Reply to Burridge & Linden: Hot water may freeze sooner than cold

TL;DR

This paper clarifies the true nature of the Mpemba effect, emphasizing its relation to freezing rates rather than cooling rates, and presents a theoretical prediction that it occurs only in hard water with dissolved minerals.

Contribution

It corrects a common misinterpretation of the Mpemba effect and provides a theoretical explanation predicting its occurrence only in hard water, which remains to be experimentally tested.

Findings

The Mpemba effect relates to freezing, not cooling.

It occurs only in hard water with dissolved minerals.

A theoretical model predicts the effect's dependence on water hardness.

Abstract

In a recent paper in Scientific Reports, Burridge \& Linden misinterpret the Mpemba effect as a statement about the rate of cooling of liquid water, when it is in fact a statement about the rate of freezing of water. Debunking an obviously absurd claim about cooling, they miss the significant effect, its only quantitative experimental study and a theoretical argument that explains the effect and predicts that it occurs only for "hard" water (water with significant dissolved Mg and Ca bicarbonates). This prediction remains to be tested.