1890.] On the Tension of recently formed Liquid Surfaces. 281 



most probable that the metal exists in the ash as silver chloride. No 

 other heavy metal than iron and silver could be detected. The most 

 scrupulous care was taken in proving that the silver did not come 

 from any of the vessels or reagents employed. 



By carefully made assays, both in the dry and liquid way, it was 

 found that the silver was present to the extent of about 1 part in 

 107,200 of the ash, or between a fourth and a third of a Troy ounce to 

 the ton of 2240 pounds. This is rather a smaller proportion than 

 was found in the Cotopaxi ash, which contained about 1 part for 

 83,600, or two- fifths of an ounce per ton. In both eruptions the fall 

 of considerable quantities of ashes at points on the sea coast so distant 

 from the respective volcanoes as Guayaquil and Bahia de Caraguez 

 indicates that in the aggregate very large absolute amounts of silver 

 must have been ejected and dispersed. 



These two appear to be the only cases in which silver has been 

 detected among the materials thrown out by volcanoes. Although the 

 fact is well known that the chain of the Andes has for centuries 

 yielded this metal" in great abundance, it is worthy of notice that, to 

 the depths as yet reached by mining work, Ecuador is less rich in 

 valuable minerals, and especially the precious metals, than any other 

 of the South American States. 



II. " On the Tension of Recently Formed Liquid Surfaces." 

 By Lord Rayleigh, Sec. R.S. Received February 13, 

 1890. 



It has long been a mystery why a few liquids, such as solutions of 

 soap and saponine, should stand so far in advance of others in 

 regard to their capability of extension into large and tolerably 

 durable laminae. The subject was specially considered by Plateau in 

 his valuable researches, bat with results which cannot be regarded as 

 wholly satisfactory. In his view the question is one of the ratio 

 between capillary tension and superficial viscosity. Some of the 

 facts adduced certainly favour a connexion between the phenomena 

 attributed to the latter property and capability of extension ; but the 

 " superficial viscosity " is not clearly defined, and itself stands in 

 need of explanation. 



It appears to me that there is much to be said in favour of the 

 suggestion of Marangoni* to the effect that both capability of exten- 

 sion and so-called superficial viscosity are due to the presence upon 

 the body of the liquid of a coating or pellicle composed of matter 

 whose inherent capillary force is less than that of the mass. By 



* ' Nuovo Cimento,' vol. 5-6, 1871-72, p. 239. 



