392 - Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 

 I. Chemistry and Physics. 



1. An alleged Allotropic Form of Metallic Lead. — About five 

 years ago it was observed by H. Heller that compact metallic 

 lead, when placed in contact with acidified solutions of lead salts, 

 undergoes after a time a remarkable change, becoming filled with 

 cracks at first and finally falling to powder. It was concluded 

 that an allotropic form of lead was thus produced, similar to 

 the well-known change of ordinary tin into the grey modification. 

 This view was confirmed by Cohen and Helderman, who studied 

 the phenomenon by means of the dilatometer ; they believed that 

 no chemical reaction took place, and decided that the allotropic 

 form was more dense than ordinary lead. 



A. Thiel has now studied and discussed this matter very thor- 

 oughly, and has reached the conclusion in a very convincing way 

 that this is no case of allotropy at all, but a peculiar case of 

 chemical action. He finds that the action takes place only when 

 lead nitrate is present in the solution, and that a well-known 

 chemical reaction takes place, dissolving the lead with the forma- 

 tion of lead nitrite. The peculiar action throughout the mass 

 of the metal is explained by Thiel as due to the presence of a 

 more readily attacked eutectic existing between the original crys- 

 tals of the metallic lead. The arguments are very convincing, 

 and it appears that the powder is certainly not an allotropic form 

 of the metal. — Berichte, 73, 1052. h. l. w. 



2. The Estimation of small amounts of Iron as Thiocyanate. 

 — Richard Willstatter, in connection with the analysis of cer- 

 tain physiological preparations, where the amounts of iron to be 

 determined were often between 0.1 and 0.02 rag., has applied the 

 colorometric method using ammonium thiocyanate with hydro- 

 chloric acid. Although this method has been frequently used in 

 the past, the author has found that the previously described 

 methods of procedure could be much improved. He uses a far 

 larger excess of the thiocyanate than has been customary, thus 

 obtaining a much more intense color. The solution to be an- 

 alyzed is compared with a standard solution of known strength 

 by adding 0.5 to 1 cc. of each 0.5 cc. of concentrated hydro- 

 chloric acid, and then 40% solution of ammonium thiocyanate 

 sufficient to bring the volume to 50 cc. There are certain pre- 

 cautions to be taken in comparing the colors. The red color 

 gradually fades, evidently from the reduction of the ferric salt 

 by the thiocyanic acid, hence the colorimetric readings must be 

 made promptly. Another difficulty is the fact that the ammon- 

 ium thiocyanate usually contains a little iron and gives a reddish 

 solution, but the author has found that the 40% solution becomes 

 colorless by boiling it for a short time, and that it remains with- 

 out color after cooling. — Berichte, 53, 1152. h. l. w. 



3. Glucosane. — Gelis observed in 1860 that when glucose is 

 heated to 170° C it loses water and is converted into a brown, 



