E. W. Hilgard—Silt analysis of Soils and Clays. 335 
compound articles which had resisted the boiling process. 
Besides, downward currents on the sides of the vessel will 
form, despite all precautions; so that the interior surface of 
the cylinder becomes coated with pendant flakes of coalesced 
sediment. These must from time to time be remove 
means of a feather, so as to again bring them under the influ- 
ence of the stirrer; but it is, of course, almost mathematically 
impossible that under these circumstances, any of the sediments 
subject to coalescence should ever become completely ex- 
hausted. Practically, the degree of accuracy attainable at best, 
renders it unnecessary to continue the operation beyond the 
point when only a fraction of a milligram of sediment comes 
over with each liter of water. It is admissible, and even desir- 
able, to run off rapidly the upper 3 of the column at inter- 
vals of 15 to 20 minutes; whereby not only time is gained, but 
also the sediment in the reservoir is stirred and brought under 
the influence of the churner, for more complete disintegration. 
It is noticeable that recent sediments—river alluvium, ete.— 
are much more easily worked than more ancient ones ; as might 
be expected. 
_ Up to 4™™ hydraulic value, the use of the rotary stirrer is 
indispensable, on account of the tendency to the formation 
of compound particles. Beyond, this tendency measurably dis- 
appears, so that for the 
rse Sediments of 8 to 64™™, hydraulic stirring may be em- 
ployed, and an elutriating tube of smaller diameter may advan- 
tageously be substituted, in order to diminish the otherwise 
Somewhat extravagant expenditure of water. The entire 
amount required for one analysis is from 25 to 80 gallons; pro- 
vided a thorough previous disintegration has been secured. 
The average times required are as follows: 
eduheHy Re ta ora5mm 80 to 40° 
OO eg el. ore oe O-5@™ 15 to 25 
Oh. Ver ie eh ee ieee 1 5 to 10° 
Otay guy acres et aie od 2 to 6472 6 to 10° 
Total, 56 to 85" 
With p 
matically, at night; completing an analysis (except the clay and 
finest sift determinations) in the course of three or four day 
i 
the <0-25 sediment, which, moreover, is so diffusible in water 
that it cannot readily be collected on a filter. I find it best, 
* A somewhat 1 : igh ° for 5-6 days. But 
clayey soil will continue to lose weight at 100°, for 5 hae 
atter the first 6 hours the loss becomes insignificant for the purpose in question. 
