Surface tension is a property of liquids that results from the cohesive forces between liquid molecules at the liquid-gas interface. It is the force that holds the liquid surface together and causes it to minimize its surface area. Surface tension is typically expressed in units of force per unit length, such as dynes/cm or mN/m.The drop weight method is a technique used to measure the surface tension of a liquid. In this method, a liquid droplet is formed by allowing the liquid to flow through a small opening usually a thin tube or a needle . The surface tension of the liquid can be determined by measuring the mass or volume of the liquid droplet and the force required to detach it from the opening.Here are the steps to measure surface tension using the drop weight method:1. Set up the apparatus: The apparatus consists of a thin tube or needle connected to a liquid reservoir, a sensitive balance to measure the mass of the droplet, and a mechanism to control the liquid flow rate.2. Clean the tube or needle: It is essential to clean the tube or needle thoroughly to remove any contaminants that may affect the surface tension measurement.3. Fill the reservoir with the liquid: Fill the reservoir with the liquid whose surface tension you want to measure, ensuring that there are no air bubbles in the liquid.4. Adjust the flow rate: Adjust the flow rate of the liquid so that droplets form at the tip of the tube or needle at a consistent rate.5. Measure the mass of the droplet: As each droplet detaches from the tube or needle, measure its mass using the sensitive balance. Repeat this process for several droplets to obtain an average mass value.6. Calculate the surface tension: The surface tension can be calculated using the following formula: = mg / 2r where m is the mass of the droplet, g is the acceleration due to gravity approximately 9.81 m/s , and r is the radius of the tube or needle opening.By following these steps and using the drop weight method, you can accurately measure the surface tension of a liquid.