280 APPENDIX TO PART I. 



loss, would seem to be, not to wait for the slower action 

 of carbonic acid upon it, but to combine it directly with 

 those acids, which form with it salts fixed at common tem- 

 peratures. 



*' Hence, Liebig advises the addition of sulphuric or of 

 muriatic acid, both cheap substances, to the other materials 

 of the dung-heap, which, forming with the ammonia pres- 

 ent, the sulphates and muriates of that alkali, would at 

 once prevent any loss of it by evaporation. 



*' If these expedients be not adopted, it should at least be 

 borne in mind, that unless means are taken to prevent it,, 

 the most valuable portion of the manure is constantly 

 escaping, during exposure to air and sun, by evaporation, 

 and also by draining off into the ground, whence, instead 

 of a material calculated to afford a ready supply of nitro- 

 gen to the plant, we obtain an effete mass, in which that 

 element is in a great measure wanting, and which, there- 

 fore, can only influence the growth of plants, by virtue of 

 the phosphoric salts and other fixed ingredients still pres- 

 ent in it. 



*' These views also throw some new light upon the use 

 of gypsum, or sulphate of lime, as a manure to certain 

 crops. 



*' The fact, that leguminous plants contain this substance 

 as an essential ingredient, may in some measure explain 

 its fertilizing effect on them, but it is also found serviceable 

 to turnips and cabbages, which do not appear to contain it, 

 nor does it seem easy thus to explain the superior advan- 

 tage said to arise, from scattering it in fine powder over 

 the leaves of clover and saintfoin, as is practised in France 

 and in North America, and with such manifest good effect, 

 that, it is said, if the substance be partially applied to a 

 field, the portions that have received this dressing may 

 afterwards be distinguished from the rest by the superior 

 luxuriance of the crop. 



''Liebig, therefore, has suggested another mode in 

 which gypsum may be beneficial to crops in general, by 

 reference to the property which it possesses, of depriving 

 ammonia of its volatility, and thus preventing its escape 

 into the atmosphere. 



''This effect arises from the double decomposition which 

 takes place, when sulphate of lime and carbonate of ammo- 

 nia are brought together, the lime being converted into a 

 carbonate, and the ammonia uniting with sulphuric acid. 



' ' The above theory of its use being admitted, we may 



