Fahrenheit hydrometer

Operation

The Fahrenheit hydrometer is a constant-volume device that will float in water. In the figure shown here, the hydrometer is floating vertically in a cylinder containing a liquid. At the bottom of the hydrometer is a weighted bulb and at the top is a pan for small weights. To use the hydrometer, one first accurately determines its weight (W) while it is dry. Next, the device is placed in water, and a weight (w) sufficient to sink a marked point on the rod to the water-line is placed on the pan. At that point, the weight of water displaced by the instrument equals W + w. The hydrometer is then removed, wiped dry, and placed in the liquid whose density is to be determined. A weight (x) sufficient to sink the hydrometer to the same marked point is placed in the pan. The density (D) of the second liquid is then given by D = (W + x) / (W + w).

The Fahrenheit hydrometer can be made of either glass or metal.

References

References

1. See page 170 of ''[https://books.google.com/books?id=1jYAAAAAYAAJ&dq=fahrenheit+hydrometer&pg=RA1-PA170 School Physics]'' by Elroy McKendree Avery, 1895, American Book Company, New York, from which much of this article is taken.