38 Messrs. Gladstone and Hibbert on the Molecular 



such exactness that the second derived function may be repre- 

 sented, within the errors of observation, by a not too small 

 number of straight lines with practically arbitrary termina- 

 tions. The proof of this is furnished by the fact that Mr. 

 Pickering has deduced from the specific gravity quite different 

 hydrates (singular points) from Mendelejeff, and from the 

 electric conductivity quite different hydrates from Crompton. 

 Mr. Pickering closes as follows : " The conclusion is the 

 absolute rejection of any other than the hydrate theory" 

 (p. 8i>). Looked at from the mathematical point of view the 

 conclusion might well be the t( absolute rejection" of the 

 so-called theory of hydrates, at least in the form defended by 

 Mr. Pickering. 



V. On the Molecular Weight of Caoutchouc and other Colloid 

 Bodies. By J. H. Gladstone, Ph.D., F.E.S., and Walter 

 Hibbert, F.LC* 



DURING the last meeting of the British Association at 

 Bath, we gave a preliminary account of some attempts 

 to determine the molecular weights of caoutchouc and a few 

 other substances by Baoult's method. We have since re- 

 peated most of the experiments and largely extended the 

 inquiry, and it seems to us that the results have a certain 

 physical as well as chemical interest. 



It is evident that this method is the only one that offers 

 much hope of success in dealing with such substances as 

 caoutchouc, but it is open to question how far the method itself 

 is to be trusted for giving the correct molecular weight of 

 compounds of this description. Our confidence in it, how- 

 ever, was strengthened by the following experiments, made 

 on substances of the same ultimate composition (wC 30 H 16 ), 

 but of known molecular weight in the gaseous condition. 

 We also made experiments on one or two closely allied 

 bodies containing oxygen. 



The compounds were dissolved in benzene which had a 

 freezing-point of 5°'25 C, and the experiment was conducted 

 in the usual manner. Each degree of the thermometer 

 scale was divided into twentieths, and it was not difficult to 

 estimate to the hundredth of a degree. Successive observa- 

 tions of a freezing-point nearly always agreed to less than 

 0°'02. 



The following table gives s — in col. II. the recognized 

 molecular formula, in col. III. the strength of solution, in 



* Communicated by the Physical Society : read May 25, 1889. 



