1900] CHROMOGENIC BACTERIA 387 
obtained when 10™™ layers of such filtrates are examined, after 
having been diluted to a color intensity approximately equal to 
2 per liter of purified pigment. 
The addition of acids to the blue solutions causes an 
immediate displacement of the main band toward the violet, 
and increases its intensity at least twofold. The maximum 
intensity, of the main absorption band, of the now purple-red 
solutions is about A=570. The absorption in the red seems to be 
diminished, but that in the blue and violet slightly increased. 
In fig. 4, the effect of acetic acid is shown; in fig. 5 that of 
hydrochloric acid. In each case solutions of 2%" of the isolated 
pigment per liter, in layers 10™™ thick, were employed. /ig. 9 
shows the effect of acetic acid on the solutions used in jig. 76. 
Ammonium hydroxid added in excess to the pure blue solu- 
tion causes but little displacement of the main band, but greatly 
reduces its intensity, as also that of the bands in red and violet. 
This is not the result of dilution alone, however, since the addi- 
tion of a corresponding volume of water gives no similar reduc- 
tion in the intensities of the bands. Fig. 6 shows the action of 
this reagent in slight excess on solutions of 2" of the pig- 
ment per liter, when examined in layers 1o™™ in thickness. 
Fixed alkalies when added in very small amount first produce 
a violet color. Such solutions yield an absorption spectrum 
shown in fig. 7, in which sodium hydroxid has been added to a 
25" layer of a 2" per liter solution of pigment. Added in 
€xcess until a green results, the absorption band at D is almost 
completely destroyed, and the other bands about equally reduced 
in intensity, This effect is shown in fig. 70, where solid sodium 
hydroxid (to avoid dilution) has been added to solutions similar 
to those used for fig. 7. If the alkaline solution be shaken with 
air until it turns blue, a dark absorption band again appears, but 
hot in the same position as in the original solutions, for it has 
been displaced toward the red end of the spectrum , its maximum 
intensity now falls between A=605 and r=610. This change es 
Position is indicated in fig. 6, solutions similar to those used in 
fig. 16 being employed. 
