THE REVIVAL OF INORGANIC CHEMISTRY. 297 



we shall ever have a very extensive chemistry of the " hydro-silicons 

 and tlieir derivatives." Among the compounds of other elements self- 

 linkage occurs in but few cases and is limited in extent. 



3. It is a highly important property of carbon compounds that their 

 molecules tend to preserve their individuality; they generally do not, 

 though there are exceptions, spontaneously avail themselves of oppor- 

 tunities for condensation, whether by polymerization or by union of 

 two or more molecules with separation of water or ammonia. The so- 

 called double and triple union between carbon atoms only exception- 

 ally leads to spontaneous polymerization, while with silicon this latter 

 is apparently the rule. The important carbonyl group, C^=0, the char- 

 acteristic group of organic acids, aldehydes, and ketones, shows but 

 little tendency to polymerize, while organic hydroxyl compounds are 

 usually stable and do not spontaneously give rise to ethers or acid 

 anhydrides. The silicou analogue of carbonyl, Si = O, on the contrary, 

 appears to polymerize with great ease. The ethers of carbonic acid 

 are well known, but the metasilicic ethers, those of the type SiO (OR).., 

 appear to exist only as polymers. The silicic acids, too, show a marked 

 tendency to condense by dehydration and pass spontaneously into 

 complex bodies. It is easy to see what would have been the result if 

 carbon behaved like silicou. Instead of the innumerable sharply 

 defined organic acids, aldehydes, ketones, and alcohols, each produced 

 by a definite synthetic process, each reaction would give rise to an 

 almost inextricable mixture of condensation products, carbon dioxide 

 would be a solid like silica, and organic chemistry would be scarcely 

 further advanced than is the chemistry of silicon. This tendency of 

 carbon compounds to simplicity in reaction, each molecule acting as if 

 it were alone present, has been, therefore, an important factor in 

 facilitating the growth of organic chemistry. 



4. Another feature of carbon which plays an important part is the 

 ease with which intermediate or transition products can be formed. 

 It is much easier to limit reactions in the case of carbon compounds 

 than in others. Compare, for example, the action of chlorine on OH 4 

 aud SiH 4 . 



5. The tendency to dissociation, both hydrolytic and electrolytic, is 

 in general less marked among carbon compounds, whence it is easier to 

 control the course of a reaction and to exclude changes of a sponta- 

 neous nature. Finally, the carbon compounds show but little tendency 

 to the formation of so-called molecular addition products, of which the 

 metal-ammonias, the double salts and the compounds with water of 

 crystallization are examples, the rational interpretation of which is 

 difficult. 



A full consideration of the peculiarities of carbon which have facili- 

 tated the synthesis of such vast- numbers of organic compounds would 

 be beyond the scope of this address. The above are the most impor- 

 tant, and their relative absence in the majority of elements explains 



