Well, apart from a couple of comments suggesting a possible lack of particles 
in solution {which is not applicable I might add} it would appear nobody has an 
explanation, or has ever experienced my little quandary with lasers?

 

Praps one of the more 'knowledgable' folk among us who are into experimentation 
and/or research {gurus <g>} may wish to pick the ball up and run with it by 
getting hold of a red laser of <1mW and run the batteries down and see if they 
get a similar occurrance, although, if my issue happens with an El Cheapo 
freebie laser I can't see why it wouldn't do the same thing with my more 
expensive ones, lasers are lasers.  They either operate, or they don't...DO 
THEY?

 

It's fine to assume that battery power falling below *some?* threshold may 
affect the operational function of a laser, nevertheless it doesn't afford a 
suitable explanation as to what one would expect to observe in such an 
eventuallity when making observations of colloids in liquids?

 

At this stage I've gotta be thinking the use of lasers for determining pretty 
much *anything* with solutions is questionable...[battery reserve dependant!]  
That could be a trap for young players I suspect.

 

Guess I'll just have to wait til some batteries have drained in one of my other 
more expensive lasers and do some more observations to find out.  BUT, it still 
won't give me an explanation as to WHY the light fails to backscatter off 
particles as it passes through that liquid?

 

How about this then...

 

What if I were to suggest that if battery power falls below a specific 
operational threshold it may alter the wavelength and if particles are smaller 
than that wavelength then the light may pass *straight through* the liquid but 
the particles FAIL to backscatter that light?

 

N.
                                          
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