PROCEEDINGS OE GEOLOGICAL SOCIETIES. 



145 



pig-iron produced in various furnaces containing a considerable portion of 

 silicon, sometimes even as much as eight per cent., and frequently three 

 or four per cent. The presence of it in iron modifies the properties of 

 the latter considerably. It combines readily enough with copper. If vre 

 take a little copper or iron in a more or less divided state, say in the form 

 of filings, and mix these filings with common sand (a compound of silicon 

 and oxygen), and add an excess of charcoal, making a mixture of the 

 three, and let the amount of charcoal and sand be such that, when we ex- 

 pose the mixture in a crucible to a high temperature sufficient to melt the 

 copper or the iron, as the case may be, there should be sufficient of this 

 mixture to retain the metal diffused through the mass, and then expose 

 the mixture to a high temperature for a few hours — all the silica, under 

 the conjoined influence of the carbon and the metal, is decomposed, the 

 carbon laying hold of the oxygen, and escaping in the form of carbonic 

 oxide, while the silicon is set free, combining with the metal. Common 

 copper treated in this way — heated with sand and charcoal for a long 

 time — undergoes a great change in its external appearance. It has no 

 longer the red colour of copper, but has the appearance of bronze, which 

 is a mixture of copper and tin. It is so like the bronze of which our guns 

 are composed, that an inexperienced eye would not distinguish the one 

 from the other when they are side by side. It is a very valuable alloy, so 

 that you see that silicon may play a very important part even in the 

 common arts of this country. To give another illustration of the fusion 

 of silica. Platinum is a metal which requires a very high heat for its fu- 

 sion. If we heat silicon in contact with platinum at a high temperature, 

 no change will take place ; but add a bit of charcoal, and repeat the expe- 

 riment. The silica instantly becomes reduced under these conditions, and 

 the silicon set free combines with the platinum, forming a very fusible 

 compound. 



The lecturer added a few more words concerning the proofs — the mine- 

 ralogical or geological proofs — relating to the aqueous origin of crystallized 

 silica, and they are very conclusive. Let us look at our mineralogieal 

 cabinets, and examine the specimens of quartz which we find therein. One 

 was exhibited, a very small one, which, when examined minutely, was 

 found to surround a mineral called haematite, consisting of peroxide of 

 iron and water — a mineral which loses its water at a very low temperature. 

 There it was, embedded in the quartz, clearly showing that the quartz 

 never could have been exposed to a high temperature. Here is another 

 mineral, carbonate of iron, embedded in the quartz, and the existence of 

 this and the peroxide clearly shows that that quartz never could have been 

 exposed to a high temperature, and supports the conclusion at which we 

 have arrived touching its aqueous origin. Then we find incrustations 

 which lead to the same conclusion. 



With regard to amorphous silica, there is no doubt whatever about its 

 aqueous origin. We can trace its origin in the clearest and most distinct 

 way. In Iceland, for example, it is abundantly produced in the geysers. 

 Here is a specimen which has been obtained from that source. Then, 

 again, here is a specimen of granite from Iceland, on which is deposited a 

 thin film of silica, having a pearly lustre. There is no one who will ven- 

 ture to say that that could have been thrown down on to the granite 

 except by the agency of water. The specimens are very small in them- 

 selves, but, nevertheless, they speak very eloquently of the origin of silica, 

 and tell an important tale, small as they are. Here is a very characteristic 

 specimen showing the occurrence of crystalline quartz in two states on the 



VOL. VII. V 



I! 



