The Atlantir Refining Co., Philadelphia, Pa.This study of the crystal types of pure hrdrocarbons was undertaken to secure data for application to wax processing, and to determine why a paraffin wax niay form three different types of crystals-needles, plates, and malcrystalline masses.Twenty-three pure hydrocarbons comprising paraffinic, naphthenic, and aromatic compounds in the molecular weight range of paraffin wax were obtained from il.P.1. Project 42. These pure hydrocarbons were crystallized from the melt a t different rates and from solutions of ethyl acetate and nitrobenzene a t different rates and over a wide range of temperatures. Crystals of each pure hydrocarbon except n-hexacosane were prepared in each of three predominating types: plates, needles, and nialcrystalline masses. Needle crystals could be obtained from n-hexacosane only by the additinn of small amounts of HE crystallization of paraffin waxes as needles, plates, and T malcrystalline masses has been the subject of many studies.Various theories have been advanced to explain why a paraffin wax may form these three different types of crystals. This paper presents data which reconcile differences in the theories.This study of the crystal types of pure hydrocarbons was undertaken in order to secure accurate fundamental data for application to wax processing.Twenty-three pure hydrocarbons comprising paraffinic, naphthenic, and aromatic compounds in the paraffin wax molecular weight range were obtained from A.P.I. Project 42. These pure hydrocarbons were crystallized from the melt and from solution under widely different conditions.The study of these pure hydrocarbon crystals included: the size and external shape of the crystals, the factors which influence the type of crystal formed, the optical properties and crystal systems of the crystals, and the similarity of the pure hydrocarbon crystals to paraffin wax crystals.The shape and size of wax crystals have long been studied. The microscopist refers to the external shape of a crystal as its crystal habit. The two crystal habits which are most frequently observed for paraffin waxes are plates and needles. Plates are found in pressable wax distillates and in refined waxes (8).Needles are found in sweatable slack waxes.A wax distillate is the fraction of a crude petroleum which contains the paraffin wax. To separate the paraffin wax from the oil, the wax distillate may be chilled until the wax crystallizes and the resultant slurry may be filter pressed. If the wax forms a filter cake from which the oil drains easily the wax distillate is pressable. If the oil cannot be separated well from the wax crystals in the pressing operation, the wax distillate is unpressable.The slack wax is melted and charged into the sweat ovens where the wax is chilled to solidify it somewhat and then it is slowly heated. If oil and low melting waxes drain away from the slack wax during the sweating operation and leave a high yield of wax with low oil content, the slack wax is sweatable. If a wax of low oil contentThe wax le...