212 PRESENT PROBLEMS OF INOROANIO CHEMISTRY. 



however, that at low tciiiperatures compounds could be formed m 

 which one of the elements Avould possess a greater valency than that 

 usually ascribed to it; and also that double compounds of greater 

 complexity would prove stable. Valency, indeed, appears to be in 

 many cases a function of temperature; exothermic compounds, as 

 is ^vell knowai, are less stable the higher the temperature. The sud- 

 den cooling of com]Dounds produced at a high temperature may pos- 

 sibly result in forms being preserved which are unstable at ordinary 

 temperatures. Experiments have been made in the hope of obtaining 

 compounds of argon and helium by exposing various elements to the 

 influence of sj^arks from a pow^erful induction coil, keeping the walls 

 of the containing vessel at the temperature of liquid air, in the hope 

 that any endothermic compound which might be formed Avould be 

 rapidly cooled and \vould survive the interval of temperature at 

 wdiich decomposition Avould take j^lace naturally. But these experi- 

 ments have so far yielded only negative results. There is some indi- 

 cation, however, that such compounds are stable at 1,500°. It might 

 be hoped that a study of the l)ehavior of the nonvalent elements 

 would have led to some conception of the nature of valency, but so 

 far no results bearing on the question have transpired. The condi- 

 tion of helium in the minerals from which it is obtainable by heat is 

 not explained, and experiments in this direction have not furnished 

 any positive information. It is ahvays doubtful wdiether it is advis- 

 able to publish the results of negative experiments, for it is always 

 possible that some more skilled or more fortunate investigator may 

 succeed where one has failed. But it may be chronicled that attempts 

 to cause combination between the inactiA'e gases and lithium, j^otas- 

 sium, rubidium, and cjcsiiun have yielded no positive results, nor 

 do they appear to react with fluorine. Yet conditions of experiment 

 play a leading part in causing combinations, as has been well shown 

 by Moissan with the hydrides of the alkali metals, and by Guntz, 

 with those of the metals of the alkaline earths. The proof that 

 sodium hydride possesses the formula NaH, instead of the formerly 

 accepted one, removes one difliculty in the problem of valency, and 

 SrlL falls into its natural position among hydrides. 



A fertile iield of inorganic research lies in the investigation of 

 structure. While the structure of organic compounds has been eluci- 

 dated almost completely, that of inorganic compounds is practically 

 undeveloped. Yet efforts have been made in this direction which 

 appear to point a way. The nature of the silicates has been the sub- 

 ject of research for many years by F. W. Clarke, and the way has 

 been opened. Much may be done by treating silicates with approj^ri- 

 ate solvents, acid or alkaline, which differentiate between uncombined 

 and combined silica, and which in some cases, by replacement of one 

 metal by another, gives a clue to constitution. The complexity of the 



