130 Milk and ‘Its Products 
line, titrate against one-twentieth normal hydrochloric 
acid, using litmus as its own indicator. (Litmus is 
blue when alkaline and red when acid.) The neutral 
point will be recognized by the blue solution turning 
reddish. If the neutral point of the solution using 
phenol phthalein as an indicator is zero, then the 
neutral point using litmus as an indicator would 
require 2.5 ¢. c. more acid. Therefore, in order to 
secure 1 per cent acidity to phenol phthalein, 5 c¢.c. 
of the litmus solution would require 1.5 c.c. of 
twentieth normal hydrochloric acid. As the litmus 
solution is always alkaline, it will require normal acid; 
the amount can be determined in the same way as in 
titrating media. Sterilize litmus the same as water. 
Normal sodium hydroxid (NaOH) and normal hydro- 
chloric acid (HCl) .—These solutions had best be bought 
from dealers. To make twentieth normal solutions, one 
part of the normal is added to 19 parts of distilled water. 
Sterilization.—In bacteriological work, it is neces- 
sary to have all glassware, utensils and media sterile, 
that is, absolutely free from organic life. It must be 
remembered that media, bottles, flasks, etc., must be kept 
plugged, otherwise they become contaminated. There- 
fore, if a flask or bottle of media or water is opened, it 
must be resterilized before using again. The methods 
of sterilizing vary for the materials to be sterilized. 
Cleaning glassware.—All glassware should be thor- 
oughly washed with some good soap or soap powder, 
rinsed in clear water, and allowed to drain. When 
dry, the test tubes, pipettes, flasks and graduated 
cylinders are ready to be plugged. With the forceps, 
