213 



by the two latter methods, it has been approximately esti- 

 mated for a series of specimens too numerous to be subjected 

 to the more operose process of analysis, by ascertaining by the 

 first mode the amount of the green mineral, and then calculating, 

 from the average per-centage of potash, the proportion in which 

 it prevails in the particular marl. 



Though it is not presumed that among those engaged in agri- 

 culture, more than a very few persons possess the requisite 

 chemical skill, or the facilities for this species of research, yet 

 for the sake of such as may chance to be competent to execute 

 this kind of analysis, I have thought it well to introduce a state- 

 ment of the method of analyzing the mineral in question. Several 

 plans, modifications of the same general method, have been tried 

 for the purpose of arriving, if possible, at some mode sufficiently 

 simple to make it practicable by those who possess but a limited 

 knowledge of analytical chemistry. But the nature of the com- 

 pound seems not to admit of either a very direct or expeditious 



mode of operation. 



) 



Method of analyzing the Greensand. 



1. Digest the mass in a flask with pretty strong muriatic acid, 

 by a sandbath heat for at least three days, or boil it actively for 

 five or six hours. Every thing is dissolved but the silica, which 

 must be filtered, ignited, and weighed. 



2. Precipitate the oxide of iron and alumina by ammonia and 

 estimate them together, and detach the alumina by caustic potash. 



3. Evaporate the ammoniacal solution to total dryness, and 

 heat the mass to incipient redness, to expel the muriate of ammo- 

 nia. There remain the chlorides of calcium, magnesium, and 

 potassium, which redissolve in water, dividing the liquor. 



4. To one half add oxalate of ammonia, and separate the lime, 

 then by ammonia and phosphate of soda separate the magnesia. 

 Subtract the combined weight of these two computed as chlo- 

 rides, from the original triple chloride, and we have the chloride 

 of -potassium. 



5. Now evaporate the other half again to dryness, and dissolve 

 up all the chlorides of calcium and magnesium by alcohol, and 

 dry and weigh the residual chloride of potassium. If further 



