264 VEGETABLE SUBSTANCES. 



the seed. At the first appearance of spring, the 

 ground is cleared of weeds, and kept so throughout 

 the summer. The barilla is in a fit state to be col- 

 lected when it is in its decline, or after the greater 

 part of the seed has arrived at maturity ; and this 

 usually happens in the month of September. It has 

 very small roots, and is therefore readily torn up; 

 after which it is dried in the same manner as grass 

 is made into hay. It is sufficiently dry when so 

 much of the succulent moisture is exhaled, that it will 

 readily burn. A greater dryriess, such as may be 

 caused by a too long exposure to the sun in hot 

 countries, is injurious to the barilla ; as the combus- 

 tion is in consequence too rapid, which not only 

 lessens the quantity of alkaline salt, but likewise in- 

 jures its quality. 



About the middle of October the plants are burnt. 

 For this purpose hemispherical holes are made in 

 the earth, capable of containing about thirty hundred 

 weight of soda. Two iron bars are laid across each 

 of the cavities, and the plants mixed with straw and 

 reeds are placed on these supports. 



This process is never commenced on a day when 

 the wind is high, lest it should cause a too rapid 

 combustion ; for when the plants are so quickly 

 burnt, the barilla is less easily reduced to a solid 

 mass. On the other hand, a perfect calm is not the 

 most favourable to the operation, as the smoke is not 

 then sufficiently carried off, and injures the purity of 

 the alkali. The action of the fire fuses the soda 

 which is in the plant, and it flows into the cavity 

 beneath, in the form of a red-hot fluid mass. The 

 combustion is continued until the pits are full, to 

 accomplish which generally occupies a whole night. 

 The alkali is then stirred once or twice to encourage 

 the more intimate union of the parts ; after which, 

 being covered with earth, it is left to cool during ten 



