. 
. 
: 
E. W. Hilgard—WSilt analysis of Soils and Clays. 289 
make an equally material difference whether or not the impal- 
pable matter usually classed as “clay” were really, in the main, 
silicate of alumina, or simply silex, or other mineral powder. 
Equally important are, of course, the corresponding differ- 
ences in the properties of clays intended for use in the arts. 
In the prosecution of my researches on the soils of the State 
of Mississippi, I found myself confronted by these difficulties, 
and by the necessity of providing for some mode of operation, 
and means of designating the several physical constituents of 
soils, which should not only insure more accurate results, but 
should also render these capable of ready comparison all the 
world over. 
I need not recapitulate the often-discussed objections to 
Nobel’s apparatus, with its four vessels of oe capacity 
and slope of sides, and variable head of pressure. Not one of 
the five sediments obtainable by its use is ever of a character 
approaching uniformity ; and even in one and the same instru- 
ment, successive analyses of one and the same material differ 
widely in their results. 
Schultze’s elutriating apparatus, as modified and used by Fre- 
senius in his investigations of the clays of Nassau—a tall, 
conical champagne glass, with an adjustable stream of water 
descending through a tube in the axis—answers a better pur- 
pose; but offers the inconvenience of the accumulation of 
heavy sediments around the mouth of the tube, whereby not 
only the velocity of the stream is changed, but its failure, at 
low velocities, to agitate the whole mass of the substance under 
treatment, allows portions of the latter to escape the elutriating 
action altogether. And since in soil analysis special impor- 
tance attaches to these finer sediments, which are carried off at 
low velocities, this objection is a capital one. 
ntending to carry out in a convenient form the idea (already 
en : 
“hydraulic value,” I adopted in place of a variable head of 
Water, a constant one (a Marivctte’s-bottle arrangement, adapted 
to ten-gallon carboys), modifiable by means of a stopcock 
with a long lever moving on a graduated arc, on which the 
Positions corresponding to given velocities in vessels of known 
‘ross-section of mouth, are marked off according to empirical 
determinations, 
as order to obviate the inconvenience arising from the aceu- 
Tulation of sediment around the orifice of the tube delivering 
€ current, I introduced an intermediate conical relay reser- 
vor (R, fig. 2; a test glass, cut short) at the point of the 
* For | see Plate I. 
Am. Jour, Sc1.—Tuirp —_— ecggen No. 34 —Ocr., 1873. 
