853 
1. Plates developed with hydroquinone *). 
The plates N°. 1—4 have been developed for 7 '/, minutes with 
1 part of developer and 6 parts of water, plate 1 at 14.5°, plate 
2—4 at 13°, the plates 5—10 have been developed at 13° for four 
minutes with 1 part of developer and 3 parts of water. After 
development all the plates were rinsed for '/, minute, fixed for 
15 minutes, and rinsed for 2 hours. 
In the plates 5—10 the two most uniformly blackened pieces of 
15 cm? were chosen on each plate. These two pieces are denoted 
by A and B in the adjoined tables. Of each piece of 15 cm?’ the 
blackening is measured at three different spots. The area of the 
beam of rays on the photographic plate amounting to about 4 cm’, 
the blackening is directly determined on 12 em’ of the 15 cm’. 
The blackening given is a mean of these three. 
In the plates 2—4 two pieces of 65 cm’ are taken, because on 
account of the slight blackening a larger area must be used in the 
determination of silver to be described later. The blackening is 
measured in four places in every piece. The blackening given is 
the mean of these four. 
In plate 1 the different blackenings — marked a, 8, y, and 0 in 
the table — are so slight, that no determinations of silver can be 
made with them. 
Accordingly the blackening is measured only at one place, but 
always twice. 
2 Plates developed with glycin ’). 
The plates N°. 11—19 have been developed at 18° for 7'/, minutes 
with 1 part of glycin and 2 parts of water, and they have further 
been treated in the same way as the plates 5—10 with hydroquinone. 
As with glycin a cloud occurs near the blackened part, a very broad 
region of the plate is left unilluminated in the plates developed 
with glycin, and the resistance A, of the unblackened plate is 
measured at a place sufficiently far from the clouded part of the plate. 
The blackening is measured for all plates for the following colours. 
a. For the whole spectrum except for ultra-red. 
~The dish Ct in the light path of the lamp Zp is filled with a 
3°/, copper-chloride solution; filter /’r is superfluous here. 
6. For ultra-red; centre of the intensity estimated at 1,25 u. The 
) We take Wellington plates, Speed -100, developed with Hydroquinone 
and bromide of potassium to get plates with small grains. 
*) We wish to make the blackening and the filter investigation for two 
different developers. As second developer we take glycin without potassium 
of bromide, because we then get a fairly constant and not too large grain. 
