Most crude oils contain asphaltic substances that may be naturally orartificially precipitated. In the Greeley field, California, this asphalticbitumen is precipitated during the flow of the oil from the reservoir to thestock tank. The mechanism of such precipitation is not well understood. Thispaper presents the progress that has been made by using the electron microscopeas a new tool and by observing the effects of the streaming potential on theformation of bitumen particles. Crude oils at atmospheric pressure viewed in the electron microscope in verythin films under a vacuum showed no asphaltic particles. A technique ofpreparing slides of thin films by dilution of the oil with benzene and washingin petroleum ether was used at first, and these observations showed that thesolvents caused the formation of the particles, varying from 0.01 to 0.2 micronin diameter. The electrical effects of fluids flowing through porous solid were studied, with emphasis on the formation of colloidal particles by the streamingpotential. The streaming potential of crude oil flowing through sand wasmeasured and was shown to be responsible for the formation of bitumenparticles. These results bring out a new phenomenon, which may occur when crudeoil flows through the porous oil reservoir. 1. The Electron Microscope as a New Tool Asphaltic particles have been precipitated from crude oils by a variety ofmechanisms. Asphalt has been the subject of widespread investigation but, owingto the complexity of the substances being considered, progress has been slow.Investigators working primarily with the asphaltic substances have treated thesubject from the colloidal standpoint and have developed theories that picturethe asphaltic particles as surrounded by adsorbed materials. Thedeasphaltization of lubricating oil by the use of solvents treats the subjectprimarily from the standpoint of liquid-liquid equilibria. A completeunderstanding of asphaltic substances would make possible the following of thematerial from its initial state in the crude oil through precipitationprocesses to the final plastic stage, the most common form of which is used inasphaltic pavements. T.P. 1514