A. G. Pinkus and P. G. Waldrep
Baylor university Waco ,Texas
Inexpensive and Convenient Method for Powdering Solids for Melting Point Determinations
Recently, a new mulling technique for preparing samples for infrared spectra was reported which makes use of ground glass plates.' This technique proves to be very satisfactory in powdering solids for melting point determinations in the elementary organic laboratory. The use of ground glass plates has many advantages over methods now commonly used. There is not the danger of breakage of thin watch glasses with the glass rod or spatula used. Since the surface of a watch glass or a porcelain dish is curved, crushing with a flat spatulaor knife blade is difficult. No other utensils are required but the two glass plates, and powdering is fast, simple, and complete. Paper is not suitable for hard crystals; there is also the possibility of contamination with paper fibers. Clay plates
61 8
/ Journal of Chemical Education
areporousandmay absorb some of the compound; or clay particles may become mixed with the organic powder, making observation of the completion of melting more difficult. Cleaning of the glass plates is very simple, i.e., by washing with an organic solvent or by mulliug with sodium carbonate followed by rinsing under the tap as suggested in the original paper. The glass plates are very inexpensive, i.e., several are equivalent to the cost of a mortar or a spatula. The process of grinding the plates using 220 mesh carborundum (used in the original reference) is very simple and can he performed by the student. The plates are merely rubbed together with moistened carhorundum powder between them. usine a rotarv motion. -
' CROOK,A., A N D TAYLOR, P. J., C h a . & I d . , f958,95.
