458 



Prof. Guthrie on Drops, 



[Recess, 



typical of extensive classes, rather than as being connected with one another 

 in immediate chemical relation. They were — 



Water. Oil of turpentine (turpentol). 



Alcohol. Benzol. 



Acetic acid. Glycerine. 



Acetic ether. Mercury. 



Butyric acid. 



These several liquids were allowed to drop under the same conditions, 

 from the bottom of a hemispherical platinum cup. The arrangement of the 

 apparatus was quite similar to that described in Part I., the ivory ball being 

 replaced by the platinum cup, and the overflow of the cup being deter- 

 mined by strips of paper bent over its edge. The case of mercury is the 

 only one which requires some explanation. A few years ago I noticed the 

 fact that mercury which holds even a very little sodium in solution has 

 the power of " wetting " platinum in a very remarkable manner. The 

 appearance of the platinum is quite similar to that presented by amalga- 

 mable metals in contact with mercury. But the platinum is in no wise 

 attacked. Further, the amalgam may be washed off by clean mercury, 

 and the latter will also continue to adhere equally closely to the platinum. 

 All the phenomena of capillarity are presented between the two. The 

 surface of the mercury in a platinum cup so prepared is quite concave ; and 

 a basin of mercury may be emptied if a few strips of similarly prepared 

 platinum foil be laid over its edge — ^just as a basin of water may be emptied 

 by strips of paper or cloth, and under the same condition, namely that the 

 external limb of such capillary siphon be longer than the internal one. 



I generally use this curious property of sodium-amalgam for cleaning 

 platinum vessels. It enables us now to examine the size of drops of mer- 

 cury under conditions similar to those which obtain in the case of other 

 liquids*. After the cup had been used for the other liquids, its surface 



^ In regard to the above-mentioned property of sodium, the following observations 

 may be of interest. At first the explanation naturally suggests itself, that the effect 

 wrought by the sodium may be due to an absorption of oxygen, in consequence of the 

 oxidation of the sodium, the consequent diminution of the gaseous film between the 

 two metals, and the resulting excess in the superior pressure of the air. This, however, 

 cannot be the true explanation, because it is found that tlie perfect contact between the 

 two, or " wetting," takes place equally well in an atmosphere of nitrogen, carbonic acid, 

 or in vacuo. Hence, if I may venture upon a guess, imsupported by experimental evi- 

 dence, I should be rather disposed to assign the phenomenon to the reducing action of 

 nascent hydrogen derived from the contact of sodium with traces of water. Perhaps 

 even the least oxidizable metals are covered with a thin film of oxide, which is reduced 

 by the nascent hydrogen at the same moment that the mercury is presented to the re- 

 duced metal. It is found that iron, copper, bismuth, and antimony are also wetted by 

 mercury if their surfaces are first touched with sodium amalgam. Not only do the 

 latter metals lose this power on being heated (as we might expect, in consequence of 

 their superficial oxidation), but platinum, from which the adhering mercury film has 

 been wiped by the cleanest cloth, or from which it has been driven by heat, also loses 

 the power. It is true that the surface of clean platinum is supposed to condense a 



