Page:The Formation of Vegetable Mould through the Action of Worms (1881).djvu/256

 carbonate of lime and on the oxides of iron. It is, also, known that some of these acids, which were called long ago by Thénard azo-humic, are enabled to dissolve colloid silica in proportion to the nitrogen which they contain. In the formation of these latter acids worms probably afford some aid, for Dr. H. Johnson informs me that by Nessler's test he found 0.018 per cent. of ammonia in their castings.

The several humus-acids, which appear, as we have just seen, to he generated within the bodies of worms during the digestive process, and their acid salts, play a highly important part, according to the recent observations of Mr. Julien, in the disintegration of various kinds of rocks. It has long been known that the carbonic acid, and no doubt nitric and nitrous acids, which are present in rain-water, act in like manner. There is, also, a great excess of carbonic acid in all soils, especially in rich soils, and this is dissolved by the water