How the Gas Pump Knows When to Shut Off

The first gasoline pump certainly didn't exist for the purpose of fueling cars - though Karl Benz was tinkering with the idea, cars weren’t even invented yet. Created in 1885, that first pump was there to dispense fuel for stoves and kerosene lamps. It sure came in handy when cars did enter the scene, though.

The shutoff valve didn’t come along until more than 50 years later. In 1939, Olean, New York, resident Richard Corson noticed a man filling a barrel with gas and thought about what a waste of time and efficiency it was. He was sure there had to be a better way, but it wasn’t until he went to the bathroom and heard the toilet flush that the solution hit him - a butterfly float. The hands-free device would allow more than one barrel to be filled at once. Corson sketched a plan which was quickly followed by a rough prototype.

His original invention paved the way for the automatic shut-off used on most pumps today. The next time you’re trading in your savings to fill up your tank, take a second to really look at the nozzle you’re putting in the tank (don’t do this when you’re holding the trigger down). You’re probably going to notice two things: a tiny hole at the tip of the spout and a tube connected to it that runs down the interior side of the spout.

The hole is called a sensing hole; the tube connects it to a diaphragm near the shut-off valve in the nozzle.

When you squeeze the handle and precious gas starts to flow up through the spout, this creates a vacuum in that tube, keeping the diaphragm neutral. When your tank is reaching its limit, the gas is at a level high enough to cover the sensing hole. Air can’t get through the sensing hole to the vacuum, which makes the atmospheric pressure move the diaphragm, which flips a switch in the automatic shut-off device Richard Corson had a hand in creating. The switch flips, and voila, your tank is full.

Phew. Who knew keeping your shoes gas-free was so complicated?

If you’re still confused (or just want more details), here are a couple of experts:
The Straight Dope
How Stuff Works

'Lime Disease' Could Give You a Nasty Rash This Summer

A cold Corona or virgin margarita is best enjoyed by the pool, but watch where you’re squeezing those limes. As Slate illustrates in a new video, there’s a lesser-known “lime disease,” and it can give you a nasty skin rash if you’re not careful.

When lime juice comes into contact with your skin and is then exposed to UV rays, it can cause a chemical reaction that results in phytophotodermatitis. It looks a little like a poison ivy reaction or sun poisoning, and some of the symptoms include redness, blistering, and inflammation. It’s the same reaction caused by a corrosive sap on the giant hogweed, an invasive weed that’s spreading throughout the U.S.

"Lime disease" may sound random, but it’s a lot more common than you might think. Dermatologist Barry D. Goldman tells Slate he sees cases of the skin condition almost daily in the summer. Some people have even reported receiving second-degree burns as a result of the citric acid from lime juice. According to the Mayo Clinic, the chemical that causes phytophotodermatitis can also be found in wild parsnip, wild dill, wild parsley, buttercups, and other citrus fruits.

To play it safe, keep your limes confined to the great indoors or wash your hands with soap after handling the fruit. You can learn more about phytophotodermatitis by checking out Slate’s video below.

[h/t Slate]

Why Eating From a Smaller Plate Might Not Be an Effective Dieting Trick 

It might be time to rewrite the diet books. Israeli psychologists have cast doubt on the widespread belief that eating from smaller plates helps you control food portions and feel fuller, Scientific American reports.

Past studies have shown that this mind trick, called the Delboeuf illusion, influences the amount of food that people eat. In one 2012 study, participants who were given larger bowls ended up eating more soup overall than those given smaller bowls.

However, researchers from Ben-Gurion University in Negev, Israel, concluded in a study published in the journal Appetite that the effectiveness of the illusion depends on how empty your stomach is. The team of scientists studied two groups of participants: one that ate three hours before the experiment, and another that ate one hour prior. When participants were shown images of pizzas on serving trays of varying sizes, the group that hadn’t eaten in several hours was more accurate in assessing the size of pizzas. In other words, the hungrier they were, the less likely they were to be fooled by the different trays.

However, both groups were equally tricked by the illusion when they were asked to estimate the size of non-food objects, such as black circles inside of white circles and hubcaps within tires. Researchers say this demonstrates that motivational factors, like appetite, affects how we perceive food. The findings also dovetail with the results of an earlier study, which concluded that overweight people are less likely to fall for the illusion than people of a normal weight.

So go ahead and get a large plate every now and then. At the very least, it may save you a second trip to the buffet table.

[h/t Scientific American]


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