471 



tity of nitrogen), affording only 11.95 parts of gluten, and 64.34 parts 

 of amylin or starch ; whilst the same quantity, grown on a soil man- 

 ured with human urine, yielded the maximum of gluten, namely, 35.1 

 per cent. Putrified urine contains nitrogen in the forms of carbonate, 

 phosphate, and lactate of ammonia ; and in no other form than that of 

 ammoniacal salts." — p. 136. 



As illustrative of the value of ammonia in vegetation, Liebig refers 

 to guano. This is the excrement of sea-birds, and found in large 

 quantities on several islands in the South Sea. The effect of this man- 

 ure is understood to be most powerful. It renders the soils, which 

 consist of clay and sand, and contain, as is represented, no organic 

 matter, highly fertile. This manure is composed principally of salts of 

 ammonia, and a few earthy salts. 



Liebig, if his theory be well founded, has solved the secrets of the 

 operation of gypsum. Jt has been supposed, that gypsum acted upon 

 plants as a stimulus, or like ardent spirits upon animals. But plants 

 are not animals. They have no nerves, which may be tightly drawn 

 or relaxed ; and such suppositions, which serve only to betray our ig- 

 norance, are without foundation. No substance can cause the leaves 

 of plants to appropriate an excess of carbon from the atmosphere, 

 when the oiher constituents of the plants are wanting. The influence of 

 gypsum is to fix the ammonia which is brought into the soil, and pre- 

 venting its evaporation, give it out as the plants may receive it. This 

 effect is produced by the double decomposition of the carbonate of am- 

 monia, and of the gypsum or sulphate of lime, by which sulphate of 

 ammonia and carbonate of lime are formed. His notions on this sub- 

 ject, being the first satisfactory attempt at a solution of the mystery al- 

 ways connected with the application of this extraordinary substance, are 

 curious and interesting. 



" In order," he says, " to form a conception of the effect of gypsum, 

 it may be sufficient to remark, that 100 lbs. Hessian of burned gypsum 

 fixes as much ammonia in the soil as 6,250 lbs. of horses' urine would 

 yield to it, even on the supposition that all the nitrogen of the urea and 

 hippuric acid were absorbed by the plants without the smallest loss, in 

 the form of carbonate of ammonia." — p. 143. 



He is equally original in his explanation of several other facts. 



" The advantage of manuring fields v/ith burned clay and the fertility 

 of ferruginous soils, which have been considered as facts so incompre- 

 hensible, may be explained in an equally simple manner. The oxides of 



