The addition of salt to detergent does not involve the development or application of any physical theories in the same way that scientific theories are used to describe fundamental aspects of nature. Instead, the addition of salt to detergent is based on empirical observations and practical considerations.
The primary reason for adding salt to detergent in laundry is to enhance its performance under certain conditions. Salt can assist in various ways:
Water softening: Hard water contains high levels of minerals like calcium and magnesium, which can interfere with the effectiveness of detergents. Salt can act as a water softener by binding to these minerals and preventing them from interfering with the detergent's ability to clean.
Stain removal: Salt can aid in stain removal by improving the solubility of certain substances, especially for stains caused by proteins (such as blood or sweat) or tannins (such as those found in tea or coffee). It helps to loosen and lift these stains from fabric fibers.
Color preservation: Salt can help prevent the bleeding of colors in fabrics. When added to the wash, it can help set dyes and minimize color transfer between garments.
These effects of salt in laundry are not based on any specific physical theories but are rather practical observations and techniques that have been developed over time. The use of salt in laundry is a well-established practice based on empirical knowledge and experience rather than being driven by a particular scientific theory.