Few years later, Stern [8] publishedanother article devotedto the same problem. He
suggested that interaction between the “salt ngers” actually results in hydrodynamic
instability.
3. Experimental observations ofthe “salt ngers”
The double-di$usive phenomenon has been thoughtfully investigated in numerous
experiments beginning with very simple ones, in which “salt ngers” were explored
in a qualitative way, andend ing with very sophisticatedexperiments, in which “salt
ngers” were examinedquantitatively.
Various Gow visualization methods are applied in the investigation of the doubledi
$usive systems: shadowgraph photography, streak photography may be exploited to
make exploratory studies of the motions which can arise as a consequence of opposing
vertical gradients [2–4]. Besides that, the elegant optical methods, which provide a
means for the “salt nger” morphology exploration on the basis of density as well as
refraction index distribution in the double-di$usive system, were employed by Shirtcli$e
[5,9 –11].
Today, it is possible to use chargedcoupledd evices (CCD camera) to track, record
and investigate the double-di$usive systems, as was done in our experiments. We
carried out a quantitative experiment by means of optical tools in order to determine
the typical characteristics of the “salt ngers” such as the planar form, width, length,
area andrate of growth.
In this section, a short outline of the experimental setup is given (see Fig. 1).
We took a glass beaker of volume 800 ml (1), a funnel (2), a glass tube (3) and