LIPPMANN HELIOCHROMES—CAJAL. 257 
According to the author’s views complete fixation of the pictures, 
even when all other operations, such as exposure, development, inten- 
sification, etc., have proceeded normally, causes with normal, or 
almost normal, illumination at least, a slight shift in the direction 
of the more refrangible end of the spectrum, a fault which can not 
be remedied, as mounting under a prism would only slightly increase 
the shift; and if this failure has been less frequently observed than 
the opposite one (that is, too great a distance between the lamine), it 
is due to vigorous intensification, which compensates, to a certain 
extent, the contraction of the intervals between the lamine, actually 
by thickening the first one. 
It is obvious from the researches that the most frequent unperfec- 
tions of Lippmann heliochromes is due to the almost unavoidable 
changes of the normal distance between the lamin, a change caused 
by the mechanism of the photographic operations. Under certain 
conditions—complete fixation, too short exposure, too short develop- 
ment, etc.—the lamin are too near one another, and the colors shift 
toward the blue. In other and much less frequently occurring 
failures the lamine become thicker, the reflecting surfaces are farther 
separated from one another, and the colors are then shifted toward 
the red. 
ANALYSIS OF PICTURES WITH MATT FAINT COLORS. 
Many emulsions, in spite of great transparency, show a tendency 
to give only matt colors, and actually do not give white. A micro- 
scopical examination of such plates proves that the cause of this 
phenomenon is due to too little contrast between the laminz and the 
intervals. The former are formed in sufficient number, but from their 
yellowish or bright greenish-gray color are not sufficiently differen- 
tiated from the more or less gray intervals. The mirror zone which 
reproduces the white is very pale and transparent, and possesses no 
reflective power. f 
In order to obviate this very frequent fault, which unfortunately 
occurs with every third or fourth emulsion, the author has made 
many experiments and obtained successful results by alteration of 
the developer. To increase the contrasts between the lamine and the 
intervals the following should be used: 
ccs. 
POtaSSOLomid eye OR per rCeni ts SO] sas ee a ee ee 20 
SATIATION Ee women hee en Re Ls el ee Be ee 1-1.5 
Byron Der iCents SO] eens oe y= ae ee ee tS 
AMVACOTY ce reaee Ree Parte Ae gt: eee Vea Pee ee 2 ee!) ae 250 
and the general rule is: Reduction phenomena appear very quickly 
in the intervals with an excess of ammonia, while the opacity of the 
lamin is increased by an excess of bromide and pyro; but the laminz 
ought not to be so opaque as to prevent the intensifying action of 
the deeper lying ones. 
