An Exchange in Locard’s Own Words (Part 6)
||Richard E. Bisbing, McCrone Associates, Westmont, IL
Translated by Kathleen Brahney
Commissioned by McCrone Associates, Inc.
Doctor of Medicine, Professor of Law,
Director of the Lyon Laboratory of Police Techniques,
Vice-President of the International Academy of Criminology
Manual of Police Techniques
Third Edition, Completely Revised and Augmented
Paris: Payot, 16 Boulevard St. Germain, 1939
Part VI-Other Stains, Microchemistry and Starches
G. FOOD STAINS
On the clothing of the suspect or at the scene of a crime, one may
encounter diverse stains that could be confused with semen or pus, but which
are produced by digested food. Microscopic examination will allow one to
- Debris from meat:
muscle fibers, elastic fibers, conjunctive tissue.
- Debris from vegetables:
Grains of raw or processed starch; various plant cells
(polyhedral, spherical, spindle-shaped, star-shaped, aligned in rows);
vegetable fibers/hairs; spores.
containing many types of acids -- butyric, caproic, caprylic, capric, palmitic,
margaric, stearic, oleic -- which can be distinguished by their points of
fusion and by lecithins, with which one can determine the acids. All of these
stains are soluble in ether.
One can find sucrose or glucose. Only the latter will reduce Fehling’s liqueur
and will turn alkalis yellow.
In general, albuminoid material can be recognized in the following reactions:
- The Biuret reaction:
To an aqueous solution of the stain one adds two or three
drops of copper sulfate and a little bit of potassium. One will obtain a color
that varies, according to the nature of the albumin, from pure violet to
- The xantho-protein [sic] reaction:
Azotic acid [nitric acid] gives a yellow
coloration that darkens in the presence of ammonia.
- Adamkiewics’ reaction:
The stain dissolved in crystallizable acetic acid takes
on a slightly fluorescent violet tinge in concentrated sulfuric acid.
H. CANDLE STAINS:
These present themselves as brilliant white plates that are often
tear-shaped. The difficulty is to not confuse them with grease stains.
Confusion with semen, mucus or pus, however, is rarely possible.
Spots on clothing are removed by means of an extractor [solvent extraction].
Candle wax is formed in large part by stearic acid obtained by the saponification of fats
and suets using lime. Pure stearic acid is a solid white body, fusible at 68.38 degrees and soluble in alcohol and ether. The candle, being composed of impure stearic acid -- that is to say, not purified and still containing some fats -- has a fusion point between 51 and 58 degrees C. Its specific gravity is in the neighborhood of 0.850.
- Dosage of acidity:
Scrape about 4 grams of the wax stain into a glass with about 70 cc
of 95% neutral alcohol, dissolve it in a bain-marie and let it cool while
shaking it. Add a few drops of phenolphthalein and titrate it with 0.5N KOH
until there is a persistent pink color. The number of cc used, divided by 7.8,
indicates the weight of the fatty acids in the stearic acid contained in the
sample. Most of the time, the acid content thus obtained is between 95 and
- Fusion Point:
The point of fusion can be obtained as follows: Plunge a test tube
containing mercury into a beaker containing oil. On the surface of the
mercury, place a sample of the substance. Close the test tube with a cork that
has a precision thermometer through it; the thermometer should plunge into the
mercury. One heats this slightly with an alcohol lamp. When the specimen melts,
one notes the temperature. The fusion point should vary from 40 to 70 degrees C.
- Polarized Light:
Franz Dangl of Vienna used a microscope equipped with a
polarizing mechanism to analyze candle stains. “All substances, such as wax,
paraffin, stearine, ceresin, when placed between crossed Nicol prisms,
illuminate the field of the polarizing mechanism as long as the substances are
in a solid state. But they will obscure the field when they enter into fusion,
so that this important physical fact, from the point of view of fusion or
solidification, makes it easy to define [the substance] even when there are
only minimal traces of it. Moreover, a very small layer of a melted sample --
placed between the slide and the glass -- will present perfectly typical
structures in polarized light. In order to avoid variations due to a more or
less rapid degree of cooling, it is good to make strictly parallel
preparations, and to raise the temperatures of the two samples simultaneously
on the same heating plate, and then to let them cool down together, regularly
and rapidly. In this way, one can easily recognize their typical structures,
which will be easy to differentiate in polarized light.”
I. GREASE STAINS
Grease stains on clothing or linens may originate from food or from
various other contacts. One extracts them by means of an extractor.
Identification can be carried out using the following methods:
- Iodine index (Hubl’s method):
Prepare the five following liquids.
1 -- 25 grams of bisublimated iodine and 500 cc. of ethanol
2 -- 30 grams of HgCl2 and 500 cc. of ethanol
3 -- 24 grams 8 of Na2 S2O3, 5H2O, 1,000
grams of H2O; these are titrated
4 -- 10 grams of KI and 100 grams of H2O
5 -- 2% laundry starch
In an Erlenmeyer flask corked with emery [ground glass stopper], place about 0.3
grams of the substance to be tested. Add 10 cc of chloroform to dissolve it,
and 25 ml of a mix of liquids 1 and 2, in equal volumes. Leave these in
contact for 24 hours. Titrate the excess iodine. Introduce into the
Erlenmeyer flask 30 cc of liquid 4 and 100 grams of water. Put the titrated
solution of number 3 in the presence of the laundry starch; wait for complete
One will recognize the titrate of the iodo-mercuric solution; from the quantity of
iodine obtained using the above method one will extract a number which, when
adjusted for 100 grams of oil/grease, will be the iodine index.
- The Saponification Index (Koettstorfer‘s Index):
This is the number of milligrams of potassium needed to soponify 1 gram of fatty material.
In a 125-cc flask, place 3 to 4 grams of alcoholic potassium prepared as follows. In 200 cc
of pure alcohol, place 15 cc of 45% potassium washing powder; shake it hard;
filter off the insoluble carbonates; titrate 25 cc of this solution by means of
a liquid titrated with hydrochloric acid.
Let it “digest” in an ascending refrigerant [reflux] for a quarter of an hour. When
the saponification has taken place, one titrates the excess potassium with hydrochloric
acid. The difference between the two titrates, in relation to 1 gram of fatty
material, gives the saponification index.
- The Neutralization Index
This is the number of milligrams of potassium needed to
neutralize the free fatty acids contained in one gram of fatty material. If
the fatty material is liquid, the operation should be carried out cold; if the
material is solid, the operation should be carried out using heat.
Place 5 to 10 grams of fatty material in 50 cc of 95% alcohol. Shake it and titrate the 0.10
N potassium hydroxide with phenolphthalein.