What is the meaning of 挥发 here?

Question

Chemistry is not my thing. I like to make 拉面 at home, although I am not very good at it.

Reading the advice for the use of 拉面剂 I saw this:

拉面剂加到面粉里后会挥发，所以用量有浮动。

I usually add the 拉面剂 directly to the flour, but here they say that is not ideal.

What exactly fo they mean with 挥发？ Maybe smelly?

The recipe for information:

兰州拉面剂（蓬灰）参考比例； 面粉：500克 水 ：250克 盐 ：6-8克 拉面剂 ：4克（5倍的水把拉面剂化开，揉面时一边揉面一边往里加拉面剂化的水。） 拉面剂加到面粉里后会挥发，所以用量有浮动。(拉面剂可以量多一点，化的水可以多一些，一边揉面一边加拉面剂的水，直到面揉光，表里都没有面疙瘩，轻松能拉开不断，就可以拉面了！)有其它问题可以联系客服咨询解决！ 收到货满意请给个满五星的好评，谢谢您的支持和理解！

Answer 1

挥发 means volatile or volatilization in English. In serious scientific Chinese, it is only used to describe volatile due to thermal motion of molecule (a kind of 物理变化(physical change)). Substances like ammonia and vinegar can 挥发 into the air, so you can smell it.

But in this usage (apparently it is informal), it is not thermal motion. I searched the ingredient of 拉面剂 and shockingly found that many 拉面剂 contains Sodium Sulfide 硫化钠(Na2S). When dissolved in water and exposed to air, it would have chemical reaction and eventually turned into volatilizable Hydrogen Sulfide 硫化氢(H2S), so you can smell some bad smell (which is often described as the smell of 臭鸡蛋(bad eggs)).

Hydrogen Sulfide is very harmful to your health. As a result, there shouldn't be any Sodium Sulfide inside your 拉面剂. Also, it is not a food additives listed in Chinese National Standard for food additives (GB2760), so it is illegal to add it.

There is a lot of argument about the actual ingredient of 拉面剂, and I can't be sure which is right. But I found two articles from 人民网 and 人民日报(two of the Chinese official media), and they claimed that safe 拉面剂's main ingredient should includes 食用盐, 碳酸盐，磷酸盐 and 焦亚硫酸钠 (sorry for not being translated, I'm just lazy), which are just some common food-grade things.

Answer 2

挥发 means “迅速消散" (rapidly dissipates into the surrounding air due to the volatile nature of the substance) It is a chemical phenomenon

Water would "蒸发" (evaporate) because the dryer air would carry the moisture away from the wet area. It is a physical phenomenon, higher temperatures would accelerate the process

易挥发的 = volatile. Day-to-day volatile objects include blench and paint thinner

Answer 3

挥发 means "turn into vapor" and is generally used for VOC (volatile organic compounds) or any liquid that's not water (e.g. alcohol). OTOH, 蒸发 is reserved for water.