The electrophoresis of protein sols the presence of gold sols— albumen, gelatin and casein

Investigations of the changes in the electrophoretic velocities of proteins brought about by changes ofp H have already given material assistance in elucidating the electrochemical characters of these compounds, while the characteristic behaviour of each individual type offers possibilities of separating them in a delicate manner with the minimum of injury to their chemical structures. The behaviour of metal sols in the presence of proteins has furnished information as to the nature of each and has found application in the diagnosis of cerebro-spinal fluid and serum. The present work deals with solutions containing both proteins and gold sols. Two methods have been applied to the determination of electrophoretic velocities in an electric field; the observation under the microscope of the motion of particles in a small cell, and the measurement, on a scale, of the motion of a boundary. These methods have been called the micro- and the macro- methods respectively. A comparison of the concordance among themselves of the results obtained by each makes us disinclined to agree with the statement that the micro- is the more exact. Experience has shown that it is subject to numerous corrections on account of the difficulty of distinguishing between electrophoresis and electrosmose. Also its scope is limited since it is not applicable to proteins which are dissolved, or highly hydrated. For example, albumen has to be previously coagulated or deposited on particles of quartz or collodion (below). Loeb considers, however, that pure egg albumen, coated on collodion, behaves like denatured egg albumen. The observations of Ramsden tend to show that albumen is denatured when forming a film, and in confirmation of this one of us has observed that insoluble albumen forms at a toluene, albumen interface. The macro- method, on the other hand, is applicable to hydrophilic colloids in their original state, or very nearly so. It clearly possesses an easier technique, and is therefore more suitable for general testing. It has, of course, its own special difficulties, which are mentioned below.