Permanent Structural Change Research Articles

Reaction mechanics of sodium methoxide treatment of lard

AbstractLard was treated at several temperatures with sodium methoxide catalyst. Samples were taken frequently during the course of the reaction and were subjected to measurements of glyceride distribution, especially the trisaturated triglyceride fraction, in terms of melting point, cooling curve, aniline point, and x‐ray diffraction pattern. The over‐all reaction could be broken down into several phases. Catalyst Formation. The sodium methoxide reacts with a fat to form an active catalyst. Infrared spectra show the formation ofbeta‐keto esters during the reaction, probably intermediates in the ester‐ester interchange. Crystal Modification. This phase is characterized by a complete and permanent change in crystal structure with a simultaneous loss of GS2U peak in the cooling curve. The GS3 content is only slightly increased from the original lard at this point. IV, etc. Interesterification. During these phases the fatty acids of the triglycerides approach random distribution. Intra‐esterification occurs simultaneously but at a different rate. These phases are distinguishable from each other by their apparent GS3 contents, which increase beyond that of phase II.

On the nature of embrittlement occurring while tempering a Ni-Cr alloy steel

Data are presented to show that embrittlement in a Ni-Cr alloy steel proceeds by one mechanism at 925°F and by a different mechanism at 1250°F. The embrittlement occurring at 925°F may be removed completely by reheating to higher temperatures for very short times and has no influence upon further embrittlement at 1250°F. The embrittlement occurring at 1250°F appears related to a permanent structural change which has a significant retarding influence upon subsequent development of embrittlement at 925°F. It is suggested that retrogression phenomena are not necessary to explain embrittlement; on the other hand, segregation of solute atoms to prior austenite and ferrite grain boundaries may provide a better explanation of the occurrence of the two modes of embrittlement.

Osteoporosis and epiphysial arrest in joint tuberculosis; an account of the histological changes in involved tissues.

Amputation or post-mortem specimens from eight cases of joint tuberculosis, with immobilisation changes in bone, have been studied by fine-detail slab radiographs and subsequent histological examination. The findings in three of these cases are presented in detail. The immobilisation changes take the form of a true osteoporosis, which is strikingly focal in nature. In the adult the sites of most marked involvement include the subcortical bone adjacent to articular surfaces and the bone in the neighbourhood of the obliterated epiphysial plates. Areas of permanent change in bone structure may result, although commencing "repair" is seen in the form of newly developed bone trabeculae in the osteoporotic areas. In one case, where immobilisation occurred at an early age, changes in the growing epiphysial plates were produced in addition to osteoporosis. This is correlated with the known susceptibility of growing epiphysial cartilage to a wide variety of damaging agents. Radiologically, it is important to discriminate between these immobilisation changes and the bone destruction which might be produced by extension of the tuberculous lesion itself.