I read it in the book Peter Atkins

The endothermic dissolution of ammonium nitrate in water is the basis of the instant cold-packs that are included in some first-aid kits. They consist of a plastic envelope containing water dyed blue (for psychological reasons) and a small tube of ammonium nitrate, which is broken when the pack is to be used.

Could not understand why die water blue would have any physiological effect on a body. What type of physiological effect is he refering to?

  • 2
    The quoted part says psychological. – Jan Jun 19 '19 at 8:03

You wouldn't want it dyed blood red though!

But seriously, from:

Very Well Mind

we have:

Blue is a color often found in nature such as the pale blue of a daytime sky or the rich dark blue of a deep pool of water. It is for this reason perhaps that people often describe the color blue as calm and serene. Yet as a cool color, blue can sometimes seem icy, distant, or even cold.


Blue calls to mind feelings of calmness or serenity. It is often described as peaceful, tranquil, secure, and orderly.


Blue is often seen as a sign of stability and reliability. Businesses that want to project an image of security often utilize blue in their advertising and marketing efforts.

Color Psychology agrees with this view of blue.

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