1415 
is formed; the liquid contains then 22 °/, As,O, and 2.87 °/, NH,. On 
further addition of NH, the solution keeps the composition 6 as long 
as the complex remains within the threephasetriangle 6. Da, . As,0,, 
and we have the complex: As,O, + NH,AsO, + solution 6. The 
only thing that happens on addition of NH, is the conversion of 
As,O, into NH,AsO,. When all the As,O, has disappeared and has 
been converted into NH,AsO,, then on further addition of NH, the 
solution follows curve bed, in which ease its content of As,O, 
decreases continuously. 
Leiden, Anorg. Chem. Lab. 
Chemistry. — “The allotropy of potassium.” I. By Prof. Ernst 
Conen and Dr. 5. Worrr. 
1. We have in view to investigate here whether potassium as 
it has been known hitherto is a metastable system in consequence 
of the simultaneous presence of two or more allotropic forms of 
this metal. 
It will become evident from the following lines that the literature 
already contains very accurate data for solving this problem. 
2. As long as thirty years ago Ernst HAGEN') published his 
very careful experiments on the determination of the coefficient of 
expansion of potassium, which were carried out with the dilatometer. 
Contrarily to many other physicists he bestowed much care on 
the purity of the material used. The specimen of potassium experi- 
mented with contained only a trace of sodium (in 6 or 7 grams). 
3. For a description of the details of the measurements the 
reader is referred to the original paper, but it may be pointed out 
here that the agreement between the determinations made with two 
different dilatometers (containing + 40 grams of potassium each) 
was exceedingly satisfactory. 
The measurements are summarized in the Tables I and II, where 
¢ indicates the temperatures at which the experiments were made, 
while v indicates the volume (in ccm.) of 1 gram of the metal. 
1) Wied, Ann. 19, 436 (1883), 
