678 
to pressures of 500 ky. per cem°. There was therefore every reason 
to rejoice that Mr. Deens, when revising his Thesis for the Docto- 
rate: “Legeeringen van tin en lood” (Alloys of tin and lead) wanted 
to make another attempt to tind the expected transition between 
tetragonal and rhombic tin in a dilatometrie way, though his prede- 
cessors had only obtained negative results. 
As Mr. Dreers found it impossible to obtain reliable results 
with paraffin oil, which had been used as dilatometric liquid by 
ConeN and GOLDSCHMIDT, in consequence of the generation of gas, 
however slight, one of us (Smits) advised Mr. Drcens to use an 
air-dilatometer with a twice bent capillary. To prevent any injuricus 
decomposition of the dilatometrie liquid, mercury was used by Mr. 
DeGeNs, to include the air in the dilatometer, although in this way 
there was, of course, a possibility that during the experiment, espe- 
cially when it had to be continued for a long time, appreciable 
quantities of gaseous mercury could be absorbed by the tin. Mr. 
Drcens, however, expressly states that “it was never observed (hat 
the metal was attacked by mercury vapours’. 
By the aid of this air-dilatometer Mr. Deraens really found an 
iidication about the existence of a point of transition, viz. at 161°. 
Since we have been occupied with the tin-problem, we have begun 
to mistrust this temperature, because different phenomena led us to 
expect a point of transition at + 200°. And as it seemed very 
desirable in connection with the already partially published investi- 
gation about the system tin, to know the exact situation of the 
point of transition between tetragonal and rhombic tin, an investi- 
gation was undertaken also by us to determine this point dilato- 
metrically. 
When we repeated Mr. Draers’ experiments we found first of 
all that by this way of procedure a point of transition can really 
be demonstrated, but that in successive experiments this point of 
transition descended. This pointed to an absorption of gaseous 
mercury by the tin during the experiment. On investigation of the 
tin used it appeared clearly that the tin contained appreciable quan- 
tities of mercury, which to our great regret condemned Mr. Drcens’ 
method. We regretted deeply that we had to come to this conclu- 
sion, particularly because Dr. Decens was known to one of us 
(Smits) as a man full of enthusiasm for his work, who carried out 
his investigations with great experimental skill, in the conviction of 
having left no means untried to test the validity of his results. In 
this case, however, he has been mistaken. 
In order to take the experiment in such-a way that the results 
