MECHANICAL ANALYSIS OF SOILS. 197 



and agitate it for a while in a given measure of water, pour 

 off the suspended matter upon a filter.* This will consist 

 mostly of vegetable substances, clay and fine sand. By ex- 

 amining the residue in the glass jar, the larger particles of 

 the mineral ingredients can easily be detected. Put the con- 

 tents of this jar on the other filter, and after the water has pas- 

 sed out, the filters with their contents may be weighed, and the 

 relative proportions determined. If the filter contain free acid, 

 little lime water will cause a white precipitate, which is either a 

 sulphuric or carbonic acid ; if the latter, the precipitate will 

 effervesce with sulphuric acid, and will be converted in- 

 to gypsum, or sulphate of lime. To ascertain whether there 

 is any sulphate of iron or copperas, pour into the liquor a 

 few drops of the infusion of gall-nuts, and it will give a dark 

 or brown color. 



To test for oxide of iron, wash the filter, containing the 

 clay and fine particles, with diluted muriatic acid, and apply 

 the infusion of galls ; and if it becomes black, it contains 

 iron. 



The above process can be easily performed, and some val- 

 uable knowledge obtained. It may be known, for example, 

 whether the soil is mostly silica or alumina, or whether it 

 contains free acid, like the sulphuric, or whether the acid is 

 combined with oxide of iron, a substance very injurious to 

 vegetation ; but which is, by the application of lime to de- 

 compose the copperas, easily converted into gypsum (sul- 

 phate of lime), a valuable manure. The above method, how- 

 ever, cannot be depended upon where accuracy is required, 

 and we will now proceed to describe a method of analysis 

 which is very simple, and which some farmers may be able 

 •to adopt. It is substantially the method of Dr. Samuel L. 

 Dana, of Lowell, Mass. 



* The filters may be made of fine linen cloth, of equal weights,. 

 placed in a common glass tunnel, and lined witii unsized paper. 

 17 



