A Cell for the Measurement of Cataphoresis of Ultramicroscopic Particles

In a recent publication Northrop t describes a convenient cell for microscopic cataphoresis measurements which can easily be made by cementing together microscopic slides. The writer has modified the cell so that it can be employed for measurements of cataphoresis of particles of ultramicroscopic size such as colloidal gold, etc. The modification consists in cementing slides in such a maimer as to make it possible for a strong beam of light to pass through the front edge of the cell. The diagrams in Fig. 1 show the construction of the cell. The slides are lettered alphabetically in the order in which they are cemented together by means of de Khotinsky cement. Slide d is perforated and is made from an ordinary thick slide which has a circular fiat depression in the middle. This depression is easily cut away by means of a glass cutter and one edge of the slide is then ground off, leaving a space of 1 ram. between the perforation and the edge. Construction of the Cell.--Slide b is cemented on top of Slide a, leaving about 1.5 cm. of Slide a exposed. Slide c comes on top of b, and then Slide d on top of Slide c, taking care that the ground edge of d coincides in the same vertical plane with the exposed edge of Slide a. The long front edge of the cell is ground smooth, and Slide e is cemented to it. On top of Slide e come the blocks f and g, leaving about 2 cm. of the middle portion of Slide e exposed. The ends of the cell are then ground smooth, the inside of the cell is cleaned by means of lens paper and acetone, and end-tubes are then cemented on. The end-tubes consist of two short pieces (4 to 5 cm. long) of thick-walled glass tubing, one end of which is widened and fiat-