Intelligence and Miscellaneous Articles. 469 



ously work in this way with all substances which are capable of 

 spreading over each other, were it not that there are some which 

 cannot be made to form a thin plate on a framework. In the case 

 of these liquids, the experiment is made by replacing the free lamina 

 by one almost as thin and as stretched, which is formed by letting 

 the liquid extend on a carefully cleaned glass plate. 



One of the two substances may be extended as a thin lamina on 

 another liquid, and the lamina thus produced may be worked with like 

 a free one. These two latter methods have this advantage over the 

 use of a skeleton, that the surface of contact between the two liquids 

 is smaller, and that they mix or combine less easily ; thus the expe- 

 riment is in many cases greatly facilitated. 



The author has investigated a great number of substances from this 

 point of view. He has found it to be an extremely general fact, 

 and that there is probably no liquid, excepting perhaps mercury, 

 which has not the property of spreading as a thin lamina on a great 

 number of liquids, and in regard to which other substances do not 

 enjoy the same property. The following are the principal results to 

 which this investigation has led. 



1. When one liquid can extend in a thin lamina upon the surface 

 of another liquid, the second can never extend in the same way over 

 the first. 



2. Two liquids whose reciprocal adhesion is greater than the co- 

 hesion of that one of them in which this property is smallest, have 

 always the property that a drop of the one with the smaller cohesion 

 extends upon the other. 



3. A drop of the latter retains its shape when placed on the surface 

 of the former, and becomes coated with a thin layer of the first 

 liquid. 



4. All liquids which satisfy the above conditions as to the magni- 

 tude of adhesion, may be arranged in a series in which each antece- 

 dent liquid spreads on the surface of a succeeding one, and never 

 conversely. 



5. This series is the same as that obtained when the same liquids 

 are arranged in the order of their capillarity-constants 



\2ric 2 2 y / 



the smallest constant being first. 



6. The rapidity with which this extension takes place is almost 

 proportional to the interval which separates them in the Table. 



7. The phenomenon is the more distinct the less the miscibility 

 of two liquids and the greater the difference of their cohesions. 



8. The extension of a liquid on its own surface may be effected by 

 placing a drop at a high temperature upon the surface of the liquid 

 at a lower temperature. 



9. The greater the cohesion of a liquid the more difficult is it to 

 obtain a clean surface. This is the case with water for instance, on 

 which almost all liquids can extend. 



The substances on which the author has worked are the following, 



