258 Dr. J. Kerr's Electro-optic 



acid was not noticeably stronger or weaker electro-optically 

 than the chlorine solution. 



Summary. 



29. The principal results of the experiments are briefly 

 summed up in the following statements;, the numbers of the 

 corresponding articles being attached in each case for re- 

 ference. 



The elementary bodies bromine, phosphorus, sulphur, all 

 in the liquid state, are purely and strongly positive (3) . 



The hydrocarbons are nonconductors and purely positive, 

 without known exception. The induction effected up to this 

 time is a mere beginning in such an immense field ; but it 

 includes examples of the alcohol radicals or their hydrides, of 

 the benzol series, of the olefines, the paraffins, and the tere- 

 benes ; also cinnamol and naphthalin. Among the hydro- 

 carbons, great density is generally accompanied by high 

 electro-optic power (4). 



The common alcohols are negative as a class. From the 

 higher members downwards, the negative electro-optic power 

 diminishes regularly, till it passes, in the last step of the series 

 (ethyl to methyl), from feeble negative to feeble positive. 

 Distilled water also is distinctly positive (5). 



Of the series of fatty acids, those liquid at ordinary tem- 

 peratures are in constant opposition of sign to the correspond- 

 ing alcohols ; they are also very much stronger. Of those 

 that are solid at ordinary temperatures, two have been ex- 

 amined in a state of fusion, and are found, on the contrary, to 

 be strongly negative (6, 7). 



Of other alcohols and acids, the allyl, benzyl, cinnvl al- 

 cohols are negative ; the diatomic glycol and the triatomic 

 glycerin are feebly and impurely negative ; phenol is distinctly 

 positive, though in its chemical relations rather an alcohol 

 than an acid : the oleic and lactic acids are both positive, the 

 former strong, the latter very feeble (8). 



The oxides of ethyl and amyl are purely negative, and 

 stronger than the corresponding alcohols. Amyl oxide is a 

 moderately good insulator, and one of the best negative dielec- 

 trics yet known (9). 



The haloid ethers are purely positive, and rise in power 

 from one series to another in the order I, Br, 01 ; they 

 generally rise also in power from lower members upwards. 

 Some of them show an extraordinary increase of insulating and 

 electro-optic powers as the experiment proceeds. Amyl chloride 

 is one of the best positive dielectrics known : amyl bromide 

 also is very strong CIO, 11, 12). 



