UNITED STATES DEPARTMENT OF AGRICULT 
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DEPARTMENT BULLETIN No. 1389. 
February, 1926 
Washington, D. C. 
DETERIORATION OF COMMERCIALLY PACKED CHLORINATED LIME 
By C. C. McDonne tu, Senior Chemist, and Lresyiz Hart, Assistant Chemist, 
Insecticide and Fungicide Laboratory, Miscellaneous Division, Bureau of 
Chemistry 
CONTENTS 
Page Page 
mrnoge of investifation.._...-.......------.--- Fat) SISCUSSION OF TESULIS > es Ere ee ee 14 
Results of previous investigations_-_--..--.----- 2 | UMAR Y <<<. TELS IEE ETS es ey OS 18 
Sutline of investigation--...-__.---=---.------- As) iterate Cited235 25.04 2 ea eas ee 19 
eee OF investigation__..—.-2>--2=--.-c-==2.- Pf 
PURPOSE OF INVESTIGATION 
Chlorinated lime, sometimes called ‘bleaching powder” or im- 
properly “‘chloride of lime,” is extensively used as a bleaching agent 
and as a germicide and deodorant. Although the chemical com- 
position of this substance has not been definitely determined, it is 
generally considered that the active constituent is calcium oxy- 
chloride, according to Odling’s formula, Ca os , accompanied by 
1 
calcium chloride and free lime in varying quantities. The chemistry 
of hypochlorites is fully discussed by Lunge (4).1 
The activity of chlorinated lime as a bleaching agent or as a dis- 
infectant is expressed in terms of the “available chlorine” content. 
Hooker (3) defines this as ‘‘the whole amount of free chlorine that 
becomes available in decomposing chlorinated lime with strong acid.” 
Despite the use of the term ‘available chlorine,” the activity of 
chlorinated lime as a germicide or deodorant is commonly believed 
to depend not on its chlorinating but on its oxidizing power (3). 
The carbon dioxide of the air and possibly weak organic acids con- 
tained in tap water or in soil liberate free hypochlorous acid, which 
is held to be the active oxidizing agent of chlorinated lime. This 
acid gives up its oxygen very rapidly, as may be expressed by the 
equation HCIO=HCI+0. Nascent oxygen so formed decomposes 
most organic matter with which it comes in contact. 
The fact that the strength of chlorinated lime decreases with age 
has long been known. Since its activity as a germicide is in pro- 
portion to its available chlorine content at the time of use, this 
deterioration is very important to consumers, who not only suffer 
a monetary loss when they fail to get what they pay for but also find 
the product ineffective as a germicide. In the false security given 
1Italic numbers in parentheses refer to ‘‘ Literature cited,’”’ p. 19. 
69575°—26t——1 
