PARA-DICHLOROBEXZEXE AS AN INSECT FUMIGANT. 7 



(1) By the action of chlorine on benzene (C 6 H 6 ) in the presence of iodine. A little 

 ortho-dichlorobenzene is also formed in this reaction. 



(2) By the action of phosphorus pentachlorid on para-chlorophenol. 



(3) By the action of phosphorus pentachlorid on para-phenolsulphonic acid. 



He gives the melting point of this compound as 53° C. (127.4° F.) and its boiling 

 point as 172° C. (341,6° F.), but quotes Mills (Phil. Mag. (5) 14, 27) as giving 52.72° C. 

 for the melting point. 



Para-dichlorobenzene crystallizes from alcohol in monoclinic leaves, it sublimes at 

 ordinary temperatures, is soluble in hot alcohol in all proportions, and is easily solu- 

 ble in ether, benzene, carbon bisulphid, etc. 



In regard to physiological properties, Francis and Fortescue-Brickdale x state: 



The benzene halogen derivatives have a slight odor, are insoluble in water, vola- 

 tilize without decomposition, and are very stable. * * * Corresponding to their 

 stability it is found that the halogen is not split off in the organism, and that they 

 do not show hypnotic properties. With the entrance of chlorine the antiseptic prop- 

 erties increase * * * Chlorbenzene acts on the spinal cord to a greater extent 

 than benzene. 



The following figures in regard to para-dichlorobenzene are from calculations made 

 by R. C. Roark: 



Molecular weight 146.952 



Density of the vapor 4.592 if oxygen equals 1. 



72.892 if thydrogen equals 1. 

 5.1025 if air equals 1, assuming the mo- 

 lecular weight of air to be 28.8. 



In other words, assuming no dissociation or association, a given volume of para- 

 dichlorobenzene in the form of a vapor would be 5.1025 times as heavy as an equal 

 volume of air at the same temperature and at the same barometric pressure. 



The vapor of para-dichlorobenzene will flash at about 70° C. (158° F.), but even 

 when held in a very hot flame and ignited the substance will not continue to burn 

 after the flame is removed. Thus the substance is not combustible, but is decom- 

 posed by heat into substances which partially burn with copious deposition of soot 

 when directly in a flame. 



As the vapor pressure of para-dichlorobenzene has never been determined, it is 

 impossible to state how much of its vapor air at any temperature short of 172° C. 

 (341.6° F., its boiling point) would take up. At 172° C. (341.6° F.), barometer 760 

 mm., 1 liter of para-dichlorobenzene gas would weigh 4.0257 grams, or 1 cubic foot 

 would weigh 4.0208 avoirdupois ounces. 



•Francis, Francis, and Fortescue-Brickdale, J. M. The Chemical Basis of Pharmacology, p. 99, 

 Eondon, 1908. 



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