830 GYPSUM. 



or even three times the quantity of these substances which those 

 grown previously to the gypsing contained. Representing, for ex- 

 ample, by unity the quantity of the several bases and acids of the 

 crop grown without gypsum, we should have the quantities of the 

 same principles contained in the crops produced upon the gypsed 

 soils represented by the following numbers : 



Phosphoric Sulphuric Mag-nesia and Potash and 



Chlorine. aciJ. aoid. Lime. metallic oxide. ioda. Silica. 



1841 2.2 2.2 2.1 2.5 2-1 3.5 1.0 



1842 2.8 3-3 3-1 3-1 3.7 3.2 1.0 



Silica appears to form the onl}' exception here, which would lead 

 us to conclude that this earth was only absorbed by clover in the first 

 period of its growth. Potash and lime are the bases which enter in 

 largest proportion into the mineral constitution of clover ; and there 

 is another fact made evident which deserves particularly to fix at- 

 tention : it is that the lime assimilated subsequently to the gypsing, 

 bears no kind of relation to the quantity of sulphuric acid fixed dur- 

 ing the same space of time. The excess of acid and of lime obtain- 

 ed from the ash of the gypsed clover over that of the ungypsed, is 

 for: 



1841, Sulphuric acid 4-8 Lime 47.2 



1842, " 6.0 '• 70.6 



Supposing further, that the sulphuric acid assimilated subsequently 

 to the gypsing was taken up in the state of sulphate of lime, we find 

 that : 



In 1841 the ^psed crop absorbed 18 lbs. of this salt. 

 In 1842 " 22 lbs. 



These quantities are so small as to lead us to suppose that the 

 utility of gypsing consists in furnishing the plant with the large pro- 

 portion of lime which it seems to require. Gypsing would then be 

 equivalent to the application of lime ; and in fact, according to 

 Schwertz, Paris plaster is replaced in Flanders by slaked lime, by 

 the lye-washed ashes of wood, and by peat-ash, witii decided advan- 

 tage.* Some peat-ash contains sulpliate of lime, others none at all. 

 What is employed successfully, most likely presents sulphuric acid 

 in the state of an alkaline sulphate. 



Wood-ash, which is certainly the best manure for artificial mead- 

 ows, may contain upon an average one per cent, of sulphuric acid, 

 and when lye-washed, the proportion ought to be much less; if per- 

 fectly washed, it ought to be null ; at all events, there is no sulphate 

 of lime present to fix the ammonia of the rain-water. Independently 

 of earthy phosphates, so useful to all plants, lye-washed ashes fre- 

 quently yield more than 80 per cent, of chalk. We thus perceive, 

 in a general way, that the manures which stimulate the vegetation 

 of clover are always calcareous, the lime being either in the slate 

 of sulphate or carbonate, which exists abundantly in the crops, com- 

 bined with organic acids, and tVeed consequently of nearly the whole 

 of the inorganic acid with which it was originally associated. As- 

 suiwig that gypsum acts like chalk, it may be conceived that when 



* Schwertz, Culture dcs Plantes fourrageres, p 7? 



