An Easily-Constructed Rhombohedron Model A model of a rhombohedron-necessary
fur teaching stereochemistry (especially of inorganic compounds)-can made easily by using a sealed empty envelope. T h e steps (dlustrated in the figure) are given below.
he
1) T h e envelope is folded down the center lengthwise. 2) T h e lower part uf the envelope is folded up so that corner B Salk on the center line. T h e new corner on the right-hand side of the envelope is marked C. 3) This lower part is folded further along line A B so that point C falls an the left-hand side of the envelope. T h a t point is marked D . T h e new corner on the upper part of the right-hand side of t h e envelope is marked E. 4) T h e horizontal line E F , perpendicular to the right-hand side of the envelope a t E , is drawn, along which the upper part of the envelope is cut off. 5) T h e remaining portion is flattened out and its lower part is folded u p a t point D so that corner A falls on point C. T h e new left end of the base is marked G . 6) T h e upper part of the envelope is folded down a t point C so that corner E falls on point D. The new upper right corner is marked H . 7) T h e envelope is Solded both backward and forward along lines AE, D H , GC, DG, and HC. 8 ) T h e intersection of the lines A E and DG and that of the lines AE and HC are marked I and J , respectively. 9) Cut the envelope along the lines GI and H J . 10) Separate the front of the envelope from the back by cutting the base A R along the lines G A and BG. 11) On the back of the envelope, points corresponding to G , H , I , and J , are marked G * , H * , I*,and J*, respectively. 12). Ohliaue lines are drawn to shade six equilateral trianrles (IAG a n d H J E on the front, I*AG* and H*J*E on the back, and and HH*D on both sides).' 13) T h e front of the envelope is cut along lines GC and HD. 14) T h e right- and left-hand sides of the envelope are pushed toward each other so that lines IC, CI*, and 11' form a n equilateral triangle. 15) Points A , G , and G' are pressed together and the shaded triangles ( I A G ,I*AG*, and CGG*) are folded inside. T h e ~~
EGG*
References Yamana. S.. i.
