I have a theory about how to prove it or not, however it's not really using forensics. Take the powder to a drug sniffing dog and let the dog get a scent, if it is drugs you'll know from the dog.
Good idea, but not enought time to get a drug sniffing dog to the evidence, and a hit from a drug sniffing dog is usually enough for a search warrant, not charging purposes to put someone in jail. Good thinking though.
Density of drug powder wouldn't be very useful, since it is usually cut with other substances at highly variable percentages. For the same reason, refractive indices could possibly be useful, depending on the substance and purity. In this case, we assume a non-pure substance. Good thinking.
Furthermore, in order to establish its identity , its physical properties have to be determined. Once that's done, it must be screened with these five color tests( Marquis, Dillie-Koppanyi, Duquenois-Levine, Van Urk and Scott) and then a single test to confirm it; then it is tested for identification by the color and shape of its crystals, followed by Chromatography , Spectrophotometry and Mass Spectrometry.
Pretty much nailed it, although I disagree that it must be screened with those five color tests, and all of the remaining tests you listed, especially since the Duquenois test is only used on marijuana, not a white powder. Certainly what MUST be done to test is based on an individual lab's procedures, but it is generally accepted to have to identify an unknown substance with two tests - the second being a confirmation test. If this were me in this scenario I would do a Liberman's test, and then either a Marquis or a Scott's test depending on the result of the Liberman's. Then based on the second color test, I would perform two micro-crystaline tests to identify/confirm the unknown substance. Total time to do the analysis, including note taking and weighing the substance would be about 5 minutes. OK. I'll think of another scenario and post tomorrow.
Lieberman's test is a general test for alkaloids. It's basically concentrated sulfuric acid with sodium nitrite. It reacts with most common controlled substances, but the color changes are generally pretty subtle and similar. So it's a good first test to differentiate between cocaine and methamphetamine for example, but the color differences are generally only in the range of yellow - orange - red.
The Hit and Run A car is pulled over on the side of the road while the driver is out changing the driver's side rear tire. The driver's wife is in the car since it is at night (approximately 1100) and cold. Suddenly a vehicle swerves over and hits the man changing the tire. The vehicle continues on its way. The wife still in the car notes the type of vehicle, and a partial license plate before dialing 911. Police and emergency crews arrive shortly, and the man is taken to the hospital where he dies shortly thereafter. The wife describes the vehicle and partial plate. One of the officers recognizes the description as probably belonging to "ol' Barney", a well known patron of Moe's Tavern. The police arrive at Barney's house approximately an hour later, and find Barney at home watching TV, drinking whiskey. Looking at Barney's car which is parked in the driveway, they notice some blood on the front passenger side fender. Barney is arrested for the accident. The local law jurisdiction requires that in order for aggravating circumstances, Barney must have been at least a 0.150 g/100 ml alcohol concentration in order for a vehicular homicide charge. If not, Barney will only be charged with manslaughter/fleeing the scene of an accident/crime. This is not Barney's first run in with the police. He refuses any statements about what he has or has not had to drink or eat. He refuses to perform field sobriety testing and to provide a breath sample. About an hour after police arrived at Barney's house a search warrant is obtained and police forcibly draw blood from a resisting Barney. You are the forensic scientist assigned to case and a few days later you obtain results of 0.140 g/100 ml for Barney at the time of the draw. While you are on the stand in court, the prosecutor is asking you perform a retrograde extrapolation to determine what Barney's alcohol concentration was at the time of the accident, so they he can be charged with the more serious vehicular homicide charge. Your response is... Please explain what things you assume, what elimination rates you might use, and what equations you use.
Well, as the hit-and-run takes place in the U.S., I would use the unit percent weight per volume equation, i.e. % w/v. The elimination rate, bevause it varies from individual to insdividual, would be between 15 and 30 percent w/v per hour.
OK. But you already determined the concentration at the time of the draw to be 0.140 g/100 ml (which is % w/v). What would you do to answer the prosecutor's question?
I would show him a chart showing him the Blood alcohol in terms of milligrams per 100 ml and percentage by weight over a period of hours.
Take a whiff and see what happens. :lol: JK. What is this? The set of The Simpsons? (JK, but it is weird) Ah we have to do a explantion in the court room? Argh, i hate lawyers. I wish i didn't miss out on the *mysterious* white powder. Tell the jury that he simply wasn't drunk enough. I'm guessing Barny is a big guy, and since he's a regualr customer at Moe's, it's probably going to be difficult for him to get hammered. Maybe the victim was on his bad side? Owed money? Drugs?
OK. So let's say you have such a chart. What assumptions are you making before you even show the chart?