C. GENERAL PHYSICS. 139 



of carbureted leases. In these the flame is found to contain 

 carbon in the form of lamp-black. The particles of carbon 

 become incandescent so long as they remain in the flame. 

 But lamp-black reflects very little light, or none at all ; there- 

 fore the absence of light polarized by reflection seems very 

 natural in the flames of carbureted gases. This, however, is 

 but a partial explanation, as he himself subsequently shows. 

 He states that he has examined with the polariscope the 

 flame of phosphorus, burning both in the shade and in the 

 bright sunshine, and has not been able to perceive the least 

 appearance of polarization. So also in the case of the flame 

 issuing from the top of the cupola of a coke furnace; neither 

 at Bisrht nor in bright sunshine was he able to detect the 

 slightest trace of polarization. Yet when, at the end of the 

 operation, the furnace door was opened, and a thick bluish 

 smoke escaped, instead of flame, at the top, this smoke, 

 strongly illumined by the still glowing interior, gave decided 

 evidences of a polarized light. 7 A, XLVII.,206. 



GALVANIC POLARIZATION IN LIQUIDS FREE FROM GAS. 



Professor Helmholtz has for a long time been investigating 

 the question as to the cause of the apparently unlimited du- 

 ration of the polarizing current which, although feeble, arises 

 when a Daniell's zinc-copper element is closed by a water-de- 

 composition cell with platinum electrodes. He shows that 

 the battery can maintain an unceasing feeble current be- 

 tween the platinum electrodes, not merely when the liquid is 

 in contact with air, but also when in contact with a perfectly 

 closed vessel, if its electrodes are saturated with oxygen, and 

 its liquid holds oxygen in solution. A simple test apparatus 

 being devised, he states that he has seen a current main- 

 tained for weeks together by electrolytic convection alone, 

 under the influence of a limited stock of oxygen in a hermet- 

 ically isolated liquid ; and hydrogen is much more eflicient 

 than oxygen. When the plates and the liquid are copiously 

 saturated with electrolytic-ally developed hydrogen, the de- 

 composition cell behaves toward feebler currents, for hours, or 

 even for days, as a non-polarizable element similar to a so- 

 lution of silver between silver electrodes. The constancy of 

 the current, however, comes to an end when, through con- 

 vection of the hydrogen, its store in one of the plates begins 



