C. E. Linebarger — Nature of Colloid Solutions. 223 



it to be 0"1°, which corresponds to a molecular mass of 456, a 

 number upon which no weight can be laid, as doubtless most 

 of the depression was clue to the salt present in the solution.* 

 The presence of a small amount of salt would have no effect, 

 however, upon the osmotic pressure, since the salt could pass 

 freely through the membrane. Osmotic pressure is then due 

 to the colloid alone. The delicacy of the osmotic pressure 

 method is very great. Using the solution itself to measure the 

 pressure, a molecule 2000 times heavier than hydrogen in 1 per 

 cent solution would support a column more than a yard high. 



A colloid solution might be regarded as a step between a 

 true solution and a true emulsion. The colloid molecule is so 

 much larger than the water molecule that it stands to reason 

 that the properties of colloid solutions must differ markedly 

 from solutions of substances which possess a molecule but sev- 

 eral times heavier than water. Hence diffusion of colloids 

 takes place slowly; the osmotic pressure is small ; and but a 

 slight lowering of the freezing point and raising of the boiling 

 point occurs. 



As to the nature of this large molecule and how the simple 

 molecules are combined to form the complex molecules, it is 

 hard to give an opinion. The ease with which colloidal 

 substances are coagulated, i. e., pass into the solid state, indi- 

 cates that there exist in the solution molecular groupings simi- 

 lar to those existing in a solid. It is generally admitted that 

 in solids the simple molecules unite to form more complex 

 molecules or " tagmas." Similar " tagmas" might exist as such 

 in the solution. 



The facts are that solutions of colloids have a definite rate of 

 diffusion and. exert a definite osmotic pressure. As osmotic 

 pressure, diffusion, lowering of the freezing point and raising 

 of the boiling point are intimately related, we can say that col- 

 loid solutions also have freezing and boiling points differing 

 from those of the solvent. We conclude then that a colloid 

 solution is a solution in the ordinary acceptation of the term 

 and. not a "suspension." 



I am occupied in making determinations of the osmotic pres- 

 sure of colloid substances, especially of the albuminoids. Cer- 

 tain albuminoids, as is well known, are insoluble in pure water, 

 but quite soluble in a solution containing a little of some salt. 

 As this salt does not affect the osmotic pressure in the least, its 

 presence does no harm. Thus I hope to get more of an insight 

 into the nature of the complex substances of animal origin. 



Clark University, Worcester, Mass. 



* I might have determined the amount of salt present and thus easily found 

 what depression was due to the acid alone ; but as the depression was so small 

 and the solution so dilute, the results would have been worthless. 



