ON THE PRECIPITATION OP CLAY SUSPENDED IN WATER. 129 



16. On the Influence of various Substances in Accelerating the 

 Precipitation of Clay suspended in Water. By William 

 Ramsay, Esq., Tutorial Assistant in Glasgow University Labo- 

 ratory. With a Note by Prof. Ramsay. (Read March 8, 1876.) 



(Communicated by Prof. Ramsay, F.R.S., V.P.G.S.) 



It has been noticed by several observers that clay suspended in 

 water settles more quickly if the water is salt than if it is fresh. 

 This fact is contrary to what would naturally be supposed — namely, 

 that suspended matter should settle more easily in a liquid of low 

 than in one of high specific gravity. 



The earliest notice which I have been able to find relating to 

 this subject, is a note by Skey in the ' Chemical News ' for 18G8, 

 p. 160, in which he advances the following hypothesis to explain 

 the phenomenon. 



After taking notice of the fact that those salts which accelerate 

 the precipitation of clay are too stable to be decomposed by mere 

 contact with it, he suggests that such salts have a strong affinity 

 for water compared with that of clay for water. They therefore 

 tend to abstract water from the clay, and cause it to coagulate and 

 settle. In corroboration of this he instances the fact that iron 

 ferrocyanide is thrown down by numerous salts ; that silica is 

 precipitated from its solution in ammonia by chloride of ammonium ; 

 and that nitrate of baryta is precipitated by nitric acid. 



In the ' Chemical News ' for August, 1874, Durham advances an 

 electric hypothesis ; he supposes that clay, in falling through water, 

 " generates electricity by friction, and, as water is a bad conductor, 

 the difference in potential between the clay and the water remains 

 for some time, hence they are mutually attracted ; but when an 

 acid or salt are added, the liquid becomes a good conductor, the 

 potentials are equalized, and the clay falls." 



Durham also states that in solutions of the same salt of different 

 strengths, the rate of settling is in the order of the specific gravity 

 of the solutions, and that clay remains longest suspended in the 

 liquid of highest specific gravity. 



Before reading either of these papers my attention was drawn to 

 this subject by a communication from Air. Peter Robertson to the 

 Geological Society of Glasgow. It struck me that a probable solu- 

 tion of the question was to be found in the relative amounts of heat 

 absorbed by various salts in passing into solution. 



Does the rapidity of precipitation of clay in • solutions of salts 

 bear any relation to the absorption of heat by the salts in passing 

 into the liquid state? In order to answer this question, some 

 experiments were made which I shall now proceed to describe. 



Some very fine clay was procured, which on being put into water 

 broke up of its own accord into very minute particles. A number 

 of solutions of different salts were prepared, and the specific gravi- 



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