Albert's collodion emulsion contains the same modification of silver bromide as the ordinary well known collodion emulsion - that is to say, a white silver bromide, sensitive to the violet and indigo rays of the spectrum.
Experiments have shown that there is no difference between Albert's emulsion in the undyed state and the collodion emulsion as hitherto well known. The novelty lies only in the colour-sen-sitiser. With regard to the latter, it has been already stated that it contains erythrosin, but that silver could not be recognised therein by the accuse tomed test of hydrochloric acid. Close examination of the matter shows that eosin silver dissolved in dilute nitric acid only gives a precipitate with hydro* chloric acid when there is a little silver nitrate in excess: otherwise not.
Further trials with Albert's portrait dye solution gave results unmistakably like those obtained with a solution of eosin silver in ammonia. Both solutions showed, when carefully neutralised with nitric acid, a cloudiness, and precipitation of red erythrosin silver. Albert's colour solution, however, proved to be in a more concentrated state than a saturated solution (about 1 to 1000) of erythrosin in alcohol.
From various trials it was found that erythrosin is much more soluble in methyl alcohol than in ethyl alcohol, and that a solution of 1 part of erythrosin in 200 parts of methyl alcohol was more intense in colour than Albert's solution. This solution (of erythrosin in methyl alcohol) was then added in the proportion of 1 in 10 to the collodion emulsion, and tried. The colour-sensitiveness proved, however, to be but slight, and did not approach that of Albert's preparation.
The dye solution was now mixed with an alcoholic solution of silver, and the precipitate was redissolved in alcoholic ammonia. The solution thus obtained was added to 10 times its amount of bromo-silver collodion emulsion. Thus was obtained an emulsion which corresponded completely with Albert's portrait dye collodion, both, in colour-sensitiveness and in general sensitiveness. Addition of picric acid made not the slightest difference to it.
There remains no doubt that Albert's colour-sensitive collodion emulsion (for portraits) consists for the one part of a collodion emulsion prepared in the customary way and for the other part of a very concentrated solution of ery-throein silver in methyl alcohol and ammonia, with some picric acid. The value of the picric acid remains undecided. To Dr. Albert, however, is due the credit of having first discovered the surprising sensitising power of a very concentrated solution of eosin silver in ammonia. Without his example others Would not so quickly have come upon the interesting fact that it is possible to prepare colour-sensitive collodion emulsion attaining the sensitiveness of gelatine emulsion. Dr. Albert has thereby opened a new road.
Formula for an erythrosin silver dye solution:
A. - Erythrosin .. .. 0.5 grm, Pure methyl alcohol 100 cc.
B. - Silver nitrate .. 4grm. Warm water .. 4 cc.
After solution, add 96 cc. pure alcohol at 96°. 10 cc. of A is mixed with 1 cc. of B and 4 cc. of alcohol (not aqueous) ammonia. This mixture will keep.
For use, 1 part of the solution is shaken up with 10 of bromide-silver collodion emulsion.
1. - Hydroquinone . 10 grm.
Soda sulphite.. ... 50 grm.
Water .. .. 700 cc. 2. - Crystallised soda carbonate . 100 grm.
Water .. .. .. 800 cc.
. 60 cc.No. 1 are mixed with 10 cc. of No. 2, and 2 or 3 drops of a 10 per cent. solution of ammonia bromide are added thereto.