306 REPORTS ON THE STATE OF SCIENCE, ETC. 
The author concludes : ‘In addition to the factors such as the presence of 
suitable food materials, optimum temperature, p, and the like, the growth rate 
of micro-organisms is greatly influenced by the concentration at the bacterium 
surface of the various substances present. The surface concentrations may 
already be considerable, even when scarcely detectable amounts are present in 
the bulk of the medium. The conditions necessary for favouring high-surface 
concentrations are shown to depend on the action of the substance on the inter- 
facial surface tension. The magnitude of this action can in many cases be 
estimated by the effect of the solute on the air/liquid interface. Adsorption 
appears to be a chemical process, reaction occurring between reactive groups 
in the material adsorbed and the one (acceptors) in the micro-organism. Single- 
point reaction leads to a simple differentiation between acid and alkaline reactive 
groups, whilst multi-point action increases the selective nature of the reaction, 
which ultimately became entirely specific.’ 
(1V.) Industrial Applications of Wetting Power. By W. H. Nuttall, F.1.C. 
(The Ioco Rubber and Waterproofing Co., Ltd., Glasgow.) 
The ability of a liquid tc wet a solid surface—i.c. to give an even, continuous 
film over it—is dependent upon three surfaca tensions: the surface tension 
liquid/air (T,), the surface tension solid/air (Tz), and the interfacial tension 
liquid/solid (T,,,). For the liquid to wet, T, must be greater than T,+T, 5. 
The explanation of ‘ wetting ’ is, however, still obscure, and our views on the 
subject are in a state of transition, largely as the result of the work of Langmuir 
and Harkins on molecular orientation at interfaces. 
The industrial applications described are: Mineral separation by flotation, 
separation of bitumen from rock, cattle dips and horticultural medicaments, 
anti-dimming preparations, and lubrication. 
(V.) Colloids in Relation to the Manufacture of Inks. By C. A. Mitchell, 
M.A., F.1.C. 
This is a short paper, drawing attention to a little-discussed aspect of applied 
colloid chemistry. The ordinary writing inks of the present day consist of a 
more or less soluble tannate of iron, and, on exposure to air, there is a gradual 
change into a black colloidal tannate, which remains in suspension and imparts 
a dark colour tothe ink. The use of acids in the ‘ blue-black’ inks is explained. 
(VI.) The Manufacture of Artificial Silk in Relation te Collcid Chemistry. By 
Edward Wheeler, A.C.G.1., A.I.C. 
‘The four processes for the manufacture of artificial silk in use to-day are :— 
(a) Cuprammonium process (also known as Glanzstoff or Pauly process). 
(b) Nitrocellulose process (Chardonnet process). 
(c) Viscose process (invented by Cross and Bevan). 
(d) Cellulose acetate process.’ 
The bearing of colloid chemistry on each of these processes is discussed in 
relation to the raw materials used, the preparation of the solutions, the coagula- 
tion of the thread in spinning, and the after-treatment necessary in each case. 
The properties of artificial silk as a colloid system are then considered in relation 
to the requirements of the textile industry. 
