136 STERILIZATION AND DISINFECTION 
Chloride of lime is soluble according to Hooker (1913) in about 2% 
times its own weight of water. It leaves an insoluble residue com- 
posed mostly of calcium hydroxide. It is prepared from Ca(OH)2 as 
follows: 
OH HCl re 
CaC 4 = Ca + 2H20. 
OH HOC! Oc! 
The HOCI is made by treating water with chlorine. Some care 
should be used to secure clear solutions for use in disinfection. This is 
especially true in water treatment. The potential part of this com- 
pound is very soluble in water while the part with no sterilizing 
properties quickly settles out. Hooker (1913) gives the following rules 
for the use of chloride of lime: 
First, do not mix too stiff a paste, otherwise a gelatinizing action takes place 
and greater difficulty in settling out is encountered. Never mix a paste with 
less than 4 gal. of water for 1 Ib. of chloride of lime. Second, it is not necessary 
nor desirable to grind nor break up the lumps too thoroughly; the available 
chlorine nearly all dissolves readily and too much agitation is detrimental to 
prompt settling. 
The above precautions should be borne in mind in any application 
of chloride of lime to sanitation. 
The strength of chloride of lime is measured in terms of “‘ available 
chlorine.”’ This is an unfortunate term since it implies that the dis- 
infecting properties of the compound rest in the chlorine. The work 
in the past indicates that it is an oxidation and not a chlorination. 
The oxygen is formed in the following manner: 
Ca(OCl)2-+- H2CO3 = CaCO3-+2HCIO. 
2HCIO = 2HCI+ Oe 
It has been suggested by some sanitarians that the term “ available 
chlorine ’”’ be substituted by the term “ potential oxygen.” Lager (1916) 
has made some interesting statements in regard to the action of calcium 
hypochlorite. He states that the disinfecting action does not depend 
upon the available chlorine nor the length of time the chlorine acts. 
He states that the time for killmg depends upon the resistance of the 
organism. 
The United States Pharmacopoeia specifies that chloride of lime shall 
contain 35 per cent of available chlorine. As it is purchased in small 
cans on the open market it probably falls far short of this and the use 
