 The empirical formula of Nujol is hard to determine exactly because it is a mixture but it is essentially the alkane formula where "n" is very large.To obtain an IR spectrum of a solid, a sample is combined with Nujol in a mortar and pestle or some other device to make a mull (a very thick suspension), and is usually sandwiched between potassium- or sodium chloride plates before being placed in the spectrometer.For very reactive samples, the layer of Nujol can provide a protective coating, preventing sample decomposition during acquisition of the IR spectrum.