TllANSACTIONS OF SECTION B. 679 



4. On the Manv/adure oj Soda and Chlorhie. By W. Wkldon, F.R.S. 



5. On the Clipmi'/ifni of tho Natural Slh'cafn/t, 

 Jly Professor T. Snnniv Hint, LLJl, F.ILS. 



Tlie jrenesis of the crystalline' stnUifii'd rocks, iiicliulinj^ tlio finidameiital 

 irranitc ami t ho .succeeding cryt-tiillino enzoic sclii.st>, is a .sultjoct for llit; clicniist, 

 witliont wlioM' aid tlic natural history student, ^vllt'ther ho styles hiuisclt" 

 jiiiiuTalogist or ^'coloii'ist, can never hope to Sdlve this ^rrcat riddlo of freop'ny. 

 Till' intervention of water, as taught hy Werner, in the formation of the granitic 

 sulistratuin is now conceded, and we are ])repared for a rt'statenient of Ne})tuiiisni 

 iqion an igneous basis, as I have elsewhere attenipte<l under the name of the 

 cit'iutic liypothesis. The ciiief clieniical ])rol)leni involved tlier^'in will he evident 

 wlirji we consider the composition of the rocks already referred to. 'riw.'se, 

 excluding carbonates, quartz, and non-silicated oxides, are made up essentiaily of 

 silicates, hydrous or anhydrous of a few bases, chielly jjotash, soda, lime, magnesia, 

 I'eiTdiis oxide, and alumina. Tlie most im])ovtant distinction among tliese is tliat 

 Lt'tween aluminous and non-aluminous silicates, due to tlie reiuly sulubilily and 

 wide dill'usion of salts of the protoxide bases in natural waters, and to the stability 

 luid insolubility of the silicates of alumina. Of natural aluminous silicates wo 

 have a series from simple hydrous and aniiydrous species, through the pinites and 

 inuscovites and daniourites, in wliieh the oxygen ratio of ])i'otoxido to aluiaiua is 

 1 : L', 1 : 0, or 1 : G. AVe then come to the great zi>olite and ftddspar grnuj) in 

 which it is 1 : o, and to silicates like epidote, garn"t, magiiesian micas and 

 chlurites, in which it becomes I : I and even 2 : ]. That of the feldspar, which 

 we may call the normal ratio, is finiud also in aluminates, and its signiticauco is 

 clear to the chemist. .Muminous double silicates with this ratio are formed in 

 soluti(jns in presence of excess of alkalies, and appear as natural ri'sulls of aijue'ous 

 actiiin on igneous basic rocks as seen in basalts, in amygdaloids, and in volcanic 

 mud in the deep sea. Tlie studies of JUmstMi and those of Daubree throw great 

 light on this process. The simultaneous production in many cases of protoxide 

 silicates like pectolite, gyrolite, okerite, and apophyllite, is nox'; to be considered. 

 All of these are non-magnesian, but by reaction on dissolvcnl salts of n)agnesia take 

 up this base by exchange. Hence ser])entines, chrysolite, pyroxene and tale. 



The decomposition by heat of alkaline solutions of alumina and silica, in some 

 cases with depositions of quartz and producti(.)ns of more basic solutions which 

 react with magnesiau salts, explains the origin of aluminous silicates with excess 

 of protoxide bases. The power of alkaline silicates in aqueous solution to hold 

 dissolved various metallic oxides, throws light in the production of oxides of the 

 spinel and corundum groups. 



The origin of simple aluminous silicates and others with small amounts of 

 protoxide is found in the diagenesis of the kaolin from subaerial decay of feldspathic 

 rocks, soluble silicates of the zeolitic type often intervening. 



In the various reactions set forth in this paper it was said that we have, by the 

 working of known chemical laws, an explanation of the genesis of the great 

 groups of natural silicates and the basis of a rational system of mineralogy and of 

 litbology. 



i»;i 



6. On the Liquefaction of Oxi/rfen and the Dcnsiti/ of LitjiiUl Hydrogen. 

 By Professor James Dewar, M.A., F.B.S. 



7. On the Physical Gomtants of Solutions. By Professor W. L. Goodwin, 

 B.Sc, and Profos.sor D. H. Marshall, M.A., F.B.S.E. 



Previous experimenters have prepared solutions containing m molecules of 

 anhydrous chlorides to n molecules of water. Such solutions do not contain 

 equal numbers of molecules of the salts in equal volumes of the solutions. The 



