Puligandla Viswanadham Ohio Dominican College Columbus. Ohio 43219
An Inexpensive Gouy Balance for Magnetic Susceptibility Determination
I n m a n y a school a n d college d o u b l e p a n e q u a l a r m balances a r e b e c o m i n g obsolete a n d a r e being r a p i d l y replaced b y a u t o m a t i c a n d s e m i a u t o m a t i c single p a n balances a n d digital balances. I n s t e a d o f discarding, a d o u b l e p a n balance, in conjunction w i t h a p e r m a n e n t m a g n e t , c a n b e converted i n t o a G o u y balance. T h e s t u d e n t i s i n t r o d u c e d t o t h e principles a n d o p e r a t i o n of a d o u b l e p a n balance' a n d m a g n e t i c p r o p e r t i e s of materials%imultaneously t h r o u g h a single experiment. A wooden desk (107 X 66 X 76 cm) is converted into the magnet housing by covering the three sides with 3-mm thick plywood. The fourth side is provided with a plywood d o w that can he opened or closed a t will hy sliding it on guide s h t s . A6-mm diam hole is drilled on the desk top to introduce thesuspension system into the magnetic field. 'The magnet is an already available Master Magnet No. 59 X 64 supplied by Camhosa, Scientific Company, Brightm Station, Mass. T h e magnet has pole faces of -30 mm and a pole gap o f i h o u t the same dimensions. T h e magnet has a flux density of 3000 Gauss. A magnet of similar flux density and variahle pole gap is obtainable from Edmund Scientific Company (Cat. No. 70,810) for under $60. The magnet is mounted o n the foot rest of the desk with a 102-mm door hinge wr t h a t the position of the magnet can be varied to facilitate weighing o f t h e sample in and out of field. Only minor alterations are made t o the rhainmnatic halance. A 0.5-mm diam hole is drilled a t the center o f t h e left pan. 'The pan support for the left pan is diseonnected and a 6-mm diam hole is drilled into the base d t h e balance to insert the suspension system carrying the sample tuhe. The halance is mounted on the desk top such that the center of the left pan from
54 1 Journal o f Chemical Education
which the sample tuhe is suspended is directly above the center of the magnetic field. Thus, the sample tube when suspended will he located exactly between the poles of the magnet. The sample tuhe cmsists of an 80-mm long and 6-mm o.d. Pyrex tube the hottom 20 mm of which are sealed with a low melting alloy. The top of the tuhe is flared in such a manner that a harness can he attached. T h e tuhe is connected t o one end of a Nylon cord with a silver hook to facilitate easy removal of the tuhe for sample loading or cleaning. The other end of the cord is passed through the hales in the desk top, halanee base, and pan, and is f'asteried with a knot. Students are directed t o weigh the samples by the rest point method, determine the magnetic susceptihility. and calculate the numher of unpaired electrons in the molecule. Magnetic susceptibilities of CuSO.vSHr0, Ni(NO:&, chrome alum, CoCI:,.6H20, and MnSOrHaO measured with this instrument were, respectively. 2.01, 3.13, 3.84, 4.98, and 5.92 RM and compare well with the expected values for these compounds.:' We have found t h a t this experiment is effective in elucidating the principles of operation of a double pan analytical halance and intmducing the student t o the magnetic properties of materials. With the availahilityof a desk and an analytical balance the cost ofconstruetion of a Gouy blanace is well under $100. and can be fahricated in a relatively short time.
'Evans, L., J. CHEM. EDUC., 32,419 (1955). 'Barnrw, G. M.. "Physical Chemistry," 2nd Ed., McGraw-Hill Book Ca., New York, 1966, p. 438. ."Figgis, 8. N., and Lewis, 3.. "Modern Coordination Chemistry," (Editors: Lewis, d., and Wilkins, R. J i , Interscience, New York, 1960, p. 406.
