Mechanochemical reactions that take place when milling and pressing analytes with KBr to form a disk suitable for IR spectral work are reviewed. The topic is extended to other alkali halides matrices. The literature from 1952 is surveyed from an analytical point of view. Several reactions are discussed at length with emphasis on the nature of the products. The mechanism and the factors affecting the mechanochemical changes are discussed in detail for copper sulphate, alkaline and transition metal ferricyanides, and Ag, Hg and Pb salts.