In July 1890, the Wisconsin Agricultural Experiment Station in Madison issued a bulletin describing a test any creamery operator could run with a glass bottle, a dose of sulfuric acid, and a hand-cranked centrifuge. Its author, the station's chief chemist Stephen M. Babcock, had found a cheap way to measure something nobody had ever been able to measure cheaply before: how much butterfat was actually in a given can of milk.
Before the test, most creameries and cheese factories paid by the pound or the gallon, the same price for every delivery no matter what was actually in it. Babcock wrote a few years later that many factories still clung to that method, paying the same price for all milk independent of its quality, and that doing so was inviting the fraud his bulletin went on to describe: a farmer could skim the cream from a can before the wagon left, or thin it with water, and be paid exactly as much as the neighbor who sold it whole. Wisconsin's legal minimum for milk was three percent butterfat, and selling milk below it as pure was illegal whether the shortfall came from watering, skimming, or poor cows.
The fix needed no new law and no lawsuit. Babcock's test mixed a measured eighteen grams of milk with an almost equal volume of sulfuric acid, strong enough to dissolve the casein and other solids and free the butterfat; a centrifuge then spun the bottle for about five minutes, after which hot water was added to carry the fat up into a graduated glass neck, and a second, shorter spin settled it there before anyone could read the percentage straight off the scale. A creamery no longer needed a trained chemist or much trust in its suppliers, only the bottles, acid, and centrifuge already in the bulletin and a few minutes to use them, and it could know, for any farmer's can, what had actually been delivered.
Babcock and the university gave the test away. The station's director, W. A. Henry, wrote in the following year's report that it had been given to the dairy world without restriction by patent, or limitations in any way. The first printing of ten thousand bulletins sold out, and a second printing of the same size went just as fast; manufacturers in several states had already begun building the glassware, and letters of inquiry arrived, Henry noted, from every part of the country and from other countries besides.
What changed was not enforcement. It was the price of knowing. Once butterfat could be measured cheaply and quickly, no inspector had to go looking for cheats, because there was no more profit in being one. The system makes it the interest of every man to supply as good milk as possible, Babcock wrote of his own invention. He did not mean it as sentiment: honesty had stopped costing the honest farmer anything, because dishonesty no longer paid.
A gallon of water still weighs about the same as a gallon of milk. The difference used to show up only in the price. After 1890, anyone with a bottle and a few minutes could read it instead.