The law loves science. It doesn’t really understand science, and certainly can’t tell valid science from junk, but it loves that it removes the human variable and shifts responsibility off of untrustworthy human sensibilities and onto something irrefutable. We want proof so that nagging sense that we could be wrong will be eliminated, and science gives us that. All for $2, which is a pretty good deal.
Field testing for narcotics is an improvement over guessing, which was the way it was done before. Not perfect, but certainly better than leaving it up to a cop’s “training and experience.” And so, a test kit was developed that would fall far short of perfect, but better than “it looked like drugs to me.”
The test . . . involves dropping a suspected drug sample into a vial of cobalt thiocyanate, which is supposed to turn blue in the presence of cocaine. But as Gabrielson and Sanders note, “cobalt thiocyanate also turns blue when it is exposed to more than 80 other compounds, including methadone, certain acne medications and several common household cleaners.” That is not the only cause of false positives:
Other tests use three tubes, which the officer can break in a specific order to rule out everything but the drug in question—but if the officer breaks the tubes in the wrong order, that, too, can invalidate the results. The environment can also present problems. Cold weather slows the color development; heat speeds it up, or sometimes prevents a color reaction from taking place at all. Poor lighting on the street—flashing police lights, sun glare, street lamps—often prevents officers from making the fine distinctions that could make the difference between an arrest and a release.