Earlier researches on the transformations of terpineol with fused potassium hydrogen sulphate, aq. oxalic acid, sulphuric-acetic acid mixture and \(\gamma\)-alumina have been repeated, and in the reaction mixtures, α-terpinene, limonene and saturates have been quantitatively estimated. Reactions of terpineol, catalysed by iodine and boric acid, have been examined, and iodine has been found to be an excellent and quick agent for dehydrating terpineol. For eliminating α-terpinene in terpene mixtures, warming with maleic anhydride is shown to be a better route than agitating with cold Beckmann's chromic acid mixture. Bromination of terpinolene by Baeyer's technique has been improved, the essential change being the precipitation of the tetrabromide by addition of cold methanol. This modification avoids the Formation of oily products. No clean-cut elimination path for terpineol is revealed excepting in dehydrations with potassium hydrogen sulphate and alumina, wherein dl-limonene and terpinolene respectively are obtained as major reaction products. In all other cases, there result monocyclics containing α-terpinene, terpinolene, limonene and saturates including p-cymene, in varying proportions. A mechanism is proposed to account for the reaction products and to explain how terpineol can furnish both terpi­nolene and limonene with equal facility.