C. GENERAL PHYSICS. 173 



avoidance of all less elevated conducting divergences within 

 striking distance of the conductor, and especially such dan- 

 gerous divergences of this character as gas-pipes connecting 

 with the general gas-main, and therefore forming good earth 

 contacts. 12 A, XII., SO. 



SUKFACE TENSION OF LIQUIDS. 



Cintolesi has experimented on the relation which the sur- 

 face tensions of various liquids sustain to each other under 

 various conditions. Of these conditions, temperature is one 

 of the most important. A drop of olive, almond, or castor 

 oil placed upon distilled water at 100 retains its lenticular 

 form, and does not spread into a film. At 65 the drop be- 

 gins to flatten, and at 50 the fihn forms, but is silver white, 

 showing no color. If, however, water at 100 be allowed to 

 fall on a surface of cold oil, a membrane is formed, which at 

 first shows colored rings, but which soon contracts into a 

 drop as it cools. Examining solutions of various salts in the 

 cold, he observed the well-known wide differences of behavior 

 with diff*erent oils. Repeating tlie experiments at 40, he 

 found that even so slight an elevation of temperature com- 

 pletely reversed the phenomena in many cases, making the 

 surface tension of the solution less than that of the oil. He 

 nsed alcohol, ether, and benzene, copaiba balsam, the fixed 

 oils of olive, castor, almond, and linseed, and the ethereal oils 

 of cinnamon, clove, mint, lavender, and bitter almonds. AVith 

 cinnamon and clove oils there was at first a spreading out 

 into a film ; then the film was ruptured, forming numerous 

 flat drops, which became round, and showed phenomena re- 

 sembling ebullition, finally breaking up into smaller particles. 

 The influence of the vapors of certain liquids on these films 

 is often remarkable. A drop of ammonia on the end of a 

 rod, when brought near an oil-drop resting quietly on the 

 surface of water, causes its rapid expansion. If the experi- 

 ment be made on a glass disk covered with a layer of water 

 on which the oil-drop rests, the expansion begins when the 

 rod is six or seven centimeters distant, and on closer ap- 

 proach the water is driven out and the oil-drop fiills to the 

 glass. Examining the phenomena under the microscope, 

 Cintolesi found, 1st, that the films always contain swell- 

 ings, which produce holes by their rupture, thus causing the 



