About Red Squirrel's experiment with plain and salted water freezing:
I'm a Physical Chemist, so I understand the theories on this. Bottom line is, what he saw should not happen if all other items are matched. So we start looking at how come it did not work aqccording to theory?
General rule: when you make a solution by dissolving something (salt, here) in a pure solvent (water), the solution's freezing point always will be LOWER than that of the pure solvent. That is why road salt helps ice to melt, and auto antifreeze prevents your radiator from freezing, and common sugary soft drinks do not freeze as easily as water. But that's just the TEMPERATRE at which freezing will start to happen.
The matter of HOW FAST the freezing will happen is different, especially if the surrounding temperature (really cold air) is very much colder than the expected freezing point. The How Fast part can be affected by other things, like what temperature each different beaker of solution started at to begin with, because the entire beaker full must first be cooled down to the freezing point. Also, how much solution was in each beaker, since that affects how fast the initial liquid can be cooled. And of course, air currents in the area that affect how fast heat can be removed from the beaker are important. And finally, a more subtle item: was all the salt actually dissolved before starting? In the process of initiating the formation of solid crystals from a liquid, there's a factor called crystal nucleation. That is, if there is some foreign solid material (a tiny salt crystal not already dissolved, or a piece of dust, or even a rough scratch on the inside of the beaker) in the solution, that is where the first crystals will form. And once there is a tiny crystal, more will build up on it, making the solidification process proceed quickly. On the other hand, if there is no such nucleation particle present (say, in the plain water), sometimes the liquid actually has to get BELOW the freezing point (this is called supercooling) by a bit before some initial crystals suddenly form, and then the process can proceed normally.
So what Red Squirrel's experient really did was to examine the RATE of freezing of the two solutions. This is not quite the same as the exact TEMPERATURE at which each of the two solutions would just START to freeze. The addition of modest amounts of salt to water to make a solution would make small changes to the heat acpacity and thermal conductivity of the resulting solution, but not enough to make a substantial change in results. Beyond that, depending of just how much salt was added, the freezing results over time and temperature get more complex as we look at what is called the binary system phase diagram of the freezing of a liquid solution.
) the salt one actually started to freeze even further. Since I had no clock capable of surviving the cold temps I had to get a bit creative with a timer overlay and no idea how accurate it is, but once I got it all figured out I'll make a separate thread. It's kinda neat to see. Nothing ground breaking here, just thought it was neat to try. 
Facebook
Twitter