168 STERILIZATION AND DISINFECTION 
Phenol crystals themselves as well as solutions change in germicidal 
strength upon standing, particularly when exposed to direct sunlight, 
and to high temperature. Phenol changes more readily when melted 
or in the presence of moisture than when in crystalline form. It is 
important, therefore, that the crystals of phenol be kept in a tightly 
stoppered bottle, in a cool, dry place and exposed to the light and mois- 
ture as little as possible. Phenol which has been exposed to the air and 
allowed to absorb enough water to alter its melting-point or which has 
become at all red should be discarded for the purpose of this test. The 
5 per cent stock solution is prepared as follows: Melt the phenol in the 
original container and pour out approximately 50 gms. into a closed 
weighing bottle; weigh and dissolve in the proper amount of water to 
give a 5 per cent solution. Do not attempt any further standardization. 
This stock solution is kept in the refrigerator in ambered-colored bottles 
of not more than 500-c.c. capacity, and for a period of not longer than 
three months. 
Dilutions, Distilled Water. Sterile distilled water is recommended 
for all dilutions. Attention is directed to the danger of metallic copper 
in the distilled water prepared from the common type of laboratory 
still in which the condensation surface is of tin-coated copper or brass. 
If the tin-plate is worn away sufficient copper may be dissolved to 
materially influence the coefficient. 
Five Per Cent Stock Solution. Accurately graduated capacity 
pipettes are to be used in preparing the stock dilution of disinfectant. 
Five c.c. of disinfectant are measured into a flask containing 95 c.c. of 
sterile distilled water the interior of the pipette being rinsed several 
times with the contents of the flask. From this solution or emulsion, 
and from the stock 5 per cent phenol solution the required dilutions are 
prepared. 
Initial Dilution from 5 Per Cent Dilution. Take 50 c.c. of the 5 
per cent stock solution, place in a 100-c.c. graduated flask and make 
up to the mark with sterile distilled water. Mix by pouring. This 
gives a dilution of 1: 40. With 50c.c. of this dilution repeat the process 
to obtain a dilution of 1 : 80 and so on by successive dilutions until the 
following initial dilutions or such as these as are necessary for the test, 
are prepared: 
1: 20 1: 160 
1:40 1 : 320 
1: 80 1 : 640 
Final Dilutions from Initial Dilutions. With sterile delivery pipettes 
measure the quantities of initial dilutions and sterile distilled water 
