124 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



is inversely as the resistance, copies faithfully the varying 



pressure of the sound-waves, and transmits them along the 



line. 



4. Electrolysis. 



Ayrton and Perry have published an account of an elab- 

 orate series of experiments on ice as an electrolyte. As a 

 result of their experiments, they state that the capacity per 

 cubic centimeter of ice at 13.5 C. is 0.002 micro-farad, 

 and the specific inductive capacity is 22,160 (that of air 

 being called unity), while that of water at 8.7 is about 

 2240 times this amount. Commencing with ice at 13.6 C, 

 the temperature was allowed to rise, and the conductivity 

 determined by galvanometer readings. From these a very 

 regular curve was deduced, which shows that the conduc- 

 tivity increases regularly, and that there is no sudden rise 

 in passing from the solid to the liquid state. The same ap- 

 paratus was also used to determine the electro-motive force 

 of polarization-currents at different temperatures. 



Helmholtz has published a note containing the results 

 of a research made at his suggestion by Root to ascertain 

 whether in galvanic polarization the electrolytic gases re- 

 mained on the exterior or actually penetrated the platinum. 

 The experiments show a very rapid penetration of the plati- 

 num, so that if for only five minutes the platinum plate ex- 

 perimented on and one to the right of it were connected 

 with a Daniell's cell, a condition of polarization was devel- 

 oped between it and a plate to the left. 



Bertrand has experimented on the electrolytic preparation 

 of the metals, and has prepared aluminum, magnesium, cad- 

 mium, bismuth, antimony, and palladium from their aqueous 

 solutions in this way. The current employed should be 

 strong, and the concentration of the solution carefully reg- 

 ulated. 



5. Electric Spark. 



Spottiswoode has described the new enormous induction 

 coil made for him by Apps, which is capable of giving sparks 

 42 inches long. It has two primary coils one used for long 

 sparks, the wire being GG0 yards long and 0.09G inch diam- 

 eter ; the other, for fat sparks, has 84 pounds of wire, instead 

 of G7. The secondary wire is 2S0 miles long, and forms 

 341,850 turns. Tn the two central sections the diameter of 



