1883.] Molecular Weights of the Substituted Ammonias. 347 



electrostatic to the electromagnetic measure of the capacity is v 2 . 

 The result of the experiments, using Lord Rayleigh's value of the 

 ohm, was that 



" v "=2-963 x 10 10 in C.G.S units. 



XI. " On the Molecular Weights of the Substituted Ammonias. 

 No. I. Triethylamine." By James Dewar, M.A., F.R.S., 

 Jacksonian Professor, Cambridge, and Alexander Scott, 

 M.A., D.Sc. Received June 21, 1883. 



The conduct of the experiments relating to a new determination of 

 the atomic weight of manganese recently communicated to the Society* 

 has led us to prosecute some further studies in this field of research. 

 The following note deals with the preliminary results arrived at re- 

 garding the molecular weight of a member of a class of bodies which, 

 strange to say, have not been previously selected for accurate determi- 

 nations of this kind. The substituted ammonias are peculiarly fitted to 

 reveal the effect of small differences from whole numbers in the con- 

 joint values of the atomic weights of carbon and hydrogen. By selecting 

 tertiary amines of high molecular weight it is possible to integrate 

 these small positive or negative increments through the increase in the 

 number of carbon and hydrogen atoms in the substituting radical. There 

 is also a special advantage in employing the fully saturated ammonium 

 derivatives for experiment. Theoretically it ought to be possible to 

 ascertain by this method whether the atomic weight of hydrogen 

 differs from unity, provided the atomic weight of carbon be accepted 

 as sufficiently well defined, from other methods of investigation. The 

 difficulty of getting perfectly pure substances for such work, together 

 with the hygroscopic character of the ammonium compounds, introduces 

 serious difficulties, and for the purpose of testing the accuracy of the 

 proposed method, the preliminary experiments have been made with 

 triethylamine. 



The triethylamine employed was made by the action of chloride of 

 ethyl on ammonia, and was transformed into the bromide of tetraethyl- 

 ammonium. This bromide of the fully substituted ammonium was 

 decomposed by dry distillation into triethylamine and bromide of 

 ethyl, and the base separated in the form of the chloride. The free 

 base was separated from the chloride with caustic potash, and after 

 careful drying with anhydrous oxide of potassium was subjected 

 to fractional distillation. The portion boiling between 90° and 91° 

 was converted into the hydrobromate and its equivalent relation to 



* " On the Atomic Weight of Manganese," " Proc. Roy. Soc.," vol. 35, p. 44. 



