398 MAEION I. NEWBiaiN. 



On the addition of a considerable amount of hydrochloric acid 

 its limits are as follows : 



X 669 - X 637, c. = X 653 (see the first band of fig. 2). 



It will thus be seen that in spite of the fact that the solution has 

 been very considerably diluted, the actual extent of the band 

 has not been greatly diminished. Further, while the left-hand 

 side of the band remains fairly sharp and well defined, the 

 right-hand side is very indefinite, shading gradually off, so that 

 exact measurement is virtually impossible. This peculiar 

 appearance has been described by Dr. MacMunn (6) in the 

 case of solutions of enterochlorophyll as " a band super- 

 imposed upon a shading." Now if excess of acid be added to 

 this solution until it turns green, this shading at the right 

 hand disappears, and the band recovers approximately its 

 original position. Thus it may stand as follows : 



X 677 - X 647, c. = X 662. 



As to the other bands of this green acid solution, they may be 

 present as in the blue acid one, but in the general case they are 

 exceedingly faint, and present merely as traces. Their changes, 

 if they do change, can be followed with much less certainty 

 than those which are undergone by the very distinct band in 

 the red. These changes are not sudden, but take place very 

 gradually, and can be watched step by step when acid is added 

 to a solution suspended in front of the slit of the spectroscope. 

 As the acid is added the band moves to the right until the 

 movement reaches its maximum, and then on further addition 

 of acid it moves back to its original position. Further, if 

 alkali be added to a very strongly acid solution the band shows 

 the same change of position as when little acid is added to a 

 normal solution, and excess of alkali restores it to its original 

 position, just as does excess of acid in the other case. In other 

 words, dilute acid produces a change in the position of the band, 

 which is reversed by strong acid ; and it is unimportant whether 

 the dilute acid is directly added to the solution, or produced by 

 removing some of the acid from a highly acidified solution. In 

 the case of bonellin, Krukenberg states that the strongly 



