385 
afterwards to the value found for the force, which drives the sinker 
upwards. Also in the case of the molten salts ANO,, NaNQ,, 
LiNO,, ete. the absolute values for dao appeared to agree with 
those of Goopwin and Mamer 5, if only the observed hydrostatic 
force was augmented with 0.000L x; the temperature-coefficient of 
d4o moreover appeared to be independent of this correction too. 
However, the dates obtained in this way, and especially those at 
extreme temperatures, can only be considered quite exact in two 
decimals, and the accuracy never surpasses three: or four units of 
the third decimal. For the proposed purpose this degree of accuracy 
is sufficient; but, moreover, it may be asked if it is possible at all 
to obtain more accurate data at such extreme temperatures in 
some other way? Circumstances are rather unfavourable in these 
measurements; for an increase of the upwards driving force by the 
choice of a sinker of greater volume, as Goopwin and Mairrr did 
(loco cit), can hardly be considered a real improvement, because the 
condition of an everywhere equal and homogeneously distributed tem- 
perature can only be fulfilled by a volume (as small as possible) of 
the molten mass and of the whole apparatus in the furnace. Only 
then the furnace can be used as a real thermostat at very high 
temperatures *). Platinum is moreover at such high temperatures the 
only fit material to use; but because of its very high specific 
weight, the volume of an even very heavy sinker will be only 
relatively small, and consequently also the observed upwards driving 
force. There are a number of other disturbing circumstances, e.g. 
the rather strong damping of the swinging balance, ifeliquids of 
appreciable viscosity or surface-tension are investigated; in such cases 
it is absolutely necessary to keep the liquid at the same temperature 
for a longer time, if one wishes to be certain of established equili- 
brium, which must moreover be checked in several ways. All such 
circumstances diminish the degree of accuracy more or less, so 
that one may finally be glad to reach the degree of. agreement 
of repeated determinations here mentioned. Especially will this be 
the case, as most of these molten salts appear to decompose gradu- 
ally more or less at very high temperatures by, or without, the 
water-vapour of the atmosphere; their chemical composition being 
thus altered at the same rate. | 
Another difficulty again presented itself in measurements of this 
kind, which is caused by the fact, that most substances possess 
2) F. M. Jagecer, Eine Anleitung zur Ausführung exakter physiko-chemischer 
Messungen, u. s. w. Seile: 57, 59, u s. w. 
25 
Proceedings Royal Acad. Ainsterdam Vol. XIX. 
