Just buy a used sofa off a guy with a van on craigslist? Find a knife stained red under the floorboards while insulating the attic? Enjoy CSI but hate how the show is super bad about science? Well, let’s play a game I’ll call: IS! THAT! BLOOD?
A little while back, 1853 to be specific, a fellow named Ludwik Karol Teichmann devised an amazingly simple and accurate test for blood. It’s called the Teichmann test or sometimes the hemin crystal test. It’s pretty simple to identify fresh blood from say, stage blood (corn syrup and red dye) or ketchup; blood has red cells and white cells, just make a smear and take a look under the microscope. Old blood, from as little a a few minutes to a few hours can be much harder to identify.
A great many things have cells and are red or brown when dry. Meaning simply re-hydrating a stain and checking for cells under a microscope is not enough to identify blood. If we were on television we could shine a blue light on it or poke it with a stick to test for DNA. Fortunately, human blood contains a number of compounds that are unique to it, and human DNA is just one. Hemoglobin is another and the Teichmann test, acts upon that hemoglobin to form easily identifiable hemin crystals and it works on even decades old samples. Most folks have everything they need right in their kitchen. If you don’t, a five dollar bill is enough to collect the needed supplies from the nearest grocery.
Acetic acid, anything from the purest laboratory grade glacial acetic acid to plain old white vinegar will work.
Sodium chloride, iodized salt will do but if there’s a choice it’s better to go with pure sodium chloride-pickling salt or Kosher salt for example.
Something that may or may not be blood.
A glass slip and cover.
A heat source-anything from a candle to a Bunsen burner will work.
Take the sodium chloride and pulverize it. Only a few grains of salt are needed and the smaller it can be crushed the easier things will go later. For this reason the flake style Kosher salt sold in the baking aisle can be. the best choice. Table salt grains can be effectively pulverized between two slips pressed together and rubbed gently over a third.
With a scalpel or razor knife take up a little of the material to be tested and scrape it onto the slip with the pulverized salt. Only a very little material needs to be used and the proportions of the salt to the possible blood are not important.
Using an eye-dropper introduce a few drops of acetic acid and place a coverslip over. Heat the slip gently just until bubbles are seen to form. It is not necessary or desirable to boil the solution. If the area under the cover should begin to dry out from overzealous heating a few additional drops of acetic acid may be introduced without issue.
Observe the slide under low power-a 10x objective and ocular will do.
Hemin crystals are elongated hexagonal crystals which will appear ruby colored under daylight corrected illumination. If the salt was not perfectly dissolved in the acetic acid the hemin crystals will be seen to form closely around the un-dissolved salt crystals. This makes for unattractive photomicrographs but has no negative impact on the results of the test. Let’s take a look:
So it would seem: YES! IT’S BLOOD!
If someone was going to aspire at being a sleuth they could prepare in advance a saturated solution of sodium chloride in acetic acid and cary it in a dropper bottle. To do so place 10ml or more of acetic acid in a test tube and introduce sodium chloride a few grains at a time while heating the test tube over a burner. Continue until a small amount of sediment is built up at the bottom of the tube. Allow the solution to cool and place into a stoppered dropper bottle.
In the field a scraping of the material to be tested is placed on a slip and a few drops from the bottle introduced to cover. Place a coverslip over the whole. One will still need to heat the solution to induce the formation of hemin crystals but something as pedestrian as a cigarette lighter will do the job. Observed with even an inexpensive field microscope the results will be obvious.