Weight of Caoutchouc and other Colloid Bodies. 41 



The molecular weight of these known colloids, as determined 

 by Raoult's method, is very high and confirms the generaliza- 

 tion of Graham. 



Experiments have already been made upon the so-called 

 carbohydrates by this process by Messrs. H. T. Brown and 

 G. H. Morris*. They found that the sugars had a mole- 

 cular weight agreeing with the received formula, but the 

 noncrystallizable bodies like soluble starch &c. gave them 

 results suggestive of specially high molecular weight. 



We may also note that in some recent investigations by 

 C. Liideking, he found that the addition of colloids to water 

 makes no practical difference to the boiling-point, and in 

 every case lowers the vapour-pressure very slightly!. These 

 results all indicate the same general conclusion. 



Our experiments were extended by making an examination 

 of solutions of the colloidal hydrates of aluminium and iron. 

 They were prepared by dialysing solutions of the basic 

 chlorides, but, as is well known, a small proportion of the 

 salt must be retained in order to prevent coagulation. The 

 iron solutions contained almost exactly one molecule of 

 chloride to fifteen molecules of the hydrate. The first 

 aluminium solution contained one molecule of the chloride to 

 five or six of the hydrate, the second one of chloride to nearly 

 ten of the hydrate. 



Substance. 



Weight in 100 

 grams of Solvent. 



Depression. 



Molecular Weight . 

 T=47. 



Ferric Hydrate 



>> 

 Aluminic Hydrate. . . 



19 



116 

 2-60 

 0523 

 1-37 



About 0-01 

 0025 

 0-060 

 006 



5452 



4888 

 409-6 

 1073 



The figures here given for the molecular weights of the 

 hydrates are calculated as if the whole depression were due 

 to the hydrate in solution, but the chloride present must have 

 exercised a considerable influence, especially in the first 

 aluminium solution. If allowance be made for this, the 

 molecular weights found would be higher than those given in 



* Chem. Soc. Journ. 1888. 



t Ann. Phys. Chem. [2] xxxv. pp. 552-557. 



