By means of snch a cleavage-lamella, 1,65 mm. thick, we obtained 
a Röntgen-image, completely analogous to that of the corresponding 
selenate, and which only manifested another distribution of the 
intensities of the diffraction-spots; this last phenomenon will be 
discussed in the following paper more in detail. 
The obtained photo is reproduced in fig. 5 on Plate II, and 
in stereographical projection in fig. 10 on Plate IV. The Röntgen- 
pattern possesses a quaternary principal axis, and four planes of 
symmetry intersecting at angles of 45°, — just as was theoretically 
expected. 
c. Finally we investigated also a plate of Strychnine-sulphate : 
(C,, H,, N, V,),.H,SO,+6 H,O, cut perpendicular to the optical 
axis. This laevogyratory substance, whose parameters are: @:¢ = 
1: 3,312, belongs to this symmetry-class too. 
Indeed the pattern obtained with such a plate parallel to {O01}, 
and 1,76 mm. thick, showed the aspect of the projection-figure 18 
on Plate IV. Here also the quaternary axis and the four planes of 
symmetry passing through it, are immediately discernible. In con- 
nection with the relatively great ratio «:c, the principal spots appear 
crowded in a smaller distance from the central part of the figure. 
On a former occasion we have mentioned already the very 
strongly dextro-, resp. laevogyratory Priethylenediamine-cobalti-bro- 
mide (+ 2H,0), which also erystallises in the tetragonal system, 
and which belongs either in this class, or in the bipyramidal one. 
In every case it can be seen from the approximative stereographical 
projection of the Röntgenpattern parallel (O01), which is reproduced 
once more in fig. 19 on Plate TV, that notwithstanding the strong 
rotatory power of the crystals, clearly four planes of symmetry can 
be discerned passing through the principal axis. 
WV. Tetragonat-scalenohedrical Class. 
a. The only substance belonging to this class, which could be 
obtained in crystals suitable for our purpose, was Potassium-dihydro- 
ortho-phosphate: KH,PO,, with the axial ratio: a:¢c=1:0,9391. 
The Röntgenpatterns, which were obtained with erystal-plates parallel 
to (001), (100) and (110), «/= resp. 1,20, 1,13 and 1,25 mm, 
were so feeble, that with the exception of the image parallel to (110) 
(see fig. 9 on Plate III), they were unsuitable for direct reproduc- 
tion. Therefore the corresponding stereographical projections are 
given in fig. 13, L4 and 15 on Plate IV. They prove, that the 
image parallel to (OOI) possesses a quaternary axis and four vertical 
planes of symmetry passing through it, while both the other patterns 
sbow a binary axis and two planes of symmetry perpendicular to 
