CHEMICAL ANALYSIS OF SOILS. 199 



soil, which has passed through the finer sieve, just up to the 

 point at which paper becomes brown, but not sufficiently to 

 scorch it. Weigh out 100 grains of the baked soil, as above, 

 and boil it for half an hour, in a solution of .50 grains of sale- 

 ratus, or carbonate of potassa,* dissolved in 4 oz. of water. 

 When it has settled, the clear liquor may be poured off, and 

 the residue washed in 4 oz. of boiling water. 



The whole is now to be thrown upon a filter, which should 

 be previously dried at the same temperature with the baked 

 soil, and carefully weighed. Wash the soil upon the filter 

 until the water passes through colorless. If carbonate of am- 

 monia is used, instead of washing the soil, it should be di- 

 gested with the same quantity of the solution, at least twice, 

 and then washed until there is no alkaline reaction in the 

 water as it passes the filter. Mix all these liquors together, 

 and they will form a brown-colored solution containing all the 

 soluble geine. The sulphates have been converted into car- 

 bonates, which, with the phosphates, are on the filter with the 

 soil. Dry the filter, raising the heat gradually to above that 

 of boiling water, and then weigh the contents. The loss is 

 the quantity of soluble gcine. Note this also, and mark the 

 filter 2. 



3. To test the accuracy of the analysis thus far, precipitate 

 the geine from the alkaline solution, with excess of lime-wa- 

 ter. The geine will combine with the lime, forming the ge- 

 ate of lime, and when a sufficient quantity of lime-water has 

 been added, the liquor will be colorless. Throw the whole 

 upon a weighed filter, and wash with a little acetic, or very 

 dilute hydrochloric acid, and this will combine with the 

 lime, and pass through the filter, leaving the geine quite pure. 

 Dry and weigh as before. If this quantity corresponds with 



* Dr. C. T. Jackson objects to carbonate of potassa, because it is 

 impoissible to wash out the last traces of it from the vegetable fibre, 

 and because the subcarbonate of potassa takes up a portion of the alu- 

 mina. 



