10 
LABORATORY MANUAL 
EXERCISE NO. 5 
Object: To become acquainted with methods of etching and labeling glass¬ 
ware. 
Procedure: All newer glassware has a space provided on the bulb for 
writing. However, it is sometimes desired to etch numbers 
on glassware or to produce roughened surfaces for writing. 
This may be done as follows: 
The student should familiarize himself with at least two 
methods. 
A. Take a piece of paper of the desired shape and stick it on the 
bottle over the spot to be etched. Immerse the bottle in hot 
paraffin. Remove the paper by cutting the paraffin around it. 
Place etching solution on the exposed surface for 20 seconds to 
1 minute. Wash off the solution and try to write on the sur¬ 
face. If unsatisfactory, repeat the treatment. A number may 
be etched on the bottle by merely scratching the number 
through the paraffin. 
B. Prepare surface to be etched as indicated under “A” above. 
Place some calc um Flouride in a lead dish. Add enough 
sulfuric acid to form a paste. Allow the fumes to come in con¬ 
tact with the exposed glass surface, or spread a small quantity 
of the paste over the exposed surfaces. 
Note: Whenever hydroflouric acid is produced, the process 
should be carried on under a hood or at an open window. 
C. A rough surface may be produced on glass by using a fine steel 
file, dipped in water, and passed over the surface to be rough¬ 
ened, several times. 
D. There are two commonly used methods for protecting labels 
on reagent bottles: 
(1) Use a good mucilaged label and on it write the desired 
information with India ink. Place the label on a pre¬ 
viously cleaned surface of the bottle, and when dry, 
paint the labeled part entirely with very hot paraffin, 
or dip the labelled part in paraffin. 
(2) Proceed as under “1” above, but cover the labelled area 
with shellac. 
Observation: Record time required for the solution to act. 
Conclusion: 
Questions: (1) Give a definition for legal milk in this state. 
(2) Of what is the ash of milk composed? 
(3) What is meant by the term vitamines, and state briefly how 
milk compares with other foods in vitamine content. 
(4) What is colostrum milk? How does it differ from normal milk? 
References: F. & W. U 20, 23; Van S. pp. 1-19; Jud. pp. 22-28; St. 
pp. 28-29; 37-38. 
