The temperature where a substance’s liquid and solid forms coexist in equilibrium. The value varies with pressure and is affected by purity; it is also known as the melting point. Freezing-point measurement can detect watering of milk, since the value rises when water has been added — the basis of the cryoscopic test in dairy quality control. Milk’s freezing point — around −0.52 to −0.56°C — is set by its lactose and mineral content, and added water shifts it measurably toward zero; cryoscopes detect adulteration down to a few percent. The same principle governs ice-cream hardness (sugars depress the freezing point) and the brines used in immersion freezing.