Mr. M’Culla charges good copper at fourteenpence per pound:  but I know not whether he means avoirdupois or troy weight.

  Avoirdupois is sixteen ounces to a pound, 6960 grains. 
  A pound troy weight, 5760 grains. 
    Mr. M’Culla’s copper is fourteenpence per pound avoirdupois. 
  Two of Mr. M’Culla’s penny notes, one with another, weigh 524 grains. 
  By which computation, two shillings of his notes, which he
    sells for one pound weight, will weigh 6288 grains. 
  But one pound avoirdupois weighs, as above, 6960 grains. 
    This difference makes 10 per cent.
    to Mr. M’Culla’s profit, in point of weight. 
    The old Patrick and David halfpenny weighs 149 grains. 
    Mr. M’Culla’s halfpenny weighs 131 grains.
          
                                                     ------
                                         The difference is 18

Which is equal to 10-1/2 per cent. 
The English halfpenny of King Charles II. weighs 167 grains. 
M’Culla’s halfpenny weighs 131 grains.
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The difference 36

Which difference, allowed a fifth part, is 20 per cent.

ANOTHER COMPUTATION.

Mr. M’Culla allows his pound of copper (coinage included) to be worth twentypence; for which he demands two shillings.

  His coinage he computes at sixpence per pound weight; therefore,
    he laying out only twentypence, and gaining fourpence,
    he makes per cent. profit, 20
  The sixpence per pound weight, allowed for coinage,
    makes per cent. 30
  The want of weight in his halfpenny, compared as above,
    is per cent. 10
  By all which (viz. coinage, profit, and want of weight)
    —­the public loses per cent. 60

If Mr. M’Culla’s coins will not pass, and he refuses to receive them back, the owner cannot sell them at above twelvepence per pound weight; whereby, with the defect of weight of 10 per cent., he will lose 60 per cent.

The scheme of the society, raised as high as it can possibly be, will be only thus: 

For interest of their money, per cent. 8
For coinage, instead of 10, suppose at most per cent. 20
For l.300 laid out for tools, a mint, and house-rent,
charge 3 per cent. upon the coinage of l.10,000, 3
——­
Charges in all upon interest, coinage, &c. per cent., 31