620 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
TasLe [.—Lethal dose, 
{January to March, 1910.] 
Parts of Duratian| 
Animals. ozone per of Result. 
miilion. | exposure. 
| — 
HH. m. 
Pals GES ai as sd a ne eens 15 34 0 | Died following night, tung showing pneumonia. 
DO sesso esas: svete ceo ssees 2 32 0 | No ill efiecis. 
DO es seecte ema stacenceeeaos 3-5 32 0 Do. 
Direitsali cater sah o- eseeecsae ee 7% 3? 0 | Rats quiet, fur standing up; recovered. Cat killed 
next day; signs of lung irritation. 
adorns mats ss.028 52 ss eee heen 10-20 2 0 | Disordered breathing of al] animals; all recovered. 
PiSORLSE oe enon cine He's Aa Selene 94 34 0 | Jerky breathing; soon recovered. 
1B) OS eee eee eee 7 33 0 | Dyspnoeic; 1 had snufiles; soon recovered. 
WGOEtOMASe cine cece ences 113 22 0 | Dog’s breath disordered; developed cough and bad 
breathing 1 hour after; all eventually recovered. 
DESL OYE) SC alos ae Ee, Oe ek wy A gi 3 5] Depressed; breathing disordered; moist sounds; 
recovered. 
OU riEy Rohs aac. ek tS A i tele i a 10 4 0] Furrufled; recovered. 
ret base es Sy eee iste BEL oe 11 2 0] No permanent ill effects. 
PMOUSC rect eee (eee Sone 20 2 0] Died; pneumonic signs found post mortem. 
ID) Os eeeeeisie cae en ieee 40 1 0] Very disordered breathing; eventually recovered. 
On breathing two to three parts per million, we ourselves find it 
irritating to the respiratory tract, with a tendency to produce, in this 
concentration, headache and oppression. The irritation set up by 
ozone, together with its strong characteristic smell, affords ample 
warning, and would prevent anyone exposing himself unintentionally 
to a dangerous concentration. The irritation set up would naturally 
make anyone remove himself from the influence of the ozone before 
any serious damage to the lungs had been set up. As far as we can 
see, then, no serious risk can arise from the use of ozone generators 
so long as the generators are not placed in a confined space from which 
escape is impossible. 
It is only possible to estimate concentrations of much less than one 
part of ozone per million parts of air by passing very large quantities 
of the ozonized air through the acidified potassium iodide solution. 
We find concentrations of far less than one in a million parts can be 
both smelled and tasted; the physiological test for ozone therefore is 
extraordinarily delicate. If ozone is used in a ventilating system, 
we think it should be in such concentration as is scarcely perceptible 
to a keen sense of smell. 
Ozone has most potent action as a deodorizer. We tested this by 
filling our experimental chamber with the smoke of shag tobacco, 
ammonium sulphide, or carbon bisulphide vapor. At other times 
we placed in the chamber stinking meat, or human feces. After 
putting in action the two small ozonizers, placed in the roof of the 
chamber, for two minutes, we were not able to detect the odors of 
