1^4 



CHYMISTRY APPLIED TO AGRICULTURE. 



nated, and they are left to dry : a pit four feet square and 

 three feet deep is dug in the earth ; this is heated with 

 split wood, and the saline plants are afterwards thrown 

 gradually in : combustion is continued during seven or 

 eight days ; the ashes become fused in the pit, and remain 

 in this state till the end of the process : when the combus- 

 tion is completed y the whole is allowed to cool, and then 

 the block of soda ie divided into large pieces for the market. 



I have always observed that when this mass of soda 

 bubbles up in the pit, there escape from the surface jets 

 of flame which appear to arise entirely from the combus- 

 tion of sodium ; the perfect resemblance which the flame 

 bears to that of the burning metal, struck me very forci- 

 bly when I saw sodium burned for the first time. 



The plants which are most commonly burned for ob- 

 taining soda, upon the borders of the Mediterranean and 

 of the ocean, are the salicornia europea, the salsola tragus ^ 

 the statice Jimonium, the triplex portulacoides, the salsola 

 kali, the icareck, &c. The soda which is aflTorded by some 

 of these is of a middling quality : the richest in alkali is 

 the salicornia ; in some of them it does not exist sensibly ; 

 these abound in muriate and sulphate of soda mixed and 

 strongly (frittes) fused with lime, silica, alumina, and 

 magnesia ; the soda extracted from these plants, though 

 weak, has nevertheless its use in the arts ; it is employed 

 in glass works, where, by means of the lime it contains, 

 and the charcoal which is made to enter into the composi- 

 tion for making glass, the sulphate of soda is decomposed, 

 and the salt being left free promotes the fusion of the 

 earthy substances. When soda contains 10 or 12 per cent. 

 of alkali, it serves to make weak leys in the soap manufac- 

 tories. 



In addition to the so(ia procured by the combustion of 

 marine plants, chymistry furnishes us with the means of 

 supplying it to commerce by the decomposition of the mu- 

 riate of soda or marine salt ; this is converted into a sul- 

 phate by means of sulphuric acid, and the last formed salt 

 afterward decomposed in a reverberatory furnace, in which 

 it is mixed with charcoal and chalk. 



The soda of commerce is never pure ; it contains at the 

 utmost but 30 or 40 per cent, of alkali : a solution of 

 it evaporated, yields octahedral crystals with rhomboi- 

 dal bases ; these crystals consist of alkali and carbonic 

 acid. 



