212 VEGETABLE SUBSTANCES. 



duce good seed-oils do not end with their mere 

 extraction. 



Notwithstanding all the precautions which are 

 used in each operation, some particles of the vesicles 

 of the seeds unavoidably find their way into the 

 cistern, and these gradually subsiding, cause the 

 fluid to be in strata of different purities. The pumps 

 constructed for drawing off the oil are there- 

 fore made to work in pairs, the one bringing it up 

 from the bottom, the other from about the middle : 

 that coming from the latter is the oil barrelled up for 

 sale, the other is conveyed to a deep narrow cistern, 

 where subsidence again takes place and more pure 

 oil is obtained. 



The advantages of superior machinery and care- 

 fulness of process, cannot be more strongly exem- 

 plified than by instancing the Dutch oil-mills. The 

 price of labour, as well as of materials for erecting 

 machinery, are comparatively high in that country. 

 Wind is generally made the moving power in these 

 mills, and the complicated construction of windmills, 

 and the keeping them in repair, are attended with 

 enormous expense. Yet the Dutch are not only 

 enabled by their superiority in this branch of in- 

 dustry to compete with other countries in so im- 

 portant an article of commerce, but likewise to send 

 annually considerable quantities into the very pro- 

 vinces of France and Flanders, where they buy part 

 of the seed from which it is extracted. The greater 

 part comes from Riga. In the seigneurie of Lille 

 alone, between thirty and forty thousand barrels of 

 oil, each containing about twenty-six gallons, are 

 annually made from seeds*. 



The oil of several other kinds of seed is advan- 

 tageously used as well as rape oil in many manufac- 

 tories and trades. Among these are mustard and 

 * Nicholson's Operative Mechanic. 



