THE SUBSIDENCE OF PARTICLES IN LIQUIDS. 171 



iiiyl coiuiliidBil "thiit the earthy miitter is deposited more suddenly than would be the case if it 

 depended on the check of velocity alone" (Eqmrt on the ITydrnnlic.s and Phyaics of the Mis.sitDiippi, 

 Appendix, p. 5(K)). It is very remarkable that these exi)erinH'nts and observations attracted no 

 more attention during the later discussions of the problem. 



The same principles explain the distribution on the floor, of the ocean of the liner materials 

 brouglit from the land. Notwithstanding the depth and extent of the oceanic currents, all the 

 solids materials brought to the sea are deposited near the land. All the recent observations show that 

 but little is carried far from shore; the profound depths of mid-ocean contain but little or none of 

 it, and we are all familiar with the clearness and intense blue of tlie waters therf. 



My exp(>rinients have extended to a considerable variety of salts, but more especially to the 

 chlorides, sulphates, and nitrates, to mixtures of these, and to organic substances, both colloids 

 and crystalloids, to carbhydrates and albuminoids, extracts of woods, herbs, and of peat, and 

 in a huge number of these, clearing was more rapid than in pure water. The effect of certain 

 neutral colloid organic substances, like the gums, is to favor suspension, as is well known. 



The action of some of the salts is obviously aided iu certain cases by the formation of i>er- 

 inanent chemical compounds. This is notably the case in the reaction of alum in certain-solutions 

 containing chlorid of calcium. 



The sparkling clearness of the natural waters of limestone regions is doubtless correlated 

 with the .solution of carbonate of lime, and the clearness of certain saline and alkaline waters has 

 often been remarked. So-called " alkaline" waters in the Far West are often discolored, particulai ly 

 with organic matter, but I have never seen them turbid with clay. * 



Any considerable quantity of suspended carbonate of lime in water also affects the deposition 

 of the clayey sediment, and calcareous delta deposits have special characters of their own. From 

 what I can learn, some of the phenomena of the Nile delta, the material of which is described as a 

 calcareous clay, are quite unlike those observed at the Mississippi delta, but my iuforniation is too 

 meager to venture more than mere mention here. 



The effect of sewage has also attracted attention. It has been claimed by a French writer 

 that some river waters have been made clearer and better adapted to certain manufacturing uses 

 by a slight sewage contamination. Numerous sanitary investigations have shown that waters 

 contaminated by sewage to a very dangerous degree are often of exceptional pellucidity and spark- 

 ling clearness. In experiments on a clayey garden soil from the Connecticut Valley, which 

 agitated with pure water retains the suspended matter with great tenacity, I found that minute 

 quantities of sewage soon rendered it as clear as the very clearest natural waters, while the pcn-tion 

 in pure water has a visible opalescence after six years' standing, the last three of which have been 

 in a dark, quiet closet. "The Broad street pump," famous iu sanitary literature, had great local 

 popularity because of the sparkling clearness of its waters. Well-to do people living miles away 

 sent their servants with jugs for it, as a choice drinking water, because of this clearness, until it 

 was closed l^y the authorities, after its sewage-contaminated waters had spread cholera into a 

 multitude of homes, several hundred dying iu a single mouth. 



1 think that where clay is precipitated by salts in the presence of organic matter which is 

 partly in solution and partly in suspension (as sewage), the clay carries down with it much of the 

 organic matter, probably in a sort of chemical combination similar to the "lake" formed by salts of 

 alumina with dye-stuffs in dj'eing. 



* Since the reading of this paper it has been reported to me from several sources that even horses and mules in 

 coHutrios witli alk.aline waters soon le.irn that niiiddied waters are not alkaline, and choose niiiddv water for drinkiii" 



