244 DISINTEGKATION Chap. V. 



carbonate of lime and on the oxides of iron. 

 It is also known that some of these acids, 

 which were called lon^ ago by Thenard 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. 

 It may be here added that I have recently 

 been informed by Dr. Gilbert "that several 

 " square yards on his lawn were swept clean, 

 " and after two or three weeks all the worm- 

 w castings on the space 1 were collected and 

 " dried. These were found to contain 0*35 

 " of nitrogen. This is from two to three times 

 " as much as we find in our ordinary arable 

 " surface-soil ; more than in our ordinary 

 " pasture surface-soil ; but less than in rich 

 " kitchen-garden mould. Supposing a quantity 

 " of castings equal to 10 tons in the dry 



* A. A. Julieii " On the Geological action of the Humus-acids," 

 ' Proc. American Assoc. Science,' vol. xxviii., 1879, p. 311. 

 Also on " Chemical erosion on Mountain Summits ;" ' New York 

 Academy of Sciences,' Oct. 14, 1878, as quoted in the ' American 

 Naturalist.' See also, on this subject, S. W. Johnson, ' How 

 Crops Feed,' 1870, p. 138. 



