub- 

 ject in the case of complex annuonia dei'ivatives of metals and their 

 salts; but there appears to be little doubt that if looked for, the 

 same or similar phenomena would be discoverable in Compounds 

 with nuich simplei- formuhe. The two forms of So.,, sulphuric an- 

 hydride, are an instance in i)oint. No doubt formation under dif- 



