3l6 On the Manufacture of Muscovado Sugar. 



powers was chiefly attended to : in the instruments whicli 

 are now to be made, the utmost convenience will be at* 

 tained ; and from these only the descriptions and models, 

 which I shall soon lay before the honourable members, are 

 to be made. 



At the present moment I must content myself with pre- 

 senting a few lines descriptive of the principles upon which 

 a small simple filtrating instrument is competent to the in- 

 tended uses. 



In ordinary cases, the power by which the liquor is pressed 

 through the interstices of a filtrating cloth is merely the 

 weight of the liquor; and, under equal pressures by weight, 

 the velocity of filtration is as the extent of filtrating cloth. 

 But, as in ordinary vessels used for this purpose, the pressure 

 on a given area of the filtratino; surface increases with the 

 height of the liquor above it, oniitting nice discussions, we 

 niav affirm generally, that the velocity of filtration is as the 

 number of square inches of filtrating cloth multiplied by the 

 height of the contained pressing fluid ; therefore, in order to 

 attain any required velocity of filtration, the height of the 

 pressing column may be made to compensate for any de- 

 sirable reduction of the size of the cloth. 



Supposing, for instance, a cloth measuring 8 feet by 7-1-, 

 or 60 square feet in area, could filter fast enough under a 

 charge of liquor measuring 3 inches in depth, one-sixth of 

 this cloth, or 10 square feet of it, would serve if the column 

 or charge of liquor pressing on it were made to be 18 inches 

 in height : and with the height of 36 inches, 5 square feet 

 would serve ; and tliis is less than the measure of a common 

 pocket handkerchief. 



By the like reasoning it will be found, that if the cloth of 

 60 square feet filter no quicker than is necessarv for the pro- 

 gress of the manufacture, the filtration will become slower 

 as the liquor lowers to a smaller area of filtrating surface, 

 and still slower as the height of the pressing liquor de- 

 creases; so that at the heiglit of one inch, the quantity fil- 

 trated in a given time would be much less than one-third of 

 that which the progress of the work would require. 



But when it is considered that filtration will not avail 



much 



