a speed depending on the concentrations between the mixtures (as well as depending
on the system dimensions, diffusion coefficients ratio and form of the boundaries, but
these parameters were the same in all our experiments).
The CCD camera records the image and sends it to the computer. This gives us
an opportunity to store the received image and process it later. In this way, the main
characteristics of the “salt finger” cells such as planar form, area, width as well as the
rate of growth were obtained.
In our experiments, the beaker was filled with dyed sugar solution. We usually
prepared 200 ml of the sugar solution with various concentrations (from 6 to 19 g=l)
and added approximately 8 drops of blue ink (a fluorescent compound can be used as
well). The next step was to insert salt solution (200 ml, concentration 10 g=l) below
the sugar solution. For the purpose of restricting the fast mixing of the salt and sugar
solutions, we poured the salt solution very slowly through the glass tube, which was
placed close to the bottom of the beaker. The clip was used in order to regulate the
speed at which the salt solution was poured.
4. Results of measurements
The results of our measurements are represented in this section. The experimental
data include the shadowgraph images (see Figs. 2 and 3) of the obtained cells and their
side view. We investigated the main characteristics of the “salt fingers”: area, type of
planar form (the number of vertexes) and the rate of growth at the various salt and
sugar concentrations as well as at different volumes of the double-diffusive layers.