500 CHARLES A. DAVIS 



clamped into a vertical position and left perfectly still until the 

 marl had settled out, notes being made, daily at first, of the rate 

 of settling. In the beginning, the heavier particles settled 

 rapidly, forming, as does clay in settling from water with which 

 it is mixed, stratification planes, which, however, after a few days 

 disappeared, and only the lighter parts of the marl remained in 

 suspension. These were distinctly visible for five weeks, on 

 looking through the tube towards a window, and at the end of 

 six weeks, a black object lowered into the tube in a well-lighted 

 room, was not visible beyond ninety centimeters from the surface 

 of the water. (2) A glass cylinder with a foot, 38*^™ high and 'j^^ 

 wide, having a capacity of a little more than a liter was nearly 

 filled with distilled water and the residue from the washings of a 

 sample used in analysis was thoroughly mixed with it, and set 

 aside, notes being made as before. This material subsided rather 

 more slowly than the other, and at the end of ten weeks, under 

 daylight illumination, the bottom of the vessel was barely visible 

 when one looked down through the water from above. 



The results obtained by Barus^ in his work on the subsidence 

 of solid matter into suspension, in liquids, show that settling is 

 much more rapid in water containing dissolved salts, even small 

 proportion, than in distilled water, and the foregoing experi- 

 ments were checked as follows: (i) A cylinder about the size 

 of the one used in the second experiment was filled with water 

 in which a small amount of calcium chlorid had been dissolved, 

 and ammonium carbonate was added until a precipitate was 

 formed. This was stirred thoroughly and left to settle. In 

 three days the precipitate had fully subsided and the liquid was 

 clear. (2) Two cylinders of equal size were filled, one with 

 distilled water, the other with water from a river fed, in part, by 

 marl lakes. Equal quantities of fine marl were shaken up with 

 the water and the rate of settling was compared. The marl was 

 not as fine as that used in the other studies and settled more 

 rapidly. The river water was clear in fifteen days, while the 



^Carl Barus : "Subsidence of Fine Solid Particles in Liquids." Bull, of the 

 U. S. Geol. Surv., No. 36. 



