Note 11 — Chapter III · SOIL ANALYSIS AND THE HISTORICAL METHODS OF SOIL INVESTIGATION.

The classic experiments of Sachs, in producing etchings on marble slabs, and the etchings observed occasionally on rock surfaces are the proofs universally cited. The experiments of Czapek, who substituted slabs of aluminum phosphate and other substances for the marble, and those of Kossowitch, show that the action can be accounted for more satisfactorily and reasonably as due to dissolved carbon dioxide. In fact such etchings can be produced on marble slabs by laying platinum wires upon them and covering with moist soil, or cotton, or mats of filter-paper; see Bull. No. 22, p. 14, and Bull. No. 30, p. 41, Bureau of Soils, U. S. Dept. Agriculture.