Another use of density is determining the percentage of fat in a human body. With a well-engineered weighing system, body density can be determined with great accuracy by completely submerging a person in water and calculating the volume of the displaced water from the weight of the displaced water. Fat cells in humans are composed almost entirely of pure triglycerides with an average density of about 0.9 kg/L. (kg/L are equivalent ot g/mL, but easier to use with larger objects like the human body.) Most modern body composition laboratories today use the value of 1.1 kg/L for the density of the “fat free mass”, a theoretical tissue composed of 72% water (density = 0.993), 21% protein (density = 1.340) and 7% mineral (density = 3.000) by weight. A correction is made for the buoyancy of air in the lungs and other gases in the body spaces. To find the percentage of fat we can assume that, if we set x to the fat percentage, 100 – x is the rest of the “fat free mass” of the body. The calculation is: Density of the body = (0.9)x + (1.1)(1-x)Rearranging the equation to solve for x allows the calculation of the fraction of the body that is fat. Multiplying by 100 gives the percent fat. A 35 year-old female has a mass of 78 kg. When placed in a tank containing 1000. L of water the volume in the tank increases to 1075 L. Find the woman’s fat percentage and from the table below, determine if she is considered healthy. The density of pure water is 1.00 g/mL, but very few water samples have this actual density. The density of the Mississippi River in southern Louisiana is measured at .999 g/mL. The density of the salty water in the Gulf of Mexico can get as high as 1.035 g/mL. At the mouth of the river the fresh water mixes with the salt water of the Gulf. If we had 50.0 mL of the river water and we mixed it with 100.0 mL of the gulf water, what would the new density be? Density of the body = (0.9)x + (1.1)(1-x)Rearranging the equation to solve for x allows the calculation of the fraction of the body that is fat. Multiplying by 100 gives the percent fat. A 35 year-old female has a mass of 78 kg. When placed in a tank containing 1000. L of water the volume in the tank increases to 1075 L. Find the woman’s fat percentage and from the table below, determine if she is considered healthy.