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From your description, it seems to be a well designed flow system.  But, the motion seemed to be oscillatory, which made me think it had a hydraulic cause.  If Schlieren effects, an eddy in the chamber may be causing the higher RI solution to move back and forth as it mixes.  Switching between similar solutions, as proposed by Stan, (including 2 propionates)  would be a good test for motion.  


Glen MacDonald
	Core for Communication Research
Virginia Merrill Bloedel Hearing Research Center
	Cellular Morphology Core
Center on Human Development and Disability
Box 357923
University of Washington
Seattle, WA 98195-7923  USA
(206) 616-4156
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On Mar 21, 2013, at 3:40 AM, Christof Schwiening <[log in to unmask]> wrote:

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> 
> Dear Glen,
> The solutions are gravity-fed via independent tubes from the base of 50 ml 
> syringes suspended about 50cm above the microscope stage. The tubes are 
> identical and are connected to electrical on-off valves (General Valves). The 
> tubes meet at a manifold about 15 cm from the output. In the case of the 
> video the output is directly onto the top of a fixed-preparation (Convallaria) 
> slide which was mounted directly onto the fixed platform of the microscope. 
> The output tube was about 2 mm from the objective at the level of the slide. 
> The suction was similarly sighted about 2 mm from the objective at an angle of 
> 180 degrees to the input. The suction was from a bottle (2 L) maintained a 
> low pressure with a high frequency low volume pump. The only oscillations that 
> occur within the system are surface tension effects on the suction when air 
> mixes with the water in the output lines - this occurs all of the time and 
> sounds like a child sucking through a straw from an empty glass of lemonade!
> I doubt that it is movement. I guess I would need a force transducer mounted 
> on the slide to prove that.
> Greetings,
> Christof