988 
PROFESSOR J. FT. LOCKYER ON THE PHOTOGRAPHIC 
For the region between K and F ordinary Mawson and. Swan “Castle” plates 
were used. But for the parts of the spectrum less refrangible than F specially 
prepared plates had to be employed. Plates dyed with the following solution were 
found to give the best results between F and D :— 
Erythrosin (1 :1000) . . . . = 1 oz. 
Alcohol.= 1 „ 
Distilled water.= 8 „ 
Ammonia (10 per cent, solution) =1 ,, 
“ Castle ” plates were immersed in this bath for two minutes, and were afterwards 
drained on blotting paper, film outwards, and stood on end to dry. They are then 
ready for use, and require about the same exposure as is necessary for the blue end of 
the spectrum with undyed plates. 
For the region D to A the plates require different treatment. Two baths are made 
up as follows :— 
No. 1. 
No. 2, 
Alcohol. 
6 oz. 
Cyanin (1 : 1000) 
100 minims. 
Ammonia .... 
. 10 „ 
Alizarin blue (1 : 1000) 
10 „ 
Distilled water . 
1 
• 2 55 
Alcohol. 
6 oz. 
Ammonia. 
1 
2 5 ) 
Distilled water . 
10 „ 
The plate is first placed in No. 1 for a minute, lifted out, drained and placed in 
No. 2 for the same time; it is then drained and put back in No. 1 for a minute, after 
which it is dried as before. 
Plates treated in this manner give the best results if used the day after prepara¬ 
tion ; they should never be kept more than three days. The exposure necessary for 
the red end with these plates is about twelve times that required by ordinary plates 
for the more refrangible regions of the spectrum. 
The ordinary 2 :>lates and those stained with erythrosin needed no S 2 )ecial develojDers. 
But in the case of those dyed with cyanin a weak developer is necessary. The one 
used for the develoi^ment of a ciuarter-jjlate is made uj) as follows :— 
Pyrogallic acid ... 2 grains. 
Ammonium bromide . ^ grain to 1 oz. of water. 
Ammonia.2 minims to 1 oz. of water. 
The ^date is flooded with this mixture and gently rocked for a few minutes, another 
minim or two of ammonia is then added, and development continued in the usual 
manner. 
Since the plates dyed with cyanin are sensitive to the red end of the sjDectrum as 
well as the blue, they must be jDrepared and develojjed in absolute darkness, and it is 
