THE SUBSIDENCE OF PAIiTIGLES IN LIQUIDS. 167 



that many, if not most, clays behave very difierently in hot water from what they do in cold, 

 and dlflerent clays differ in behavior in hot water. 



Some clays which go to pieces easily in cold water, and which settle slowly if the water re- 

 mains cold, settle rapidly if the water be raised to near the boiling-point. Some such clays which 

 have been experimented upon, which will remain suspended in large quantity for many days if 

 kept cold or at ordinary temperatures, if the water be gradually heated, when a certain tempera- 

 ture is reached the clay suddenly flocculates or curdles, and settles in a very bulky, mobile mass 

 long before the water begins to boil, and during the boiling there is this constant tendency to floc- 

 culate, the suspended matter behaving much as it does in the presence of certain chemicals, to be 

 noted later. If the heat be removed and the liquid allowed to cool slowly, the phenomena are re- 

 versed. While hot, much of the sHsi)ended matter curdles and falls in a very bulky, mobile mass, 

 which if shaken soon falls back again until the water reaches a certain reduction of temperature, 

 when, if the material be shaken, it will require several days for any part to become so nearly clear 

 as the upper part would be in a few minutes if hot. I think it probable that some of the colors 

 described in the hot springs of the Yellowstone region may be related to the behavior of clays in 

 hot water. 



Again, freezing affects the suspension. If water holding suspended particles be frozen solid 

 and then be thawed again, it is rendered much clearer by the operation. The mud becomes largely 

 disposed along certain lines of crystallization in the ice, and if this be slowly thawed in the quiet, 

 it falls and does not rise again. In one set of my experiments the water in which a red ferrug- 

 inous clay was suspended froze partially solid, a portion of the liquid being entirely surrounded by 

 ice. In the liquid the suspended matter was ultramicroscopic, but in the ice the red material was 

 concentrated in visible particles along certain lines, curiously disposed relative to the crystal- 

 lization and to the inclosed air-bubbles. Stereoscopic photographs show the arrangement in the 

 mass, but drawings are very unsatisfactory. 



In one such case, when the liquid, much cleared by the freezing, was placed near a window 

 where the sun struck it a little while each day, it soon became turbid again, possibly by convection 

 currents caused by the sun's heat; but similar specimens melted in the dark and kept in the dark 

 remained as clear as the freezing had made them. Changes in ink by freezing are familiar to all, 

 and probably due to the same cause. 



Some clays, if thoroughly dried, and then moistened again, and then frozen and thawed in a 

 wet state, behave very differently in water before and after such freezing. 



The fallen sediment from different clays varies greatly in hardness and tenacity, the difier- 

 ences not following the relative proportions of sand in the original material under experiment. 

 With some samples, even of very fine clay, the suspended portion may be very large and the 

 dense turbidity remain a long time, and yet the sediment which does fall be very firm in a day or 

 two, while others may fall speedily into a bulky mass as mobile as the water itself, which shrinks 

 and is compacted very slowly indeed in the water. Some sediments, when they have stood a few 

 days or weeks in the liquid from which they have subsided, are so firm that it requires much and 

 long agitation to again diffuse them through the water; others, after several years' standing, may 

 be entirely diffused by a few seconds' agitation. 



It is obvious that each and all of these various facts have their geological significance, and 

 phenomena immediately suggest themselves where they certainly or possibly play a part. 



Thus far I have only described the behavior of clays and suspended matter to fresh water, 

 and in many of my experiments distilled water has been used. 



