172 MEMOIIIS OF TDE NATIONAL ACADEMY OF SCIENCES. 



The water stored iu reservoirs lor the supply of cities sometimes in summer becomes 

 offensive to the taste and smell, the cause being usually referred to the solution and decay of 

 organic matter in the source of supply, or the growth and decay of low organisms in the 

 reservoirs and distributing pipes. In New Haven, where I have carefully watched the phenomena 

 in connection with the tenii)erature and clearness of the water, on several occasions when such 

 smell and taste was occurring heavy .summer storms have roiled the waters, and each time this 

 has taken i>la(:e the special smell and taste have disappeared with the advent and precipitation of 

 the suspended mud. 



Water containing a very small proportion of organic albuminoid will putrefy and stink, and if 

 this be mixed with sea-water or brackish water it becomes much more offensive to the smell than 

 in fresh water, and there is an evolution of sulphureted hydrogen along with that of the putrid 

 organic gases. I have experimented with dilute solutions of the albuminoids dissolved from marsh 

 vegetation and from wood. If such dilute solution be mixed during the putrefactive stage with 

 roiled water, a new set of phenomena occurs, and a considerable of the organic matter goes down 

 with the clay as it subsides. I have not followed this up with satisfactory examinations of the 

 precipitate, but some of the samples have strongly the odor of the offensive "blue mud" in the 

 shallow harbors of our seaport towns. The sanitary bearings of this I alluded to in a paper a few 

 years ago, but the facts have doubtless also their geological signiticance, and probably have some- 

 thing to do with the "mud-lump" phenomena at the mouth of the Mississippi. The occurrence of 

 these " mud lumps "only in shoal salt or brackish water, and never in the fresh water swamps, and 

 the evolution of organic gases and of sulphureted hydrogen, are at least suggestive, and other phe- 

 nomena relating to them are in accordance with some of the observations made in the experiments 

 on the mutual reactions of decaying organic matter, brackish water, and" suspended clay. 



The effect of the common mineral acids on suspended clays is even more rapid than that of 

 the salts. Some turbid waters are cleared more in five or ten minutes by the addition of sul- 

 phuric, nitric, or chlorohydric acids, or, better, mixtures of these, than in as many weeks or even 

 months in pure water. 



A considerable number of experiments have been made with acid similar to those described 

 with salt by beginning with a stronger solution and reducing its strength when the material had 

 settled, by decanting the clear portions, and adding an equal volume of distilled water. I may 

 say here that the most of these experiments have been conducted iu precipitating flasks made for 

 the purpose, of hard glass, about a foot high, three inches in diameter at the base and one at the 

 top. In some cases the whole of a portion of clay was treated; in others, after a watery suspension 

 had stood several days, and when all the coarser particles had subsided, the upper part would be 

 decanted, thoroughly mixed to insure uniformity, then divided into several portions for treatment 

 in different ways for comi)arison with each other. 



With those treatei with acids the usual course has been to begin with clay in an acid or 

 mixture of acids of known strength, amounting to 20 to 60 per cent, of the whole volume of the 

 tluid under experiment, allowing it to settle, decant a given amount of the clear portion, and add 

 the same amount of distilled water, the strength of the acid in the successive dilutions being- 

 calculated and the successive dilutions recorded. 



With the mineral acids it has been tne rule that at first the flocculation and precipitation are 

 very rapid, the rapidity but slightly diminishing with great reductions of strength until the propor- 

 tion of acid became very small; then there would be a marked increase in time needed, then finally 

 and suddeidy the subsiding would be as slow or slower than in pure water. One of the specimens 

 exhibited to the Academy is of a fine clay from Hartford, Conn. I began with 60 per cent, nitro- 



