MadSci Network: Chemistry

Re: How would you test for potassium cyanide?

Date: Mon Oct 23 10:05:49 2000
Posted By: Dave Clark, Staff, Chemical and Environmental Technologies, Battelle
Area of science: Chemistry
ID: 971876711.Ch

Unfortunately, testing for cyanide is not that easy.  The usual way it is 
done is to react the unknown material (peach pits) with chlorine.  Any 
cyanide present reacts with the chlorine to form cyanogen chloride.  This 
then reacts with pyridine to form a dialdehyde (glutocondialdehyde).  That 
is reacted with a special acid (1,3-dimethylbarbituric acid)to form a deep 
purple color (violet polymethine dye).  The intensity of the color is 
related to how much cyanide was present to begin with.

The GOOD NEWS is that there are simple test kits available that do all the 
chemistry for you.  All you have to do is mash up the peach pits and let 
them soak in distilled water - stir occasionally.  Then dip in a special 
paper strip or add a drop of a special solution and let the color change.  
You can then compare the color on the strip to reference colors on a card 
that comes with the kit. Unfortunately, the strips are fairly expensive. 

Strips are available from EM Science Products (; 1-800-
222-0342)  Cyanide Test Strips, 1-30 parts per million, EM Quant
Part No  10044-1, 100 test strips, $64.45

Sometimes companies are willing to donate small amounts of supplies to 
schools for free.  You or your teacher could give them a call and see if 
they'd be willing to send you a kit for free.

Good luck!

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