jolly balance

Main device, now largely obsolete, for determining the specific gravity (relative density) of solids and liquids. Invented by the 19th-century German physicist Philipp von Jolly, it consists in its usual form of a long, delicate, helical spring suspended by one end in front of a graduated scale. To the lower end of the spring is attached a weight pan and below that a small wire basket for samples. The difference in extension of the spring when the sample is suspended in air and in water represents the loss of weight in water; the weight in air divided by the loss of weight in water gives the specific gravity. The specific gravity of a liquid can be obtained by suspending any convenient specimen of a solid first in water and then in the liquid undergoing the test; the ratio of loss of weight of the solid in water and in the test liquid gives the specific gravity of the liquid. 1. Introduction The Simple Form Jolly Balance is used to • determine the density of solids and liquids using Archimedes’ principle • measure the surface tension of liquids • demonstrate simple harmonic motion • verify Hooke’s Law This versatile instrument is very popular in high school and college physics laboratories. 2. Description The instrument consists of a coil spring, two pans, a graduated metric scale mounted on a mirror, a beaker platform, and a support rod mounted on a base with leveling screws. The assembled apparatus is shown in Figure 1. The metric scale is graduated from 0 to 65cm in 1-millimeter divisions. The heights of the spring, suspended pans, and metric scale can be adjusted by repositioning the friction clamps on the support rod. The height of the beaker platform can be adjusted by means of a thumb screw on the support rod. The overall height of the instrument is 104cm (41 inches). 3. Assembly The Jolly Balance should be assembled as shown in Fig. 1. Screw the support rod firmly into the V- shaped base. Insert a leveling screw at the end of each leg of the base. Slide the platform assembly on the support rod and tighten the thumbscrew at a position about 11cm above the base. Slide the scale panel clamp onto the support rod by squeezing the ends of the clamp. Slip the end of the panel through the slot in the platform and release the ends of the clamp when the 59cm graduation on the scale reaches the platform level. In a similar fashion, slide the spring support arm on the support rod and clamp it a few centimeters below the top of the support rod. Loosen the knurled knob at the free end of the spring support arm, bend the straight length of wire of the spring around the machine screw, and tighten the knob. Suspend the upper pan from the hook at the free end of the spring, and the lower pan from the hook at the bottom of the upper pan. Set a level, such as the #88430 Torpedo Level, on the platform and level the instrument by adjusting the two leveling screws in the base. Straighten the cross wire above the upper pan. This wire, which serves as a scale pointer, must be parallel to the platform. BRUNTON COMPASS PARTS OF BRUNTON COMPASS