348 HOW CROPS FEED. 
The precipitate he operated with, contained (water-free) 
in 100 parts: 
SINGS scenes sn cnwe poi wee enn CER ee Re A eee BS KeRG BK ORM 49.0 
Pies die sca 11.1 
Oxide of Troms cscs . 21.9 
GAMES vissig seeeicigs acers.e oe . 69 
Masnesidveiisace trcaseue asia cate detects we “AL, 
Insoluble matters with traces of alkalies, etc.......... 10.0 
On digesting portions of this substance with solutions 
of sulphates of soda, potash, magnesia, ammonia, for a 
single hour, all the lime was displaced and replaced by 
potash—two-thirds of it by soda and nearly four-fifths of 
it by magnesia and ammonia. 
Further investigations by Rautenberg (Henneberg’s 
Jour. fiir Landwirthschaft, 1862, pp. 405-454), and 
Knop (Vs. St., VII, 57), which we have not space to re- 
count fully, have demonstrated that of the bodies possible 
to exist in the soil, those in the following list do not pos- 
sess the power of decomposing sulphates and nitrates of 
lime, potash, ammonia, etc., viz.: 
“i [ sed sand. ] 
aolinite (purified kaolin.) 
Carbonate of lime (chalk.) | These bodies have no absorptive effect, either 
[og (decayed wood.) f separately or together. 
Hydrated oxide of iron. 
Hydrated alumina. J 3 
Humate of lime, magnesia, and alumina, | Knop. 
Phosphate of alumina. 
Gelatinous silica. 
‘ 
Rautenberg 
dried in the air. 
These observers, together with Heiden (Jahresbericht 
uber Agriculturchemie, 1864, p. 17), made experiments on 
soils to which hydrated silicates of alumina, and soda, or 
of lime, etc., were added, and found their absorptive 
power thereby increased. 
Rautenberg and Heiden also found an obvious relation 
to subsist between the absorptive powers of a soil and cer- 
tain of its ingredients. Rautenberg observed that the ab- 
sorptive power of the nine soils he operated with was 
closely connected with the quantity of alumina and oa- 
