470 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistey and Physics. 



1. On Thermal Phenomena attending Change in Rotatory 

 Power.— -It is well known that certain carbohydrates, at the 

 moment of solution in water, show an abnormal circular polari- 

 zation ; and that optical stability in such solutions, at ordinary 

 temperatures, is attained only very slowly. This phenomenon, 

 which was first observed in dextrose and milk sugar, was called 

 birotation, since it was believed that the circular polarization of 

 the freshly prepared solution was twice that of the rotation 

 finally reached. Subsequent investigations, however, have shown 

 that even in these cases the ratio of the rotations is never exactly 

 2:1, and further, that dextrose and milk sugar are capable of exist- 

 ing transitorily in solution in more than two optical conditions; and 

 this, coupled with the fact that the rotatory power of a freshly 

 made solution of maltose is actually less than its subsequent value, 

 has caused the term multi-rotation to be adopted as preferable. 

 Now it has been observed that when a substance capable of show- 

 ing this property is originally produced by the hydrolysis of 

 another carbohydrate of greater molecular complexity, the 

 phenomenon of multi-rotation also appears. And Brown and 

 Pickering have sought to ascertain whether this change in 

 optical properties is attended by any corresponding heat change. 

 Three optically different forms of dextrose have been described 

 by Tanret. His a-dextrose is the so-called birotatory substance, 

 /3-dextrose being the ordinary optically stable form. His y-dex- 

 trose, produced by heating amorphous dextrose to 100°-110°, has 

 an abnormally low rotation when freshly dissolved. Since dex- 

 trose is produced by hydrolysis in the a form, the authors deter- 

 mined the heat change when this form was converted into ft by 

 adding 0*01 per cent of soda solution, the operation being con- 

 ducted in a suitable calorimeter, and a check determination 

 being made by using the dextrose in a second experiment, already 

 in the ft form. The corrected mean of four values is given as 

 0*588 calory per gram of substance. Plotting the heat changes 

 thus obtained after various intervals of time and comparing the 

 curve with that given by Parous and Tollens for the late of 

 change of rotatory power, it appears that, while the heat curve is 

 somewhat flatter, the general character of the two curves is the 

 same. Thus making it probable that "the special physical or 

 chemical changes which determine the gradual alteration or 

 specific rotation in freshly prepared dextrose solutions proceed 

 pari passu with the heat evolution," and therefore "that this 

 evolution is the result of the changes in question." Similar 

 experiments were made with maltose, with levulose and with 

 milk sugar. No change of temperature was detected with the 

 first, while levulose gave —4*64 calories per gram and milk sugar 



