ON THE SUBSIDENCE OF PARTICLES IN LIQUIDS. 



HEAD AT XEW UAVEX MEETIXG, NOYEMBER 15, 18S3, 



While connected with the State Geological Survey of California, lS60-'64, uiy attention was 

 turned to the relations of saline and alkaline waters to the precipitation of suspended matter. 

 There were abundant means of observation in the field, but no laboratory experiments were made. 

 Soon after the republication by the Eay Society, in 18G6, of Robert Brown's observations on the 

 movements of minute solid particles in liquids, I began a series of experiments on these " Brown- 

 ian movements" in their relations to sedimentation, but unfortunately I have now no systematic 

 record of the experiments made previous to February, 1875, since which time the experiments have 

 been much extended and systematic records have been kept of many of them. In 1877 I pub- 

 lished some of the observations in their relations to agriculture [Wth Ann. Kep. Com. State Board 

 of Ayr., p. 73-83), and in 1880 further observations in their sanitary relations — on the action of 

 muddy water on sewage — Public Health Papers and Reports, vi, 334), and in 1881, in a lecture (not 

 published further than in ordinary newspaper reports), I further discussed the matter in connection 

 with the problem of the jetties at the mouth of the Mississippi River. 



Since 1877 the experiments have been much expanded and have gone on along several lines of 

 investigation. They extend to a considerable number of clays, soils and other suspended matter, 

 and the records and notes have now become somewhat voUiminoas. Inasmuch as prolonged time is 

 an element in some of the experiments, and as this meeting enables me to exhibit some of the speci- 

 mens to the academy, I take the occasion to report on some of the observations made and inferences 

 deduced from these long-continued observations and still unfinished experiments. 



It is a matter of common observation that fine clays and muds may remain long suspended 

 in fresh water, but it is commonly believed that if the water be left at rest complete sedimentation 

 takes place within a few weeks or months at most, leaving the water clear; that salts of many 

 kinds hasten the settling, and that also acids hasten it. Some writers have stated that dilute 

 alkalies retard it and may prolong it even indefinitely, and numerous observers have noticed that 

 during the subsidence of clays in perfectly still fresh water they are often disposed iu layers or 

 strata of different degrees of density, giving to the liquid different degrees of opacity. 



In this paper I do not purpose to review the history of our knowledge of this subject, nor to 

 discuss the published observations or experiments of others ; that is left for a future paper. It will 

 better serve my present purpose to discuss my own experiments (with tlie exhibition of a few ot 

 my specimens), with only so much allusion to the labors of others who have wrought iu the same 

 field as is necessary for an understanding of my own work. 



If clays containing some fine sand, as most clays do, are thoroughly mixed with pure fi-esh 

 water and then allowed to stand iu perfect quiet iu a suitable vessel, a portion, including all the 

 coarser particles, soon falls to the bottom, but a considerable portion remains longer suspended. 

 The water may become nearly clear in a day or two, or finer material suflQcient to render the 

 liquid opaque in vessels three or more iuches in diameter may remain suspended for weeks. 



In these latter cases the liquid usually becomes disposed in strata ; that is, the suspended mat- 

 ter will not fade gradually in density from the bottom upwards through regularly diminishing 



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