英语时差：为何食盐不黏在一起？

Our last program talked about table salt, technically called sodium chloride, which is available in iodized form–that means that it includes a small amount of potassium iodide or sodium iodide added to the sodium chloride. Iodized salt is intended to supply us with the chemical element iodine, an essential nutrient. Iodized salt has been available in the United States since 1924. Sticky Situation But a table-salt additive even more common than iodine is some anti-caking agent, to keep the salt crystals from sticking together as they absorb moisture from the air. Salt crystals are made of sodium and chlorine atoms linked together like Tinkertoys to form a three-dimensional framework. Because the atoms are evenly spaced and the connections between atoms are at right angles, sodium chloride crystals take the form of cubes. Those cubes can pack closely together, like children’s blocks. As those closely-packed cubes absorb water from the air, they partially dissolve and fuse together.