324 SECTIONAL TRANSACTIONS.— A. 



Dr. M. Mathieu. — The X-ray cinematography of a simple fibre re- 

 action. 



Cellulose fibres are transformed into trinitro-cellulose when exposed to 

 gaseous nitrogen pentoxide at ordinary temperature. By using an X-ray 

 tube with rotating anticathode it is possible to take diffraction photographs 

 of such fibres every two minutes or so, since an exposure of one minute is 

 sufficient for each photograph, and so to follow easily the evolution of the 

 new structure. 



The regularity of the original structure first gradually disappears in the 

 direction of the fibre-axis, until a stage is reached when there remain only 

 equatorial reflections and the pseudo-period corresponding to the length 

 (5-2 A.) of a glucose residue. The molecular chains then move further 

 apart and slide over one another so as to leave the effective residue thickness 

 unaltered, whereupon the (101) reflection of nitro-cellulose appears. After 

 this, little by little, the molecular chains fold and take up their stable 

 configuration, and the fibre period of 25*1 A., which characterises trinitro- 

 cellulose, can be observed. 



The whole process is completed in an hour and serves as a simple and 

 striking example of how physical and chemical transformations can now be 

 followed in detail with the aid of a powerful X-ray tube. 



Dr. J. Speakman. — Some chemical aspects of the elastic properties of 

 the keratins. 



The keratins consist of parallel peptide chains bridged by cystine and salt 

 linkages, and the configuration adopted by the structure under any circum- 

 stances represents a balance between the tendency of the peptide chains to 

 fold into six-membered rings and the resistance to folding offered by the side 

 linkages. The reactivity of these side linkages depends on their state of 

 strain, which, in turn, depends on the configuration of the structure. In 

 consequence, the properties of each type of linkage in keratin influence 

 those of the remainder. For example, the reactivity of the cystine linkage 

 in strained fibres is frequently at a maximum under conditions where the 

 salt linkages are most stable. Similarly, the elastic properties of chemically 

 modified fibres present many features of unusual interest. 



Dr. E. Griffiths, F.R.S., and Mr. J. H. Awbery. — Apparatus for 

 maintaining constant humidity. 



The need for maintaining constant humidity is experienced in many 

 industrial processes, such as paper making, textile spinning and weaving, 

 as well as in the laboratory. 



Two forms of apparatus suitable for laboratory work have been devised, 

 one for supplying a stream of air at constant humidity, and the other for 

 maintaining the atmosphere in a chamber at a fixed humidity. 



In both forms, the result is attained by mixing dry and moist (nearly 

 saturated) air in suitable proportions. This method has many advantages 

 over the methods in which salts or solutions are used to attain the desired 

 humidity directly. 



In the apparatus for providing a stream of air at known humidity, air is 

 drawn through the apparatus, and branches into two streams, each pro- 

 vided with a flowmeter. One stream passes through water towers, and the 

 other over silica gel. The streams are then reunited, a dew-point hygro- 

 meter being inserted in the combined stream. 



The advantage of the type of controlled chamber now described is that 



