2l6 



SCIENCE PROGRESS 



Such being the conditions that govern chemical change in 

 gases, it is important to consider how they may be applied to 

 liquids, and especially to those organic liquids in which 

 isomeric change is most frequently observed. Two types of 

 change may be broadly distinguished. In the first type all the 

 constituents which take part in the interaction are conductors, 

 so that the action proceeds rapidly, and is often almost instan- 

 taneous ; in this category must be included — in addition to the 

 action of (aqueous) acids on (impure) metals— the large range 

 of cases in which electrolytes interact, as in the precipitation 

 of silver chloride from aqueous solutions of silver nitrate and 

 of potassium chloride. In the second type the constituents 

 include materials which do not conduct ; the passage of the 

 current is then hindered, and the progress of the chemical 

 change is retarded, in many cases to such an extent that the 

 action appears to be absolutely stopped, in spite of the fact 

 that all the materials which are usually necessary for inter- 

 action are present. In this category may be included many of 

 the interactions of organic chemistry, such as the bromination, 

 nitration, and oxidation of carbon compounds. In most of 

 these changes the carbon compound and the brominating or 

 oxidising agent are non-electrolytes, which can only enter into 

 an electric circuit as depolarisers to discharge the products of 

 electrolysis. The action is then dependent on the presence of 

 an impurity or catalyst to provide the electrolytic element 

 of the circuit, and even when this is forthcoming, there still 

 remains the difficult)' of conveying the current between the 

 non-conducting electrodes. In bromination it is probable that 

 a trace of (moist) hydrogen bromide usually serves to start 

 the action, the carbon compound acting as a depolariser for 

 electrolytic bromine and the bromine as depolariser for electro- 

 lytic hydrogen. Thus in the bromination of ethylene 



In the interaction of chlorine and a saturated hydrocarbon, 

 such as methane, the action would be 



