A STUDENT-MADE CHEMICAL BALANCE OTTO J. WALRATH High School, Bloomfield, New Jersey
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ANY a high-school chemistry student wants to have his own chemical laboratory a t home. One of his difEculties, especially if money is scarce, is to get a suitable balance. The following accompanying drawing and description of a balance made by one of our boys last year should be of interest to teachers who desire projects for their students. I t can easily be made in the manual-training shop and the cost is very small. Moreover, its accuracy will prove to be much greater than that of some balances found in high-school laboratories.
The long strip is bent ll/p" from each end. The first two strips are then soldered 1"apart between the bends of the long strip. Now, V-shaped notches are made from the ends of the shorter strips. Of course, these are on the upper side. At the center of these strips (on the lower side) V-shaped notches are made. These will rest on the pivot D. Great care should be taken that they are uniform for both strips. The weighing pans are of aluminum trimmed to the same weight. They are held by hrass crosses, whose ends extend just beyond the pans. The pan pivots F are ground from hack-saw blades a/8" X 1a/8R.Two steel wires are now securely soldered near the ends of the pan pivots. These wires should be about six inches long. It is best, before proceeding farther, to have the lever supported at both ends in a horizontal position. The pan pivots can then be placed in position and the free ends securely soldered to the ends of the crosses so that the cross will be in a true horizontal plane. It is important to use great care in getting the crosses exactly parallel to the lever. Four steel wires may be used but it is easier with two to get the pans on and off the crosses. The slides, made of gage brass, wide and long enough to bend (above and below) around the longer arm, can next be placed in position a t the extreme left of the long strip. In bending the slide make sure it is able to move freely to the right or left without being too loose. The lever is now ready to place on its support. The brass slide a t the left will make that arm slightly heavier than the right. A brass counterweight is now clamped over the back strip a t the right of the center pivot and moved until the whole lever is level. The counterweight is then tightened in position. After the above adjustments, l'/s" wood cubes are placed on the base directly under the pans, to prevent The base A is made of wood 14" X 6" X 3/n". At the exact center is fitted an upright C of wood the pans from swinging too far. 3" X ll/&"X 5/8''. The latter is fastened by brass The gram divisions on the scale are determined by angles to the base. Two brass strips (0 8" X '/sf' experimentation, the zero point being where the scale ('/la" gage) are attached to the upright and these balances with the slide placed a t the extreme left. extend 5" above its top. V-shaped notches are made The 10-gram point can be found by balancing against in the exact middle of the upper ends of the brass strips a 10-gram weight. The space between 0 and 10 may to hold the center pivot D, which is ground from a hack- now he divided into equal parts and these again into saw blade and which is soldered in place in the above tenths. notches. Finally, a stout steel wire is soldered to the hack The lever proper is made of two hrass strips H of E in line with a marking lengthwise though the gage) and one strip E of the same center of the front brass strip on the support. This 10'/2" X gage). This latter strip will serve as an indicator and will also aid in leveling material 13'/%" X will later carry the slide and have the gram markings. the scale. 118
