The colloidal nature of caoutchouc

510

ALBERT SAL VELR .

[J .

F. I.

much of its ductility because of the presence of troostite . This structure may be produced by quenching small pieces in oil, or larger ones in water, or by a suitable tempering of hardened pieces . The structure of mild steel containing ferrite, troostite, and sorbite is shown in Fig . u . In Fig, r, Diagram V, the steel has been cooled so quickly that some martensite, as well as troostite, remains undecomposed on reaching the bottom of the critical range, while but a very small amount of ferrite has had time to separate . In this ferritotroostito-martensitic condition the metal is hard and deficient in ductility . A structure of this type may be produced by quenching small pieces in water . The retention of martensite to the exclusion of troostite, and, a fortiori, the retention of austenite, is quite impossible in mild steel. While martensitic structures, moreover, are those needed in high carbon steel for the production of cutting tools, for instance, they are never wanted in low carbon steel, the structures depicted in Fig . T, Diagrams T, II, and III, being the only ones of interest to the users of such steel . Fig . 12 is a composite photo-micrograph showing the various types of structure mild steel may be made to acquire . The legend makes it self-explanatory . The Colloidal Nature of Caoutchouc . A, W-\'AGNER . (Cheni . xxxvi, 833 .)- .Ahrens's statement that the so-called Para-spots in pure vulcanized mixtures consist of an organic substance and not of crystallized sulphur is shown to be erroneous by the following experiment. When a thin section of pure vulcanized rubber is placed together with a solvent . such as benzol, between two glasses and examined under a microscope of comparatively low magnification, ramified, arborescent forms are seen, which are composed of small crystals ; there are also present small, round, floating bodies, which prove to be amorphous sulphur. After a short time this sulphur dissolves, and the spherical bodies as well as the arborescent forms gradually disappear : with carbon hisulphide as a solvent, solution is more rapid . This solution is clear except small fragments of foreign matter (filling, ctc .) . Thus the theory of the network structure of albuminoid compounds or of polymerized or oxidized rubber in vulcanized rubber appears untenable . Further proof of this is given by the fact that when vulcanized rubber containing no free sulphur is examined as above, the structure described is not visible-at any rate, not under such low magnification as is necessary for the identification of the different crystalline forms of free sulphur in rubber . Zeit .,

F. L, May, 1914-

.pfGi7UVJNCUS COAL

COAL AND 1Th Br-pmomcm



J. F . I ., May 1914 . ",Sle;RN

ecmsry,, H1.

%esozoiic

Tertiary

Coal fields ale shown thus: 6' = Paleoeoic

Coal fields of the world .

CURL AND ITS BI PRODUCT,