BULLETIN OF THE BUSSEY INSTITUTION. 347 
this particular field. Carbonate of potash would naturally soon be 
washed out of the soil almost anywhere, or decomposed by react- 
ing chemically on matters in the earth. In all probability the com- 
pacting effect is produced immediately on the addition of the car- 
bonate, or soon afterward, and it is manifestly something which 
endures long after-the carbonate of potash has ceased to exist in 
the soil as such. There is an old remark of Sir Humphrey Davy * 
which is not inconsistent with the facts and views here presented. 
He says: ‘* The general tendency of the alkalies is to give solubil- 
ity to vegetable matters. . . . The vegetable alkali (potash) like- 
wise has a strong attraction for water, and even in small quantities 
may tend to give a due degree of moisture to the soils or to ma- 
nures; though this operation, from the small quantities used or 
existing in the soil, can be only of a secondary kind.” It is not 
impossible that Davy may have been told by some of his agricul- 
tural acquaintances of the fact that wood-ashes tend to keep land 
moist. 
The significance of the agglutinative power of the alkaline car- 
bonates, and the danger of employing them in improper situations, 
may be still further illustrated by considering their action upon 
clay. It is a known fact that alkaline lyes added to clays tend to 
‘* puddle” them,t —?7. e. to make them even more sticky, adhe- 
sive, and impermeable than kneading with mere water would ; while | 
lime, as well as salts of lime and various other saline compounds, 
act in a contrary sense to diminish the adhesiveness. It is said 
that clay which has beer kneaded with saleratus-water will ‘‘ set” 
with peculiar firmness on drying. ‘This peculiarity is sometimes 
put to practical use in domestic economy, as when mixtures of 
sifted wood-ashes and clay stirred up with a little water are used 
as a cement for stopping cracks in stoves and holes in stove-pipes. 
The common remark of our farmers that wood-ashes are excellent 
on gravelly or sandy soils would naturally suggest the inference 
that experience has taught them not to employ such ashes on stiff 
clays. | 
B. — Carbonate of potash (wood-ashes) favors the decay of humus 
(or other orgunic matter) in the soil in such wise that the nitrogen 
of the humus is made fit for the support of plants. 
I have already discussed this property of the potassic carbonate 
* ‘*Blements of Agricultural Chemistry,” p. 229 of the Philadelphia edi- 
tion of 1821. 
+ Hilgard, ‘‘ Pacific Rural Press,” 1878, 15. 130. 
