I'm making a stock solution of xylene in water. The solubility of xylene in water is 200 mg/L (Andrews and Keefer 1949). The density of xylene is 864 mg/mL. Making 1 L stock solution is too much and a waste. 0.23mL (or 230µL) of xylene is equivalent to 198.72mg. To make the stock solution, if I add the 0.23mL of xylene to 50mL of water the concentration is 3974.40 mg/L. This is where I'm confused and I feel silly. I'm getting confused between the 198.72mg of xylene and the stock concentration 3974.40mg/L. Which one should I be looking at?