RECENT ADVANCES IN SCIENCE 637 



when treated with sulphur is not confined to natural caout- 

 chouc but should be regarded rather as a state of matter 

 acquired by some amorphous substances of high molecular 

 weight which are called by the author " resinoids." The 

 elastic state is only able to persist within certain temperature 

 intervals ; thus caoutchouc loses its elastic properties when 

 cooled to — 20 C. and becomes leathery. The temperature 

 at which a substance acquires elastic properties is called the 

 11 temperature of elasticity," while the temperature at which 

 elastic properties are completely lost is called the " fatal 

 temperature." These two temperatures form two new char- 

 acteristic constants for resinoids, comparable with the melting- 

 point and boiling-point of a crystalline solid, and may be 

 employed for identifying or classifying caoutchoucs. These 

 temperatures may be determined in colloidal solutions, by means 

 of viscosity surface tension, or density measurements at various 

 temperatures, all three methods giving identical results. 



Attempts on the part of malingerers to simulate jaundice 

 by taking repeated small doses of picric acid have led to the 

 publication of three papers (/. Pharm. Chem. 191 5 [vii], 12, 

 228, 350 and 366) dealing with the detection of picric acid and 

 the methods employed in distinguishing between pathological 

 jaundice and the condition artificially induced by picric acid, 

 and there appears to be no difficulty in distinguishing between 

 the two conditions by analysis of the urine. 



In conclusion one other paper dealing with analysis may be 

 quoted. According to Vintilesco and Popesco (/. Pharm. 

 Chem. 191 5 [vii], 12, 318) the rancidity of a fat is due to the 

 absorption of oxygen which may be liberated by a peroxidase 

 and detected by tincture of guaiacum. To ascertain by 

 chemical means whether a given fat is rancid, 10 grams of 

 the sample are melted and shaken for one minute with 5 

 drops of diluted blood, 10 drops of tincture of guaiacum, and 

 10 c.c. of water. If the fat is rancid the resulting emulsion is 

 coloured blue. The reaction is given by rancid fats even after 

 they have been heated for a few minutes to 120 . 



GEOLOGY. By G. W. Tyrrell, A.R.C.Sc, F.G.S., University, Glasgow. 



Dynamical Geology. — The renewed discussion on coral-reefs is 

 continued by Prof. R. A. Daly, who elaborates in detail the 

 glacial-control theory of their origin proposed by himself in 1910 



