Sodium chloride is used in a wide variety of biochemical applications, including intravenous fluids (normal saline is 0.9% w/v in water), density gradients, a diluent to increase ionic strength in buffers or culture media and in salt-out procedures in the isolation of DNA. It has also been used in high concentrations for preservation of foods since bacteria cannot grow in high salt conditions. A salt-ice mixture in the ratio of approximately 33 g sodium chloride to 100 g ice (at -1 C) will drop in temperature to as low as -21 C, depending on the rate of stirring and the size of the ice chunks.