It’s Not Melting, It’s Dissolving

Time for another post where I get on my science grammar soapbox. Have you ever seen the movie The Wizard of Oz? Everyone has seen that movie, right? Recall the scene where Dorothy throws a bucket of water on the Witch, and the Witch dissolves into a puddle while screaming “I’m melting, I’m melting”? First, don’t ever watch that movie with me. Why? Because every time I see that scene, I scream “you’re not melting, you’re dissolving, get it right.” Ok, it is a movie, a movie that takes place where monkeys fly, there are witches, lions walk and talk like humans, and scarecrows come to life. No, I shouldn’t be looking for realistic science in it. However it drives me crazy that they can’t even get the simple difference between dissolution and melting correct.

In the exact same incorrect way, there is a saying that some people say when their children, dog, whatever, is hesitate to go outside in the rain. “You are not made of sugar, you won’t melt.” There are actually several things wrong with that statement. Sugar, as in table sugar, which is specifically sucrose (as opposed to all the other sugars that exist), does not actual melt at all. At 186°C (367°F), it decomposes to caramel. So even if that saying meant decomposes, if the temperature outside is high enough for sugar to decompose, you have much bigger problems then possibly getting wet. You would die of heat. However, if you were made of sugar, and you went out into the rain, you would not have to worry about melting, you would have to worry about dissolving.

Melting is a physical process where solid turns into a liquid due to heat applied to it. Stick ice into a glass at room temperature. Wait a while. You now have water in the glass. The ice melted into water. But you didn’t apply heat, you might argue. The melting point of ice, the temperature at which solid water, i.e. ice, becomes liquid water is 0°C (32°F). So by simply having ice at room temperature (around 22 °C (72 °F)), heat has been applied to it. The temperature is higher than what the ice needs to stay a solid. Similarly put solid chocolate in a pot and heat slowly to 30°C (86°F). You have liquid chocolate. It has melted. Now don’t waste that chocolate, go eat it with strawberries or cake. [Excuse me for a moment. . .]

Now take that glass of water you made by melting ice at room temperature, and pour just a little salt into it. The salt has dissolved into the water. The water, which is the solvent, has dissolved the salt, the solute, into a solution. When Dorothy throws water on the Witch, the Witch is the solute, the water is the solvent again, and now you have a witch solution in water. Based on the film, witch dissolves quite readily. [It would not matter if she threw boiling water on the Witch, it would still be dissolution because the water is mixing with the witch. The water was quite clearly not boiling anyway.] Other liquids can act as solvents to dissolve solutes, but water is the most common in everyday life. Wiping acetone on nails painted with nail polish removes the polish because acetone, a solvent, dissolves the hardened nail polish, the solute, into a solution. [It is a temporary solution in the sense that acetone readily evaporates, but it forms a solution with the polish long enough to transfer the polish to a cotton ball. The acetone then evaporates leaving behind the polish on the cotton.] An important distinction between melting and dissolving is that melting only involves one substance, water, chocolate, wax, etc. Dissolution involves two substances, water and salt, water and sugar, acetone and nail polish, etc. Dissolution can also involve applied heat, but it isn’t required. There is a much longer explanation for that, and it relates to the solute and solvent and numerous other factors.

To review, melting is one substance changing from a solid to a liquid, and one, and only substance is involved. It is a phase change that must involve a temperature (or pressure) change. Dissolution is one substance becoming part of a solution with a liquid, and two substances are involved. It is two substances becoming one, and temperature change is not necessary for it to happen.

I honestly don’t understand why some people don’t understand the difference. However ignorance of this appears to be wide spread. Evidently the U.S. Special Inspector General for Afghanistan Reconstruction does not know the difference. That Inspector General recently released a report concerning a half-million-dollar U.S.-built police training center in Afghanistan that was so badly constructed that it is literally “melting.” Nope, it is not. It is literally dissolving. If the center had been made of wax, then maybe it might melt. Based on the wording in this article and the accompanying photos, the building is quite clearly dissolving. That is still incredibly appalling construction. As an engineer, I would really like to see the design plans. However, if the Inspector General does not even know the difference between melting and dissolving, then perhaps the Inspector General would do well to have someone on staff who does. It would make for better and more accurate reports.

