C 139 ] 



appears to be composed of one proportion of mangan- 

 esum 113, and three of oxygene 45. It is distinguish- 

 ed from the other substances found in soils, by its pro- 

 perty of decomposing muriatic acid, and converting it 

 into chlorine. 



7. Vegetable and animal matters are known by their 

 sensible qualities, and by their property of being de- 

 composed by heat. Their characters may be learnt 

 from the details in the last Lecture. 



8. The saline compounds found in soils, are com- 

 mon- salt, sulphate of magnesia, sometimes sulphate of , 

 iron, nitrates of lime and of magnesia, sulphate of po- 

 tassa, and carbonates of potassa and soda. To des- 

 cribe their characters minutely will be unnecessary; the 

 tests, for most of them have been noticed p. 103. 



The silica in soils is usually combined with alumi- 

 na and oxide of iron, or with alumina, lime, magnesia, 

 and oxide of iron, forming gravel and sand of differ- 

 ent degrees of fineness. The carbonate of lime is 

 usually in an impalpable form, but sometimes in the 

 state of calcareous sand. The magnesia, if not com- 

 bined in the gravel and sand of soil, is in a fine pow- 

 der united to carbonic acid. The impalpable part of 

 the soil, which is usually called clay or loam, consists 

 of silica, alumina, lime, and magnesia; and is, in fact, 

 usually of the same composition as the hard sand, but 

 more finely divided. The vegetable or animal, mat- 

 ters, (and the first is by far the most common in soils) 

 exist in different states of decomposition. They are 

 sometimes fibrous, sometimes entirely broken down 

 and mixed with the soil, 



