Milkmans puzzle

Puzzle

There are practical problemss in all trades, so it is safe to say that no one is an adept at his business unless he has picked up a few wrinkles which pertain to his calling.
Honest John says that what he "don't know about milk is scarcely worth mentioning," but he was nearly flabbergasted once when he had nothing but two ten gallon cans full of milk, and two customers with a five and a four quart measure wanted two quarts put into each measure.
It is a juggling trick pure and simple, devoid of trick or device, but it calls for much cleverness to get two exact quarts of milk into those measures employing no receptacles of any kind except the two measures and the two full cans. You can try the problem with the fullest assurance that it is a legitimate proposition and not a silly catch.

Answer

References

• Loyd, Sam [1914]. in Loyd, Sam, Jr.: Sam Loyd's Cyclopedia of 5000 Puzzles Tricks and Conundrums (in English). New York: Lamb Publishing company, page 52.