equal in density at 75° F., expanded or contracted equally on heating above or cooling below this temperature, their densities would always be identical. But inasmuch as orthotoluidine increases in volume to a greater extent than water on heating, and shrinks more on cooling, it becomes lighter than water when both are hotter than 75° F., and heavier when both are colder. We call the temperature when both are equal in density the _equi-density temperature_. Here are some figures which show how the densities of these two liquids diverge from a common value on heating or cooling, and which establish the conclusions we have drawn:— ─────────────────────────────────────────────────────────────────── Temperature. Density. Deg. F. Deg. C. Water. Orthotoluidine. ─────────────────────────────────────────────────────────────────── 50 10 0·9997 1·009 59 15 0·9991 1·005 68 20 0·9982 1·001 Equal: 75 24 0·9973 0·997 86 30 0·9957 0·992 95 35 0·9940 0·988 104 40 0·9923 0·983 ─────────────────────────────────────────────────────────────────── [Illustration: __Fig._ 8.—Aniline drops falling through cold water and ascending through hot water._]