392 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On Low Temperature Experiments. — In consequence of the 

 easy production of liquid oxygen and nitrogen in recent times, 

 experiments at low temperatures have hecome common. Hempel 

 has called attention to the fact, however, that with much simpler 

 means than these, temperatures sufficing for the greater part of 

 the ordinary reactions can be secured. Thus, for example, liquid 

 carbon dioxide, now commercially very cheap, may readily be 

 employed to show that potassium and bromine no longer react on 

 each other at low temperatures. If the bromine be first placed 

 in a mixture of solid carbon dioxide and ether and thoroughly 

 cooled, and then a piece of potassium, cooled in a similar bath, 

 be introduced into it in a small spoon, no combination takes 

 place ; though it speedily sets in as the temperature of the mix- 

 ture rises. Very considerable improvements, however, are neces- 

 sary in the methods of manipulation. The double-walled and 

 exhausted globe of Dewar, therefore, has been of great service. 

 But these Dewar globes are costly and fragile when they are of 

 large size ; and hence are not available for laboratory experi- 

 ments on any large scale. The author therefore has experimented 

 to determine to what extent a sufficient isolation can be secured 

 in other ways. Test tubes 4 cm in diameter, approximately of the 

 same size as the Dewar tubes, were placed in beakers 13 cm in 

 diameter, the space between being packed with the material to be 

 tested. Equal quantities of solid carbon dioxide and ether were 

 placed in each of these tubes; so that at the beginning of the 

 experiment all the vessels contained equal quantities of material 

 at —79°. From time to time the temperature in the several tubes 

 was determined by an electric pyrometer. In 5 minutes the 

 tube packed with cotton had a temperature of —76°, that with 

 wool —77°, that with eider-down —78°, and that with a well 

 exhausted Dewar tube —77°. Alter 58 minutes these values 

 were successively —56°, —64°, —67°, and —54° ; thus showing 

 that well dried wool and eider-down are very good insulators, 

 being exceeded only by the best Dewar tubes. For preparing 

 the solid carbon dioxide the author prefers a paper funnel with a 

 wide short neck, to the upper edge of which is fastened a cylin- 

 drical bag of linen. On clasping the upper portion of this bag 

 about the valve on the cylinder containing the liquid gas, and 

 opening this valve, the solidified gas collects in the bag and may 

 be readily shaken into the funnel. About 270-300 gms. of the 

 solid are obtained from a kilogram of liquid ; and since this liquid 

 costs about 15 cents a kilogram, the solid would cost not far 

 from fifty cents a kilogram. No advantage in yield was found to 

 result on cooling the liquid before expansion. The lowest tem- 

 perature is obtained when the solid carbon dioxide is mixed with 



