SULPHUR DIOXIDE AS A GERMICIDAL AGENT. 
« 
[By H. D. GecldingSj Parsed Assistant Surgeon. Acting Director Hygienic Laboratory, 
Marine-Hospital Service.] 
In considering the action of sulphur dioxide or sulphurous oxide as a 
disinfecting or germicidal agent, it is well possibly to begin with a brief 
review of the nature of the substance, its physical properties, and the 
method of its action. 
Sulphur dioxide, or sulphurous oxide, SO 2 , is the only compound of 
the combustion of sulphur in dry air or in oxygen gas. There are many 
methods of preparation, the easiest and most simple being jthe burning 
of sulphur in air. It may also be prepared by heating copper in a state 
of fine division as clippings or borings, with sulphuric acid, or by heat- 
ing sulphur in the presence of concentrated sulphuric acid. By either 
of these methods a liberal and x^ery regular evolution of the gas is 
obtained. 
Sulphur dioxide is a colorless gas having a peculiar suffocating odor. 
It instantly extinguishes flame and is totally irrespirable, therefore 
quickly destroying animal life. It has a density of 2.11 ; a liter weighs 
2.86 grams; 100 cubic inches weigh 68.69 grains. At about 4 atmos- 
pheres, or 60 pounds pressure, it can be reduced to a liquid, and at 
17.8° C. and at ordinary pressure it is reduced to a liquid condition, 
colorless, limpid, and very expansible by heat. Cold water dissolves 
more than thirty times its weight of the gas. Solutions containing sul- 
phur dioxide remain unchanged if excluded from the action of atmos- 
pheric oxygen, but when oxygen is present the liquid is rapidly oxidized 
into* a higher form, sulphuric hydrate, H. 2 SO^. In a dry state sulphur 
dioxide and oxygen gases may remain in contact for any length of time 
without change. 
Sulphurous acid, or sulphur dioxide, has active bleaching properties. 
It is used in the arts for bleaching woven goods and straw. A piece of 
blue litmus paper plunged into moist sulphur dioxide is at first 
reddened and then slowly bleaclied. In considering its action as a dis- 
infecting agent this bleaching property mu.st be borne in mind. 
The use of sulphur dioxide as a disinfecting agent dates back to a 
very remote period, far preceding that of the recognition of the bacte- 
rial origin of most contagious and infectious diseases, indeed, going 
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