It's a footnote on p. 65 of the 1957 (1st?) edition: "Once the Philadelphia Mint ... makes us richer. This is now known as Bloom's Law on the Profitable Inertia of Gold."

Regarding Bloom's Law, the figure of $5 per $1m or 5 parts per million (ppm) lost by abrasion in one manipulation is in line with other estimates. In the 1830s the French government sorted by year and individually weighed 400,000 silver pieces, to measure wear. They noticed that the coins, after the manipulations were done, had lost in aggregate 16 ppm. The annual loss on gold coins in the 19th c. ranged from 100 to 1000 ppm depending on country and denomination.