ForChem

• Areas within Forensic Chemistry

  • Legal medicine
  • Ballistics
  • Questioned documents
  • Dactyloscopy
  • Photography
• Scientific Evidence


  Means sanctioned by law, of ascertaining in a judicial proceeding the truth respecting a matter of fact wherein scientific knowledge is necessary
• Scientific Evidence is a proof of allegation
• Physical Evidence


  Evidence that the senses perceive
• Scientific Evidence is an article and material which is found in connection with an investigation and which aids in establishing the identity of the perpetrator or the circumstances under which the crime was committed or which in general assist in the prosecution of the criminal
• Circumstantial Evidence


  Kind of evidence which seeks to establish a conclusion by inferences from proved facts
• Direct evidence


  Statement made by a witness based on what he saw, heard, smelled, touched, or tasted
• Exceptions for admissibility of Hearsay Evidence

  • Declaration against interest
  • Dying declarations
  • Res gestae
  • Reputation
  • Public Records
  • Statements made at a prior time
• Indirect evidence


  Statement made by a witness on the authority of another and not from his own personal knowledge or observation
• Real or Autoptic Evidence


  Evidence addressed to the senses of the court
• Testimonial Evidence


  Expert placed on the witness stand to answer all questions propounded by both parties in the case
• Practice of Forensic Chemistry

  1. Whenever possible, the chemist should personally collect all specimens necessary for the examination

  2. Principles observed during specimen collection: sufficiency of samples, standard for comparison, maintenance of individuality, labelling and sealing
• Forms of Scientific Evidence

  An expert witness may be required to perform certain experiments to prove a certain matter of fact
• Witness


  • One who testifies in court and has personal knowledge or experience
  • A person other than the suspect who is requested to give information concerning an incident or person
• Practice of Forensic Chemistry

  Results will be communicated to the requesting party in the form of a written report which must include an enumeration of the articles received for examination with detailed description of the packing, sealing and labelling, date of receipt and from whom received, the purpose of examination, the findings and conclusion
• Six Golden Rules in the Practice of Forensic Chemistry


  • Good work cannot be hurried, therefore take all the time necessary to make the case complete, no matter how urgent it may appear or how pressing others may be of the result
  • Make careful and minute examination of everything and do not be satisfied with a qualitative analysis if a quantitative one is possible; it always pays to do too much rather than too little and it is difficult to foresee what will or will not be required in court
  • Keep a full, neat and clear record of everything seen and done
  • Many cases will lead the expert into paths with which he is not familiar, and when this happens, he should consult others who are most likely to know
  • This enables inferences and deductions to be made from slender and incomplete premise is often very useful
  • The simplest explanation is usually the right one
  • Avoid complicated theories
• Forms of Scientific Evidence

  1. An expert may be placed on the witness stand and answer all questions to be propounded by both parties in the case

  2. Solemn declaration made orally by a witness under oath in response to interrogation by a lawyer
• Total magnification

  • 10x ocular, 4x red objective = 40x
  • 10x ocular, 10x yellow objective = 100x
  • 10x ocular, 40x blue objective = 400x
• Benefits of Light Microscopes

  • Smaller and portable
  • Cost-effective
  • Easy specimen preparation
  • Training simple and user-friendly
  • Can see microscopic items
• General Procedures on how to use a microscope

  1. Make sure all backpacks and materials are out of the aisles and off the tops of desks

  2. Store with cord wrapped around microscope and the scanning objective clicked into place

  3. Carry by the base and arm with both hands
• Types of objective lenses

  • Scanning
  • LPO (Low Power Objective)
  • High (High Power Objective)
  • Oil Immersion
• Important properties of Microscopes

  • Magnification - the power of the microscope to enlarge the image of an object
  • Resolution - the power of the microscope to show detail clearly
• Parfocal


  Microscopes can switch between lenses without much adjusting
• Only use lens paper to clean objectives
• Before the microscope, no one knew about the microbial world
• Anton Van Leeuwenhoek perfected lenses for the microscope
• Focusing Specimens

  1. Start with the Scanning Objective

  2. Place specimen in the center of the field of view

  3. Use the Coarse Knob to focus

  4. Use the Fine knob for fine focusing

  5. Switch to Low Power and repeat focusing steps

  6. Switch to High Power for further focusing
• Types of Light Microscope

  • Simple - Has one lens (e.g., magnifying glass, Leeuwenhoek’s microscope)
  • Compound - Has 2 or more lenses (e.g., High school Biology microscope)
• Storing a microscope

  1. Store with cord wrapped around microscope and the scanning objective clicked into place

  2. Carry by the base and arm with both hands
• If you use the coarse knob under high power, the slide or lens could crack
• Leeuwenhoek was the first to see living cells
• Inverted image


  The image appears upside down and backward compared with the actual object
• Hooke coined the term cell while viewing cork
• Schleiden determined that all plants and their parts are composed of cells
• Recap of focusing steps

  • Scanning --> use coarse and fine knob
  • Low power --> use coarse and fine knob
  • High power --> use fine knob only
• Making a Wet Mount Slide

  1. Get a clean slide and coverslip from your teacher

  2. Place ONE drop of water in the middle of the slide

  3. Place the specimen into the water

  4. Place the edge of the coverslip on one side of the water drop at a 45° angle

  5. Slowly lower the coverslip on top of the drop. THIS PREVENTS AIR BUBBLES
• Lamarck, Mohl, and Meyen indicated the cellular nature of life
• Moving the slide in the opposite direction

  The image appears to move in the opposite direction
• Schwann determined that all animals and their parts are composed of cells
• Cell Theory: All living things are composed of cells, cells reproduce or come from pre-existing cells via cell division (mitosis), cells are the basic units of life or the smallest form of life