188 HK. W. Hilgard— Objects and Interpretation of Soil Analyses 
caused investigations to be made by Dr. R. H. Loughridge 
(this Journal, Jan., 1874, p. 20), on a subsoil selected for its rep- 
resentative position and derivation—a drift soil covering, prob- 
ably, some 15,000 square miles in the uplands of Western Ten- 
nessee and Mississippi, and perhaps as fully “ generalized ” in 
its origin as can be obtained. The result of this investigation 
was that hydrochloric acid of about the specific gravity of 1:11 
seems to exert the maximum effect, and that the extraction is 
practically complete after a water-bath digestion of five days. 
These conditions of digestion have been substantially main- 
tained in all the investigations made under my direction. An 
excess of time of digestion results simply in higher percentages 
of alumina and soluble silica, or what is equivalent, in a far- 
ther decomposition of kaolinite particles. 
The methods of analysis used by me are substantially those 
given in the first Kentucky Report, volume I, by Dr. Robert 
Peter, with such changes as the progress of analytical chemistry 
suggested. All the reagents have been especially prepared, 
or purified, in the laboratory itself; porcelain beakers only have 
been used in the digestions ; and generally every possible pre- 
caution has been taken to insure correctness in the determina- 
tion of the minute percentages of the important ingredients. 
Numerous repetitions have, in most cases, confirmed the cor- 
rectness of the work. 
Of other determinations, the one preceding all analytical 
operations has been the determination of the “ moisture-coefhi- 
cient ” of the “ fine-earth,” by exposing a very thin layer of the 
same to a fully saturated aiziephere for at least twelve hours, 
at a sensibly constant temperature. As previously stated, [ 
have in these determinations come to results differing material- 
ly from those obtained by Knop, Schiibler, and others ; prob- 
ably because of the more complete fulfillment of the conditions 
of full saturation of air as well as soil. I find that for most 
soils, the absorption-coefficient is practically constant at tem- 
peratures between +7° and +25° C.; and contrary to the con- 
clusions reached by Adolph Mayer. 
find that this coefficient exerts an exceedingly obvious and 
important influence upon the actual productiveness of soils. 
An investigation reaching beyond the temperature-limits men- 
tioned, and also embracing the use of a partially saturated 
atmosphere, has just been made in my laboratory and will short- 
ly be published. : 
A determination of the total “ volatile matter” of the soil, 
that is, its organic matter and combined water, by ignition, 1S 
made on the portion of soil used for the determination of phos- 
phoric acid by means of molybdic acid. While this determin 
ation is necessary to the “summing up ” of the analytical state- 
