Chemistry and Physics. 395 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Blue Color of Basic Lanthanum Acetate and Iodine. 

 — The very remarkable reaction, similar to that of starch, which 

 basic lanthanum acetate gives with free iodine was observed by 

 Damour in 1857, and has been frequently applied for the qualita- 

 tive detection of the rare earth. The reaction has been studied 

 recently by W. Biltz, who finds that it does not take place when 

 the nitrate is used, and that it is dependent to a large degree 

 upon the physical condition of the precipitate, which should 

 possess the semi-transparent appearance of a colloidal substance. 

 A product that is more pulverulent and white, such as is usually 

 obtained from boiling acetate solutions, gives only a brown 

 color with iodine. After the blue product is once formed, how- 

 ever, the liquid in which it is suspended may be heated to a higher 

 temperature without injury to the color. An addition of indif- 

 ferent electrolytes, such as potassium nitrate, is also without 

 injurious action, so that the reaction may be obtained from solu- 

 tions of lanthanum nitrate which have been acidified with acetic 

 acid before precipitation. The reaction always appears with 

 certainty when a solution of iodine in potassium iodide is added 

 to a lanthanum acetate solution, and then enough ammonia is 

 added cautiously, so that the brownish yellow color of iodine 

 does not quite disappear, and finally the liquid is heated very 

 gently. A dark blue precipitate gradually forms, or, if the solu- 

 tion is very dilute, a blue colored liquid is obtained. Quantita- 

 tive experiments showed that the amount of iodine taken up by 

 the precipitate is very nearly proportional to total amount pres- 

 ent in the liquid ; hence the conclusion is reached that the phe- 

 nomenon, like the formation of iodized starch, is one of adsorp- 

 tion, and that the blue substance is not a definite compound. — 

 Berichte, xxxvii, 719. h. l. w. 



2. Yellow Antimony. — It has been known for many years that 

 an unstable, yellow form of arsenic exists, which is analogous to 

 yellow phosphorus. Stock and Guttmann have now succeeded 

 in preparing a yellow modification of antimony by the action of 

 air or oxygen upon liquid hydrogen antimonide at — 90°. The 

 substance is spontaneously transformed into the black form even 

 more readily than yellow arsenic ; for the change takes place in 

 a few seconds even at —50°, and even at the temperature of its 

 formation, —90°, it is so unstable as to become brownish or 

 blackish in a few hours. The oxidation of hydrogen antimonide 

 at the low temperature used for the preparation of the substance 

 is very slow, so that the yield is small. It was shown that the 

 yellow substance does not contain hydrogen, and that it is solu- 

 ble in carbon bisulphide at a temperature somewhat higher than 

 — 90°, giving a strong yellow color to the solution. Imme- 



