dip | 
formed by the involutions (2,, Zit, 2,) belonging to the conics of 
the pencil (8%). 
The curves 6° belonging to two base-points B, B, ($ 6) have in 
those points 12 intersections and 8 in 46,, 4,; they further pass 
through the eyelie points on /, and through the point at infinity 
" 
of B,B,. The two points S, which they lave moreover in common 
are each the end of two chords of osculation BS, b,S. Any two 
base-points belong therefore to two groups of 7;. 
Let us now consider the locus of the points 2,, R, belonging to 
R, =8,. This singular curve, @,, has nodes in B,, B,,.6,, but does 
not pass through B,, 7, possessing no coincidences outside /,. As 
an arbitrary conic of (8°) contains one pair R,, &,, consequently has 
eight points in common with 8,, each base-point determines a rational 
singular curve of order four. 
The parabolae too are singular curves and as such associated to 
their points at infinity. 
Any straight line Bj B, corresponds to itself in the transformation 
(R,, R,); for each of its points may be considered as point of 
contact of a y,, intersecting 6, 6, on /. 
If AR, describes a A’, B? is described twice by &, (A). So Bp’ is 
transformed by (/?,, R,) into the figure composed of the four singular 
curves 8. and the conic 8? counted twice, consequently into a 
figure of order 20. From this it ensues that the transformation im 
question transforms a straight line into a curve of order ten. 
This c'° has in each base-point a quadruple point. 
Prof. 
— 
Cit 
Chemistry. — “Compounds of the arsenious owide”. 1. H 
F. A. H. SCHREINEMAKERS and Miss W. C. pi Baar. 
The system: H,O—As,0,—NH, at 30°. 
Of the different ammonium arsenites which may be imagined to 
be deduced of the H,AsO,, H,As,O, and. HAsO,, (NH,),As,O, and 
NH,AsO, are described as crystals and (NH,),AsO, as a thick-fluid 
yellow mass. 
Now we have examined the system H,O—As,O,—NH, at 30°; 
from this it is apparent that the salt NH,AsO, oceurs at 30°, while 
the possibility that also still a sait of the composition NH,H,AsO, 
exists, is not excluded. 
In fig. 1 we find a schematical representation of the equilibria 
occurring in this system at 30°; with the aid of table L we can 
accurately draw the different curves. 
