GvrsuM. 331 



the former is incorporated with the indispensable manure, it is de- 

 composed, and carbonate of lime, ■« a state of minute division, and 

 for that reason easily absorbed, is ^he result. It is only upon tl)is 

 supposition that I can understand the elimination of the sulphuric 

 acid of the gypsum ; for if the lime really entered the vegetable in 

 the state of sulphate, the ashes ought to be much richer in that acid 

 than analysis shows. This same difficulty occurs in the hypothesis 

 of Liebig. If the 56 lbs. of ammonia derived from the atmosphere 

 penetrated the plant in the form of sulphate, there must enter at the 

 same time 130 lbs. of sulphuric acid, and which ought to be recover- 

 ed in the ashes of the crop from one acre. Now, the ashes of 41 

 cwts. of gypsed clover, abstracting the carbonic acid, weigh 2 cwts. 

 8 lbs., containing in the 100, 3^ of sulphuric acid. But the amount 

 of ash, were the acid of the ammoniacal sulphate fixed in the crop, 

 would rise to 3 cwt. 1 qr. 20 lbs., and the ash would then contain 

 70 per cent, of sulphuric acid. 



Before promulgating this last objection against received theories, I 

 thought it right to ascertain whether the ashes contain, in the state 

 of sulphate, the whole of the sulphur pre-existing in the incinerated 

 plant. For it w^as not impossible that at the high temperature em- 

 ployed, the silica might react upon the sulphates so as to expel a 

 portion of the sulphuric acid. However improbable this expulsion, 

 owing to the great excess of potash always present in clover ash, 

 it seemed expedient to determine the fact. 



After having made out as exactly as possible the quantity of ash 

 left by the hay, and also the sulphuric acid, I took a certain weight 

 of the same hay, burned it in a platina crucible along with a mixture 

 of chlorate and carbonate of potash, and then sought for the sulphu- 

 ric acid in the product of the ignition. 



1000 parts of the plant furnished directly 3 of sulphuric acid, and 

 by analysis of the ash, 2.8. 



Thus, the alkaline ashes retain all the sulphur pre-existing in the 

 plant which produced them. 



I have laid stress upon the small proportion of sulphuric acid in a 

 crop of clover, because there yet remains for consideration a third 

 theory of gypsing, which I have helped to propagate, although 

 doubtful concerning the author. This is founded upon the assumption 

 that the proportion of sulphur is much greater in the leguminous 

 than in the cereal tribe. Now, as gypsum is generally adapted to 

 the manurement of leguminous plants, the origin of the sulphur has 

 been ascribed to sulphate of lime incorporated with the soil. This 

 view appeared the more plausible to M. Dumas and myself, inas- 

 much as in accordance with it plants operat^-d as reducing agents. 

 It is, besides, very probable that sulphur, as an immediate constituen 

 principle of vegetables, is derived from sulphates ; but do leguminous 

 plants really contain more than the cereals ? This seems doubtful 

 since careful investigation of the azotized principles of plants has 

 shown gluten, caseine, and legumine to be nearly identical in com- 

 position. I moreover find upon analysis of the ashes, that clover 

 haricots, and beans do not sensibly contain naore sulphur than rye, 



