Define Becke Line. Which direction does the Becke Line move when the particle is 1.49 and the oil used in 1.46?
Why? What are Cargille oils?
How are they used in forensics?
What would you do if you wanted to test for a refractive index between two oils?
How would identify its refractive index value?
The correct answer and explanation is :
Becke Line:
The Becke Line is a phenomenon observed in optical mineralogy and forensic science that occurs when a transparent particle is immersed in a liquid of a different refractive index. The Becke Line is a bright halo or line that appears near the edge of the particle when viewed under a microscope. It shifts towards the medium with the higher refractive index when the particle is moved in the direction of increased illumination.
Becke Line Movement (Refractive Index 1.49 and 1.46):
When the refractive index of the particle is 1.49 and the oil used has a refractive index of 1.46, the Becke Line will move towards the oil. This occurs because the oil has a lower refractive index than the particle, and when the oil is the surrounding medium, light bends towards the higher refractive index. As a result, the Becke Line moves outward, toward the oil, to align with the change in refractive indices. The particle has a higher refractive index, so it refracts light more strongly, creating the observed shift.
Cargille Oils:
Cargille Oils are specialized oils manufactured by Cargille-Sacher Laboratories, widely used in forensic analysis, mineralogy, and optical testing. These oils are chosen for their precise refractive index values, which can range from 1.30 to 1.81. Cargille Oils are commonly used in the process of determining the refractive index of small transparent objects, such as glass fragments or minerals, by immersion. They allow forensic scientists and mineralogists to match the refractive index of a particle with a specific oil, which is an important tool for identification purposes.
Use in Forensics:
In forensics, Cargille Oils are frequently used for the identification and comparison of glass fragments. By immersing a glass particle in an oil with a known refractive index, scientists can observe when the Becke Line disappears, signaling a match between the particle’s refractive index and that of the oil. This technique is particularly useful in cases of criminal investigations where glass fragments found at a crime scene are compared with suspected sources of glass.
Testing for a Refractive Index Between Two Oils:
To test for a refractive index between two oils, a forensic expert could use a technique called the “refractive index matching” method. By immersing the particle in a series of oils with known refractive indices and observing the movement of the Becke Line, the scientist can determine the refractive index value of the particle. The oil in which the Becke Line disappears corresponds to the refractive index of the particle. This helps forensic scientists accurately determine the refractive index of unknown glass fragments or other materials.