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FOR THE USE OF
THE COMPARATIVE RULE.
ON the side of the Rule marked A B, is found the comparative values of spirits of different strengths; and on the side marked CCC, the amount of water required to reduce from one strength to another. Upon the side A B, the line A denotes shillings per gallon, from six to thirty shillings. The line B from one shilling and sixpence to eight shillings per gallon. The sliding centre comprises the different strengths from 70 under to 70 over Proof. The figures to the left of the word "Proof" indicate under Proof to the right, over Proof.
Example, on side A B, line A. Suppose a spirit 25 over Proof worth twenty shillings a gallon. Move the slide until the 25 to the right of "Proof" is in line with figure 20 on line A, then opposite every strength indicated on the sliding centre will be found the proportionate values. Thus 'Proof will be worth sixteen shillings per gallon; 15 under Proof, thirteen shillings and sevenpence per' gallon. 25 under Proof, twelve shillings per gallon.
Example, on side A B, line B. Suppose Proof spirit to be worth six shillings per gallon, and set the word "Proof" in line with 6 on line B; then 10 over Proof is worth six shillings and sevenpence per gallon, and 50 under Proof three shillings per gallon.
On the side CCC, the upper line is divided from 300 to 60 parts, and the lower from 100 to 20, denoting gallons; the sliding centre, as in the former case, indicating percentage of strength. Example, Assume 90 gallons of spirit, 30 over Proof are required to be reduced to Proof. Slide the centre until the figure 30 to the right of "Proof" coincides with 90 on the upper line. Then, on the same line, "Proof" will be found to coincide with 117, being the number of gallons it is to be made up to. To reduce the same quantity and quality to 20 under Proof would require to be made up to 146 gallons. Again, assume that a cask of 120 gallons is required to be filled with spirit 35 under Proof; slide 35 to the left of "Proof" until it is opposite 120 on the upper line, and on same line at 20 under Proof, 97½ gallons will be shown as the quantity of spirit of that strength required. If 15 under Proof, then 91 2/3 gallons; if Proof, 77 ¾ gallons; if 20 over Proof, 65 gallons; the remainder to be made up with water. The bottom line C carries the same principle down to smaller quantities; for instance, a cask is required to contain gallons of spirits, 30 under Proof, slide 30 on the ft of "Proof" until opposite 40 on the lower line, and it will then be found that 31 gallons of 10 under. Proof, or 35 gallons of 20 under Proof, or 25½ gallons of 10 over Proof will suffice, with the addition of the difference in water, to make up the 40 gallons of the required strength.
This side of the Rule may also be used for reducing stocks to one general value by placing the actual strength of the spirit on the sliding centre opposite the quantity on the upper line, the quantity on the same line and opposite the strength at which it has been agreed to take the stock will be found the exact equivalent in gallons of such spirit. Example, in 140 gallons of spirit 40 under Proof, how many gallons of 28 under Proof? Place the figure 40 to left of "Proof" under 140 on the top line, and on same line opposite 28 on the sliding centre will be found 116½, the number of gallons at 28 under Proof. For smaller quantities than 20 gallons call 100=10, 180=18, 90=9, and so on.
Return to Proof Rule in collection
My thanks to Jim Bready who provided the scanned images of the text.