644 Dr. J. Emerson Reynolds [May 28, 



Silicon Analogues of Carbon Compounds. 



The points of physical resemblance between silicon and carbon are 

 of small importance compared with the much deeper rooted resem- 

 blance in chemical habits which exists between the two elements. 

 This is expressed in the periodic table of the elements as in the 

 following diagram : — 



Na=23, Mg=24, Al=27, Si=28, P=81, S=P,2, Cl=35'5 

 Li = 7, Be = 9, B=ll, C=12, N=14, 0=1G, F=19 



where silicon is represented as the middle term of a period of seven 

 elements of increasing atomic weights, just as carbon is the middle 

 term of the previous period. The fact is these two electro-negative 

 or non-metallic elements play leading parts in the great drama of 

 nature, silicon dominating that which has to do with dead matter, 

 while carbon is the great organ-building and maintaining element of 

 all living things. While each carries on the work to which it is best 

 suited under existing terrestrial conditions, they both go about it in 

 somewhat similar ways and each one shows tendencies to overstep the 

 border line and perform the other's part. This tendency is for 

 various reasons nuich more marked in the case of carbon, but I hope 

 to show you presently that silicon is by no means out of touch with 

 Mving things, and further that it exhibits capacities which render it a 

 potential element of life under other conditions of our planet, but 

 more especially at a much higher level of temperature. 



I do not propose to dwell in much detail on the remarkable 

 parallelism of some silicon and carbon compounds, but must refer 

 shortly to a few of them, and the oxides naturally come first. 



I have just stated that we know with certainty only one oxide 

 of silicon, the dioxide SiOo. This is analogous to the highest 

 oxide of carbon — the well-known COo which plays so important a 

 part in the lives of animals and plants. This familiar carbon com- 

 pound is a gas under ordinary conditions, but here is some of it in the 

 form of snow. Alongside of this is a vessel containing some finely 

 divided Si02 or sihca. They are rather like in appearance but they 

 differ greatly in volatiUty. The COg snow speedily resumes the 

 gaseous state at ordinary temperature, but silica requires a very high 

 temperature indeed even for fusion, however when heated in an 

 electric furnace, the oxide can not only be fused but volatilized. In 

 the fused state it can be fashioned into various shapes and affords 

 most convenient vessels for many purposes, as they are not liable to 

 crack on sudden heating or cooling, and are not attacked by any 

 acid except hydrofluoric acid. 



As the difference between the atomic weights of the elements 

 carbon and silicon is only 16 units, silicon dioxide should not differ 

 in volatility nearly so much as it does from carbon dioxide. This and 



