PHYSICAL CHEMISTRY 27 



and bases on the physical properties of proteins is quite different 

 from that stated in the Hofmeister series of ions, if these pro- 

 perties be compared at the same pH. Thus the amount of 

 swelUng of gelatine at pH = 3 is almost the same for nitric, 

 hydrochloric, trichloracetic, phosphoric, and oxalic acids. 

 Sulphuric acid, however, gives, as is expected, one-half the 

 effect. 



Boundary Lubrication. — W. B. Hardy {Proc. Roy. Soc, 1921, 

 A 100, 550) has examined the lubricating properties of the 

 aliphatic hydrocarbons, acids, and alcohols. In the case of 

 volatile substances it was possible to admit the substance to 

 the slider and plane surface in the form of vapour mixed with 

 air, and to determine the effect of varying the concentration in 

 the vapour state on the lubricating properties. Below certain 

 concentrations of vapour, the amounts of adsorbed lubricant 

 were insufficient to produce any change in the static friction 

 between the clean surfaces of the slider and the plane surface. 

 As the concentration in the vapour state increases above these 

 limits, the static friction decreases down to a constant value, 

 which is independent of further additions of lubricant even to 

 flooding. 



ORGANIC CHEMISTRY. By O. L. Brady, D.Sc. F.I.C. University 

 College, London. 



The Free Ammonium Radical. — ^The discovery of the diaryl 

 nitrogens has revived interest in the isolation of the ammonium 

 radical. Schlubachand Ballauf (5er., 1 921, 54, 281 1) continuing 

 the work of the former {Ber., 1920, 53, 1689) have electrolysed 

 solutions of tetraethylammonium iodide in liquid ammonia at 

 — 70°. A deep blue solution forms round the cathode, which 

 solution is immediately decolorised by iodine with the formation 

 of tetraethylammonium iodide and reacts with sulphur and with 

 dimethyl pyrone. The blue solution gradually becomes colour- 

 less when kept at low temperatures, but still retains its 

 reactivity. The reactive colourless solution is best obtained, 

 however, by allowing a slight excess of tetraethylammonium 

 chloride to react for twenty-four hours with a solution of 

 potassium in liquid ammonia at — 70°. The authors suggest 

 that the blue solution contains tetraethylammonium N(C2H5)4 

 and the colourless reactive solution the associated compound 

 [N(C2H5)J2. Weitz, Roth and Nelken {Ann., 1921, 425, 161) 

 by the action of zinc dust on a mixture of pyridine and ben- 

 zoylchloride have isolated a brown crystalline compound which 

 has the composition CigHioON to which they give the name 

 benzoyl pyridinium and formulate as (i), though they consider 

 that it can react as (ii) ori(iii) : 



