54 VETERINARY BACTERIOLOGY 



burned it yields sulphur dioxid, a gas that has been much used 

 in fumigation. It is powerless to destroy bacteria unless moisture 

 is present, with which it may unite and form sulphurous acid. 

 The latter is a very active bleaching and corrosive agent, hence 

 it should not be used except where it can do no harm. One 

 pound of water (about 1 pint) should be vaporized in a room 

 for every 5 pounds of sulphur burned. This amount should 

 efficiently disinfect 1000 cubic feet. Insects and other vermin 

 are destroyed by the sulphur fumes. 



Formaldehyd, HCHO. Formaldehyd is the gas used most 

 widely in fumigation and disinfection. It is very soluble in 

 water and is commonly sold as formalin, a 40 per cent, solution 

 of formaldehyd. Like sulphur dioxid, formaldehyd is efficacious 

 only in the presence of moisture, but, unlike it, does not bleach 

 fabrics or injure materials. Formaldehyd may be evolved in 

 gaseous form for disinfection in a variety of ways. Incomplete 

 combustion of methyl alcohol according to the reaction 



2CH 3 OH + 2 = 2HCHO + 2H 2 O 



is utilized in a number of lamps upon the market. When properly 

 carried out the method may be efficient, but it has several 

 disadvantages, i. e., expense and presence of a fire in a closed 

 room. Heating the formalin over an open flame will liberate a 

 part of the formaldehyd readily, but under these conditions 

 it polymerizes and some of the polymers (paraformaldehyd) are 

 insoluble. If the evaporation is continued to dryness, all of these 

 will again be broken up and given off as formaldehyd. The 

 same result can be reached more quickly by the addition of glyc- 

 erin or some salt which will raise the boiling-point of the solu- 

 tion above the dissociation temperature of the paraformaldehyd. 

 An autoclave or closed vessel in which the solution is heated con- 

 siderably above the boiling-point of water will serve the same pur- 

 pose. Twelve ounces of formalin should be used for every 1000 

 cubic feet to !><> fumigated. A convenient method for fumigating 

 small rooms is to pour formalin over crystals of potassium per- 

 manganate in an earthen vessel that is a poor conductor of heat. 

 The permanganate is an active oxidizing agent and converts part 

 of the formaldehyd into carbon dioxid and water, with the 



