ON THE SOURCE OF SULPHUR. 



one equivalent of nitrogen. Hence it is necessary that the car- 

 bon of six equivalents of carbonic acid must at the same time be 

 taken up, and enter into combination with the nitrogen, in order 

 to produce the principal nitrogenous constituents which contain 

 one equivalent of nitrogen to eight equivalents of carbon. 



The passage of sulphur derived from a sulphate into the com- 

 position of vegetable matter, necessarily indicates that the sul- 

 phate has been exposed to the action of the same causes as those 

 by which the decomposition of carbonic acid was effected in the 

 plant ; and, therefore, that the sulphuric acid has been decom- 

 posed into sulphur and oxygen, the former of which is assimi- 

 lated, whilst the latter is separated. If we suppose the sulphuric 

 acid to be presented in the form of sulphate of potash or soda, the 

 bases of these salts must be set at liberty after the decomposition 

 of their acid. 



Now we actually find these bases in all cultivated, and even 

 in most wild plants. They are found either united to organic 

 acids, or, what is still more remarkable, they are found in union 

 with the vegetable compounds containing sulphur. The vege- 

 table casein of peas, beans, and other leguminous plants, is itself 

 insoluble in water; but it is very soluble in the form in which 

 it occurs in the plant. This solubility is due to the soda and 

 potash with which it is united. In like manner, the albumen 

 contained in the juices of plants is combined with an alkali ; and 

 we must suppose that vegetable fibrin, the insoluble ingredient of 

 cereal plants, must have originally been soluble, and have at- 

 tained its position in the seeds by the agency of alkalies. 



The potash and soda of the alkaline sulphates which furnish to 

 plants their sulphur, remain, therefore, either in combination 

 with the ingredients containing that element, or they enter into 

 some new state of combination, or, finally, they are returned to 

 the soil. 



Gypsum (sulphate of lime) is the most generally diffused sul- 

 phate. Being soluble, it may either pass directly into the plant, 

 or it may be decomposed by the carbonate of ammonia existing 

 in rain-water, when its sulphur will pass into the plant in the 

 form of sulphate of ammonia. 



A solution of gypsum containing common salt or chloride 



