642 Dr. J. Emerson Reynolds [May 28, 



WEEKLY EVENING MEETING, 



Friday, May 28, 1909. 



Hi8 Grace The Duke of Northumberland, K.G. P.O. 

 D.C.L. Sc.D. F.R.S., President, in the Chair. 



J. Emerson Reynolds, Esq., M.D. Sc.D. F.R.S. M.R.L 



Recent Advances in our Knoivledge of Silicon and of its Relations 

 to Organised Structures. 



I have placed on the table before you a magnificent natural 

 crystal of the colourless mineral quartz, which is the property of the 

 Royal Institution. This is the oxide — dioxide — of the element Silicon, 

 about which I have the honour to address you this evening. This 

 oxide of Silicon is — as you are doubtless well aware— commonly called 

 Silica, and is met with in Nature in many conditions, either colour- 

 less as in this "rock crystal" or coloured in the black quartz, in 

 common topaz and amethyst, and uncrystalline in agate and flint. 



Not only is Silicon widely diffused in Nature in the many forms of 

 its oxide, but it also constitutes between one-third and one-fourth of 

 the original and non-sedimentary rocks — of which the solid crust of 

 the earth largely consists — in these cases being chemically combined 

 with Oxygen and various metals forming natural Silicates. In this 

 diagram we have a necessarily very rough estimate of the relative 

 proportions in which the chief constituents are present. 



The Earth's Crust. 



Approximate average Composition of uon-sedimientary Rocks. 



Oxygen . . . . about 47 per cent. 



Silicon .. .. „ 28 „ 



Aluminium . . . . ,, 8 ,, 



Iron . . . . „ 7 „ 



Calcium and Magnesium ,, 6 ,, 



Alkali Metals . . „ 4 „ 



The crust of the earth is in fact a vast assemblage of silicon com- 

 pounds, and the products of their disintegration under the influence of 

 water and other agents produces the various forms of clay, sand and 

 chalk which constitute so large a portion of the earth's surface. 



The solid crust of the earth is actually known to us for but a very 

 few miles down — thirty at most — our deepest mines being mere 

 scratchings on its surface ; but, so far as known, practically all its 

 constituents are fully oxidised, and this is probably true at much 

 greater depths. During aeons past oxygen has been absorbed as the 



