188 Scientific Intelligence. 



the size of the particles is very different in the various cases, and 

 that this depends upon the nature of the liquid employed. It 

 was especially interesting to find that it was possible to produce 

 solutions with particles of very small, uniform size which dis- 

 played the Brownian movements in a very lively manner. Fur- 

 ther study of this matter, which the author is undertaking, 

 promises to be of great interest, and he suggests that it may be 

 of importance in explaining the mechanism of common photo- 

 chemical reactions. — Perichte, xlii, 43*77. h. l. w. 



2. Potassium Percarbonate. — Much uncertainty has arisen in 

 regard to the true constitution of the product prepared in 1897 

 by Constam and von Hansen by the electrolysis of concentrated 

 potassium carbonate solutions to which the percarbonate formula, 

 K 2 C 2 6 , was ascribed by the discoverers. Up to the present time 

 this product has always been obtained in an impure condition, 

 containing carbonate, bicarbonate and water, and since it yields 

 hydrogen peroxide and potassium carbonate when dissolved in 

 water, it has been possible to regard it as potassium carbonate 

 with hydrogen peroxide of crystallization, instead of a true per- 

 carbonate. Moreover Tantar has obtained a well crystallized 

 product by the combination of sodium carbonate and hydrogen 

 peroxide, to which he gave the formula Na 2 C0 4 + YH 2 2 + H 2 0, 

 regarding it as a percarbonate combined with both hydrogen 

 peroxide and water. 



Riksenfeld and Reinhold have now succeeded in preparing 

 the electrolytic product in a nearly pure anhydrous condition by 

 the use of special precautions. The absence of hydrogen in this 

 preparation proved that it was not a hydrogen peroxide addition 

 product and analyses confirmed the formula K 2 C 2 6 . They have 

 also found a means tor distinguishing between percarbonate and 

 hydrogen peroxide in the fact that the former liberates iodine 

 immediately from a neutral potassium iodide solution, while 

 hydrogen peroxide acts only slowly upon such a solution. By 

 means of this reaction they found that Tantar's product contains 

 no percarbonate, so that its formula should be given as Na 2 C0 3 + 

 l^Rfi^.—Berichte, xlii, 4377. h. l. w. 



3. A Practical Application of Radium. — In connection with 

 a research on a revision of the atomic weights of iodine and 

 silver, Baxter and Tilley found it necessary to determine 

 small quantities of water in the iodine pentoxide which they 

 were analyzing. This water was absorbed and weighed in glass 

 U-tubes containing phosphorus pentoxide. The usual difficulty 

 in weighing glass apparatus, due to electrical disturbance from 

 wiping it, w r as avoided here by placing in the balance a few 

 milligrams of radium bromide of radio-activity 10*000 to dispel 

 electrical charges. Under these conditions no difficulty was 

 experienced in weighing the tubes within a few hundredths of a 

 milligram, since they quickly came to constancy in the balance 

 case and retained their weights unchanged for days at a time. — 

 Jour. Amer. Chem. Soc, xxxi, 212. h. l. w. 



