236 



THE IRRIGATION AGE. 



classification of soils given in agricultural chemistry, 

 although I question much if the use of the classifica- 

 tion originated through a study of that very useful 

 branch of science, but rather by absorption from our 

 friends the farmers. 



Agricultural chemistry informs us that soils carry- 

 ing from 75 to 100 per cent sand and to 25 per cent 

 clay is a sandy soil, and that sandy loams carry from 

 25 to 60 per cent clay and 40 to 75 per cent sand, 

 loamy soils 60 to 75 per cent clay and 25 to 40 per 

 cent sand, clay loams from 75 to 90 per cent clay and 

 10 to 25 per cent sand, and agricultural clay 90 to 100 

 per cent clay and to 10 per cent sand. 



This classification, while correct for the purposes 

 intended, and the farmer can tell to a nicety whether 

 corn will thrive on a sandy loam, or whether it requires 

 a clay soil, is misleading in the extreme as applied in 

 engineering. Take for example sandy loams which 

 have a range of 35 per cent. We find by one engineer 

 that he has constructed a canal through a sandy loam 

 which had only a velocity of 1^ feet per second and 

 yet eroded; while another informs us that he has run 

 water through sandy loams at a velocity of 2.75 feet 

 per second without erosion, while the average seems to 

 be 2% feet per second. 



As I have shown, and, no doubt, the practice of many 

 other engineers has shown them, the value of a soil 



for hydraulic purposes depends entirely upon the 

 proportions of sand and clay carried by that soil; that 

 being the case I contend that soils should be designated 

 by symbols representing those proportions; for ex- 

 ample, if a soil carries 80 per cent clay and 20 per 

 cent sand, it should be described as C. 80, S. 20 and 

 so on. 



The analysis of soils to determine these proportions 

 is very simple and may be performed in the office of any 

 engineer. The organic matter is first removed by burn- 

 ing in an open flame the soil which it is desired to test, 

 and the soluble salts are dissolved by placing the burnt 

 soil, stirring briskly, in a glass graduate filled with 

 water. The sand and clay will settle in the bottom of 

 the graduate in two stratse, the clay at the bottom and 

 the sand on top, the soluble salts remaining in sus- 

 pension. By the difference in color the sand and clay 

 are readily distinguishable and by the graduations on 

 the glass the proportions may be readily arrived at. 



The following table, based upon a series of experi- 

 ments from 1889 to 1893, and upon the foregoing theory, 

 may be of use and may explain some of the wide 

 differences of opinion as to the power of soils to re- 

 sist erosion by water. The value of clay for puddling 

 purposes has long been recognized and I contend that 

 it is equally applicable in the case of velocity. 

 (See Engineering News, Feb. 8. 1894, page 124.) 



TABLE SHOWING RESISTANCE OF SOILS TO EROSION. 



A RANCH ON THE LARAMIE K1VER IN WYOMING, NEAR ORIN JUNCTION. 



