< \KHON AND THE HYDROCARBONS ;343 



more or less resemble wax in their properties, although ordinary oils 

 and wax generally contain oxygen in addition to carbon and hydrogen, 

 but in relatively small proportion. There are also a few hydrocarbons 

 which have the appearance of tar as, for instance, metacinnamene and 

 gutta-percha. Those liquid hydrocarbons which boil at a high tempera- 

 ture are like oils, and those which have a low boiling point resemble 

 rthrr, whilst the gaseous hydrocarbons in many of their properties are 

 akin to hydrogen. All this tends to show that, in hydrocarbons phy- 

 sically considered, the properties of solid 11011- volatile charcoal are 

 strongly modified and hidden, whilst those of the hydrogen predominate. 

 All hydrocarbons are neutral substances (neither basic nor acid), but 

 under certain conditions they enter into peculiar reactions. It has 

 been seen in those hydrogen compounds which have been already con- 

 sidered (water, nitric acid, ammonia) that the hydrogen in almost all 

 cases enters into reaction, being displaced by metals. The hydrogen of 

 the hydrocarbons, it may be said, has no metallic character that is to 

 say, it is not directly 22 displaced by metals, even by such as sodium and 



viscosity varies with the temperature and nature of the liquids, and, in the case of solu- 

 tions, changes with the amount of the substance dissolved, but is not proportional to it. 

 S,. thai, for example, with alcohol at 20 the viscosity will be 69, and for a 50 p.c. solu- 

 tion 1C>(>, the viscosity of water being taken as 100. The volume of the liquid which passes 

 through by experiment (Poiseuille) and theory (Stokes) is proportional to the tune, 

 the pressure, and the fourth power of the diameter of the (capillary) tube, and inversely 

 proportional to the length of the tube ; this renders it possible to form comparative esti- 

 mates of the coefficients of internal friction and viscosity. 



As the complexity of the molecules of hydrocarbons and their derivatives increases 

 by the addition of carbon (or CH 2 ), so does the degree of viscosity also rise. The exten- 

 eries ot 'investigations referring to this subject still await the necessary generalisation. 

 That connection which (already partly observed) ought to exist between the viscosity 

 and the other physical and chemical properties, forces us to conclude that the magnitude 

 of internal friction plays an important part in molecular mechanics. In investigating 

 organic con-pounds and solutions, similar researches ought to stand foremost. Many 

 observations have already been made, but not much has yet been done with them; the 

 bare tacts and some mechanical data exist, but their relation to molecular mechanics has 

 not been cleared up in the requisite degree. It has already been seen from existing data 

 that the viscosity at the temperature of the absolute boiling point becomes as small as 

 in ga 



-' In a number of hydrocarbons and their derivatives such a substitution of metals 

 for the hydrogen maybe arrived at by indirect means. The property shown by acetylene, 

 (11,. and its analogues of forming metallic derivatives is in this respect particularly 

 characteristic. Judging from the fact that carbon is an acid element (that is, gives an 

 ac id anhydride with oxygen), but comparatively slightly acid (because carbonic acid is 

 not. at all an energetic acid; compounds of chlorine and carbon, even CC1 4 , are not 

 decomposed by water as is the case with phosphorus chloride, and even silicic chloride 

 or boric chloride, although they correspond with acids of but little energy), one might 

 expect to find in the hydrogen of hydrocarbons this faculty for being substituted by 

 metals. The metallic compounds which correspond with hydrocarbons are known under 

 the name of organo-metallic compounds. Such, for instance, is zinc ethyl, Zn(C 

 which corresponds with ethyl hydride or ethane, C.^H , where two atoms of hydrogen 

 have been exchanged for one of zinc. 



