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一、比重计上为什么没有单位这就得从什么叫物质的“比重”谈起了。早先,人们把同体积的水银、酒精等和水的重量相比,其倍数就叫做水银、酒精等的“比重”。水银的比重=(ρ水银gV)/(ρ水gV)=(ρ水银)/(ρ水)=(1.36×10~3)/(1×10~3)=13.6所以水银的比重是13.6,它就没有单位了。同样,酒精的比重就是0.8,有时说配制的盐水的比重是1.25等。所以比重计是在这种意义上测定液体的。然而,我们现在是用它来测定液体的密度,只要把比重计上的读数乘以10~3千克/米~3,就可以了。二、比重计的刻
First, why do you have no units on the hydrometer? This has to start with what is called the “specific gravity” of the material. Earlier, when people compared the weight of mercury, alcohol, and water in the same volume, the multiple was called the “proportion” of mercury and alcohol. The proportion of mercury = (ρ mercury gV) / (ρ water gV) = (ρ mercury) / (ρ water) = (1.36 × 10 ~ 3) / (1 × 10 ~ 3) = 13.6 so the proportion of mercury is 13.6, It has no unit. In the same way, the proportion of alcohol is 0.8, and sometimes the proportion of formulated salt water is 1.25. So the pycnometer measures the liquid in this sense. However, we are now using it to determine the density of the liquid, as long as the reading on the pycnometer is multiplied by 10~3 kg/m~3. Second, the hydrometer of the moment