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pointed out that, using Edwards' wash proportions, the planter would run out of scum before being able to make enough washes to produce a ratio of 4.2 gallons or 4.5 gallons of rum to cwt. of sugar. In fact, using Edwards' wash compound, a sugar plantation of the size and specification that Edwards identified would only produce about 65 washes of 1,200 gallons, which, based on the rum to low-wine ratio, only produced 8,094 gallons of proof rum, or 2.5 gallons of rum per cwt. of sugar.
In an attempt to fix the error, McCusker reassessed Edwards' wash compound.
McCusker accepted Edwards' figures for the availability of scum and molasses, but argued that the average Jamaican wash must have contained 12 gallons of scum and 10 gallons of molasses. This ratio of scum and molasses still provided the wash with the necessary 12% level of sweets. As a result, McCusker's model had enough scum and molasses to make 100 washes and 11,300 gallons of rum. For a plantation making 200 hogsheads of sugar at 16 cwt. this produced a ratio of 3.5 gallons of rum per cwt. of sugar.
According to McCusker, the "demonstrated" level of rum production from two
Jamaican plantations supported the 3.5-gallon ratio. Although not explicitly stated, the ratio also reflected Long's estimate of Jamaican rum production for the period 1768-1772, the period McCusker was most interested in explaining. Long (1774;II:228-229) argued that a typical Jamaican plantation of 300 acres produced 3.57 gallons of rum per cwt. of sugar. Within the same paragraph, Long also wrote that Jamaica as a whole produced 3.53 gallons of rum per cwt. of sugar. Thus, the revision of Edwards' wash compound may reflect McCusker's attempt to match Edwards' rum production figures to those described by Long for the period 1768-1772.
McCusker's estimates were based on Edwards' statement that a 1,200-gallon wash produced 113 gallons of rum. McCusker simply multiplied 113 gallons of rum by 100; the number of washes available using the new wash ratio. By doing so, McCusker arrived at 11,300 gallons of rum for a ratio of 3.5 gallons of rum per cwt. of sugar. However,