Mu is Not U

Time for another blog post where I try to improve science grammar.

This is the lower case Greek letter mu: μ. This is the lower case Latin letter u: u. Latin letters are, of course, what are used in the English alphabet as well as many, many other languages. While μ and u look similar, they are different. The Greek letter mu, uppercase Μ, is closer to the Latin letter M. The Latin letter U (uppercase, or u, lowercase) is more related to the Greek letter Upsilon (uppercase Υ, lowercase υ).

So now that I got that out of the way, when it comes to science in particular, μ and u are NOT interchangeable. In the International System of Units (SI), otherwise known as the Metric system, μ is the symbol used to represent the prefix micro-. “μ” can easily be added into a document using a insert symbol compound. It is an easy procedure, and there is no need to be lazy and just use “u”. “u” does not mean micro-. It is wrong. Don’t do it.

Kilograms Do NOT Measure Weight

I think like many engineers, one of the reasons that I liked the idea of going into engineering was the mistaken belief that a career in engineering meant working with numbers and not having to write. I have never been very good with words. I love numbers. Numbers make sense to me. Words confuse me at times. Also, the English language in general makes no logical sense to me, and I am a native English speaker. [Well, I’m a Southern, so you can go ahead and make an argument against the native English speaker part.] I can’t spell worth crap because of the aforementioned English language illogical thing. This is actually fairly common among engineers. Had my family known the warnings signs, it would have been obvious since I was about 5 years old that I was destined to be an engineer. I have always been good with numbers, and I can’t spell worth crap. Take note parents, as these are the warning signs your child may be an engineer. Also, an early love of duct tape.

I am fairly good with grammar though probably because there are more rules and less exceptions. Partially because of this and for other reasons, at my current job, I often edit other people’s documents not just for science and engineering accuracy but also for grammar, readability, and clarity. I have also been a peer reviewer for a few manuscripts submitted to scientific journals, and previously, I used to edit manuscripts that were about to be submitted to peer review journals. I keep coming across certain words and phrases that are scientifically and grammatically incorrect. There are many grammar style manuals that exist, but I have yet to come across a science grammar style manual. If one exists, I would love for someone to point me to it. So I’ve decided to start writing about some of the most common and inappropriate phrases in the hope that maybe it will stop at least one one person from using these incorrect phrases.

The most common and completely wrong phrase I see is stating that something or someone weighs a certain number of kilograms. Ironically, non-US citizens, i.e. people who live in a country where they use the metric system, are just as guilty of this phrase as US citizens who sort of have the excuse that they live in a country that refuses to stop using the completely archaic and impossible to use if you are a scientist or engineer, English imperial or US customary units. For the benefit of everyone who doesn’t understand why this is wrong, let me explain why it is.

A kilogram is a unit of mass. Mass is the amount of stuff that an object has.

To say something weighs something, you are saying it has a certain amount of weight. A weight is a specific type of force, and because it is a force, weight, like all other forces, is measured in Newtons (N) in the metric system. Weight is the amount of force on an object due to gravity. Therefore, weight is the mass (the amount of stuff) multiplied by the acceleration due to gravity. If you happen to be a person on Earth with a mass of 70 kg, then since the gravitational acceleration on Earth is 9.81 m/s2, you have a weight of 687 Newtons (N). Let’s say you happen to be an astronaut, and the Moon program gets revived, and you go to the moon. Your mass will not change. Your mass will still be 70 kg, but once you arrive at the Moon, your weight will be about 114 N because the Moon’s gravitational acceleration is 1.63 m/s2. While you are on your journey to the Moon in space, there will be no gravity, so you will have no weight. You will be weightless, hence the fun videos of astronauts floating, but you will still have the same 70 kg mass.

To review, a person or an object has a mass that can be measured in kg. A person or an object that is on any celestial body with gravity has a weight that can be measured in N. It is completely incorrect to say that a person or an object has a weight in kg. It is also confusing. Does it mean you have a mass in that number of kg? Does it mean you have a weight in that number of N, not kg? Please, don’t use kg and say weight. Mass and weight are not interchangeable. They do not mean the same thing.