Invisible Ink

The CIA has declassified a number of documents from the first World War, some detailing the nature of invisible inks used at that time. These documents are available in the Freedom of Information Act Electronic Reading Room at cia.gov

One recipe for invisible ink was as follows
"A solution of nitrate of soda and starch in water may be carried for example in handkerchiefs or starched collars, starched shorts or anything else starched. These things being laid in this solution and then ironed. The article thus treated is later on again put in water and a solution obtained which can be used for invisible writing. The best means for developing are iodate of potassium."

And the recipe for developing the ink using potassium iodate
"Iodate of potassium, 5 grams with 100 grams of water, 2 g of tartaric acid added."

The beauty of this recipe for invisible ink is that the ingredients would be quite readily available to the spy.
Nitrate of soda (sodium nitrate) could be found in lawn fertilizers.
Iodate of potassium (potassium iodate) could be found in disinfectants.

As all science students know,
starch + iodine solution → blue-black iodine-starch complexBut a person carrying around a bottle of iodine solution may have been a bit suspicious during the war.
Potassium iodate can react with tartaric acid in aqueous solution to produce potassium iodide solution. The iodide ions released can react further with the iodate ions to produce aqueous iodine solution (I_2(aq)):
5I^-_(aq) + IO₃^-_(aq) + 6H⁺_(aq) → 3I_2(aq + 3H₂O_(l)


Reference
http://www.washingtonpost.com/world/cia-recipe-for-invisible-ink-among-newly-released-wwi-era-documents/2011/04/19/AFn5Ej7D_story.html
http://foia.cia.gov/CIAsOldest/Secret-writing-document-one.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-two.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-three.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-four.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-five.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-six.pdf

Further Reading
Naming Ionic Compounds
Writing Ionic Formula
Molecular Mass (Formula Weight)
Percentage Composition
Oxidation and Reduction
Oxidation States (numbers)

Study Questions:

1. Write the formula for each of the following
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
2. Calculate the molecular mass (formula weight) for each of the following:
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
3. Calculate the percentage composition of each of the following:
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
4. What is the oxidation state (oxidation number) of iodine in each of the following:
   
   • potassium iodide
     
   • potassium iodate
   • molecular iodine
5. In the reaction between iodide ions and iodate ions, which species are being
   • oxidized
   • reduced
6. Write half-reaction equations for each of the reactions below:
   
   • iodide → iodine
   • acidified iodate → iodine

Salivary Amylase

Wheat, potatoes, corn and rice contain starch and starch is a major component of the modern diet. Amylase enzymes secreted in saliva help break down starches into simple sugar molecules that can be absorbed into the bloodstream, influencing blood glucose levels.
Monell Center scientists have undertaken a study which revealed that changes of starch consistency in the mouth were directly related to salivary amylase activity. In this study:

• saliva was collected from 73 subjects
• saliva was mixed with a standardized starch solution, and a sensor measured the enzymatic break-down of the starch's consistency
• enzyme and protein assays directly measured the amount and activity of salivary amylase in the saliva samples
• subjects completed a survey to rate the perceived breakdown of a starch sample in the mouth over a minute

Foods with different starch levels were perceived differently by people depending on how much salivary amylase they produce. "What may seem like a thick and resistant pudding or starchy food to some may seem noticeably thin in the mouths of others", said Monell sensory geneticist Paul A. S. Breslin.
Individuals who have more salivary amylase may break down starchy foods more quickly, leading to more rapid increase of post-meal blood glucose levels. It is possible that high levels of salivary amylase contribute to the risk of insulin resistance and non-insulin dependent diabetes.

Reference:
Abigail L Mandel, Catherine Peyrot des Gachons, Kimberly L Plank, Suzanne Alarcon, Paul A S Breslin. Individual Differences in AMY1 Gene Copy Number, Salivary α-Amylase Levels, and the Perception of Oral Starch. PLoS ONE, 2010; DOI: 10.1371/journal.pone.0013352

Further Reading
http://www.ausetute.com.au/enzymes.html
http://www.ausetute.com.au/sugars.html

Study Questions

1. Give a general chemical formula for starch.
2. Starch is an example of a biological polymer. Of what monomers is this polymer made up of?
3. Another biological polymer is made up of the same monomers as that of starch, but, it is found in animals instead of plants. What is the name of this polymer?
4. Assuming you were given two sample bottles, one contained the plant polymer starch, and the other contained the animal polymer in question 3. What simple test or tests could you perform to identify which bottle contained the plant polymer and which contained the animal polymer?
5. What is meant by the term enzyme?
6. Draw a diagram to represent how amylase acts on starch to produce simple sugars.
7. Assume one of the subjects in the study had a fever and was found to have a temperature of 40^oC. What effect would this have on the results obtained during the survey phase of the study?
8. Imagine a well-wisher gave our sick subject above a "nice, hot lemon drink" to relieve the fever's symptons just before the saliva sample was collected. What impact would the lemon drink most likely have on the level of amylase activity?