811 
or black stripes and without veil, while the contrast between the 
different blackenings appear as strong as possible. Glycin proves to 
come up to the requirements, if the proper conditions are chosen 
viz.: of the concentration of the developer, of the duration and the 
temperature of development. In fulfilling all these conditions a fine 
equal spectrum can be obtained with glycine, which — with respect 
to abundance of contrasts — is even preferable to the one produced 
by hydroquinone. 
5. The method nsed will be illustrated further with the measuring 
of the extinction of para-azoxyanisol. This substance was chosen in 
connection with the above mentioned research of Dr. W.J. H. Moun 
and Prof. Dr. L. S. Ornstein. For the phases: isotropic-liquid, 
ex-solid and ex-liquid the spectrum of absorption is determined. As 
these phases cannot exist at the temperature of the room the substance 
had to be heated and to be kept ata constant temperature. For this purpose 
we made use of a small electrical oven, consisting of a hollow 
brass cylinder, wrapped up with manganine-wire, through which a 
current was sent. By regulating this current each desired temperature 
may be obtained in the oven. A woollen mantle protected the wind- 
ings from changes in the temperature of the surroundings. In the 
middle of the cylinder the wrapping is interrupted over a length of 
1e.m., and there, diametrically opposite to each other, two perpen- 
dicular openings are bored, where a strip of copper K is fitted, 
carrying the glass cuvet with the substance. The small cuvet inclosing 
the preparation is constructed according to the principle of the 
numbering-chambers of Zriss: along the borders of a flat glass plate 
A, long narrow little beams of glass are stuck (height = 1,53 m.m) 
by means of water-glass mixed with asbestos. Great care is taken to 
make this glass-enclosure equally high throughout. For cover-glass 
we used a glass plate B of the same dimensions as A, carrying at 
the centre of the lower-side a small round piece of glass C (height 
= 0.90 m.m.). By pressing the borders of B close to the little beams 
_ on A, the distance between A and C, at the point where the sub- 
stance is to be examined, amounts to 0.63 m.m. 
On account of the high temperature necessary to melt the para- 
azoxyanisol it was quite difficult to find a glue which remains 
absolutely transparent under these conditions. The water-glass too, 
which was originally used to stick B to C, got opaque after some 
time. A solution of this difficulty was found by making a hole in 
the centre of the cover-glass B, so that C had to be fastened only 
at its borders. Between the two glass plates A and B in the middle 
