191 1] Walter H. Eddy 83 



electolytes influenced the pressure to a remarkable extent. His 

 work has been confirmed by others. While granting therefore, a 

 degree of osmotic pressure to colloids, the influence o£ other fac- 

 tors is so great as to show the futiHty of trying to calculate molec- 

 ular weights by this method. There is also still much controversy 

 as to how electrolytes influence osmotic pressure. Robertson claims 

 that proteins exist as ion proteins ; that the contained salts are not 

 impurities but rather parts of the normal protein molecule. In that 

 event purification may be actually cleavage and may carry us 

 too far. 



The ultramicroscope has thrown some light on the question of 

 whether protein Solutions are suspensions or Solutions. With it we 

 can detect particles of 4 X lO"^ mm. diameter or ten times the 

 estimated size of ordinary chemical molecules. The great majority 

 of protein Solutions show, with this Instrument, visible particles, 

 tending to confirm the idea of Suspension. It is not certain, how- 

 ever, that these are not molecules. Lindner and Picton have shown 

 by the study of colloidal Solutions of arsenious sulfide that there is 

 no hard and fast line to be drawn between colloidal Solutions and 

 crystalloidal Solutions. They find that arsenious sulfide Solutions 

 may exist in four states : 



1. Aggregations visible under the ultramicroscope. 



2. Free from visible particles, but indiffusible. 



3. Containing invisible particles which diffuse but are retained 

 by a porous cup. 



4. Containing invisible particles which diffuse, pass through 



a porous cup but scatter the light. 



We have here a substance of relatively simple chemical character 

 exhibiting every characteristic of Suspension, colloidal Solution and 

 crystalloidal Solution. 



Investigation of the Brownian movement has shown that it is 

 probably merely a phase of molecular energy slowed down by the 

 size of the aggregate. 



In short we do not know whether to regard a given protein 

 Solution as a true Solution of large molecules, or as a Suspension ; 

 as contaminated by salts, or as holding them wholly in molecular 

 combination. We are, however, justified in looking forward to 



