Inexpensive Gouy Balances Like the author of "An Inexpensive Gouy Balance for Magnetic Susceptibility Determination'' (Viswanndham, P., J. CHEM. EDUC., 55,54 (1978)j I have also found that a simply constructed Gouy balance gives surprisingly good results. In contrast to the rewrted svstem. , .I used a trinle-beam balance and simnlv . , removed the o m . No hole had to be drilled throueh the lwwcdthe balil& since the section d i r e h y 1,elow the heam isopm.The tahlr i w c i a a \ a phgc1c5lahornrc,rs rnlrleuhirh already has holes drilled through rt. Thus. thp sample could be suspended from n nylon ~ o r du,h~rhpsw:d t h n u ~ hthe llule in the rnhlr and wnsntwchrd to the h ~ nmmally k ~ s r 10 d hdd the hnlante pan. A n inrxpcu,ivr 5 rr. pwmnnent m n s r t was positioned on the floor beneath the table. Another adaptation was the use of a laser "optical lever" for measurement of the effect of the magnetic field on the sample. A small mirror ( 1em2) was fastened onto the beamofthe balance and an inexpensive neon laser (Metrologic),also commonly available in physics laboratories, was positioned a t a distance of about 5 ft in such a way that the laser beam reflected from the mirror onto a wall. As the magnet was moved in and out of the vicinity of the sample, the laser beam projected onto the wall showed dramatic vertical movement. sured. The students were given a number of materials of known susceptibility, and they were then able to generate a goad value for the calibration constant ((3) relating susceptibility to the vertical displacement of the laser beam. This value of (3 was used to determine the susceptibility of an unknown material. The value of this experiment lies in its ability t o dramatize differences in the behavior of diamagnetic and paramagnetic materials in magnetic fields. As a bonus, this relatively simple equipment generates remarkably accurate magnetic measurements. Saint Mary's College Notre Dame. I N 46556
550 1 Journal of Chemical Education
Margaret A. Cavanaugh
