Determination of relative density by density flask method
The relative density can be calculated by measuring the mass of water and sample filled with the same density bottle at 20 ° C. The density bottle method is the most accurate method for measuring the relative density of liquids. It is suitable for measuring the relative density of various liquid foods, especially for small sample quantities. It is also suitable for volatile samples, but the operation is more cumbersome.
1. Determination method
(1) Weigh the empty bottle first, wash the density bottle, then wash it with ethanol and ether in turn, dry and cool it, and weigh it precisely on the analytical balance together with the thermometer and side tube cap.
(2) Weigh the sample liquid, remove the thermometer and side tube cap, fill the sample liquid, insert the thermometer, immerse it in a 20 ° C constant temperature water bath for 0.5 hours, so that the temperature of the contents reaches 20 ° C. Use filter paper to suck off the sample liquid on the branch pipe marking line, cover the side tube cap and take it out. Dry the water on the outer wall with filter paper, place it in the balance room for 30 minutes and weigh it.
(3) Weigh the distilled water, pour out the sample solution, wash the density bottle, fill it with distilled water that has been boiled for 30 minutes and cooled to below 20 ° C, and operate according to the above method. Measure the quality of the same volume of distilled water.
2. Instruments
The density bottle is a special instrument for measuring the relative density of liquid foods. It is a fixed-volume weighing bottle (with specifications such as 20mL, 25mL, 50mI, 100mL, etc.), which is divided into precision density bottles with thermometers and ordinary density bottles with capillaries.
3. Precautions
① This method is suitable for determining the relative density of various liquid foods, and the results are accurate, but the operation is cumbersome.
② When measuring a more viscous sample, a density bottle with a capillary should be used.
③ The density bottle should be of constant weight before use, and check whether the bottle cap and bottle are matched; the water and samples must be filled with the density bottle, and there must be no bubbles in the bottle.
④ When maintaining a constant temperature, it is necessary to use a filter paper strip to absorb the overflowing liquid in a timely manner, so as not to allow the liquid to overflow onto the bottle wall. When taking a density bottle that has reached a constant temperature, do not directly touch the ball of the density bottle with your hands to avoid the liquid from being heated out. Wear thermal gloves to remove the bottleneck or use a tool to clamp it.
The water used in the water bath must be clean and free of oil to prevent the outer wall of the bottle from being contaminated.
The temperature of the balance chamber should not be higher than 20 degrees Celsius to prevent the liquid from expanding and flowing out.
