144 CHYMISTRY APPLIED TO AGRICULTURE. 



it a large portion of mucilage, and is usually employed only 

 in some of the trades. In some countries it is customary 

 to collect the fruits into heaps, and to subject them to a 

 degree of fermentation before pressure; by this means the 

 extraction of the oil is rendered easier, and the quantity of it 

 is increased, but the quality of it is much injured. Similar 

 results are obtained by breaking the fruit previous to ex- 

 pressing the oil. 



It would be hardly right to condemn these last methods 

 as erroneous, because in the numerous soap-works, dye- 

 houses, cloth manufactories, &c., this quality of oil is 

 preferred to that which is purer. The learned will do 

 well to condemn the processes now employed for procur- 

 ing the fine oils, and to prescribe others by which we may 

 obtain them purer and of a better taste ; but the grand 

 consumption of the oils is in the manufactories, and there 

 the fine oils would very imperfectly replace those of a 

 coarser kind ; thus, by perfecting the produce, the useful- 

 ness of it would be lessened. When oil is to be extracted 

 for domestic purposes, it is without doubt desirable that it 

 be obtained as pure as possible; but that which is destined 

 to be employed in the trades, and in manufactures, as in 

 that of soap for instance, is the better for being combined 

 with a portion of mucilage. The great art of manufactur- 

 ing consists in appropriating the products to the wants and 

 tastes of consumers. 



When mucilage is so abundant in an oily seed, that it 

 yields upon expression only a pasty combination of muci- 

 lage and oil, the seed is dried by fire : when the mucilage 

 is thus deprived of fluidity, the oil flows off pure. In this 

 manner the seeds of flax, of poppies, of hen-bane, &c. are 

 prepared for expression. 



Nearly all oils are colored, and contain some of the 

 principles of the fruits from which they are procured ; these 

 are in some of their effects injurious to the oil, and great 

 pains has been taken to find some means of freeing it from 

 them. Oil is clarified to a certain degree merely by stand- 

 ing in a cool place in open earthen vessels; it forms a 

 deposit and is thus rendered purer, clearer, and better. If 

 oil is exposed to the sun it gradually loses its color. 



In order to clarify the oil of mustard, one per cent, of 

 sulphuric acid is put into a large earthen pan, into which 

 the oil is thrown and carefully stirred: the oii becomes 

 green, and upon being allowed to remain at rest, forms 



