1 68 THE NEW WORLD OF SCIENCE 



In the earlier man tests the men were sent inside a gas 

 chamber; but afterwards the canisters were connected by tubing 

 to the gas chamber and the men sat outside the chamber. This 

 made it possible to run more tests simultaneously and had the 

 further advantage that the man in charge of the testing could 

 determine for himself whether any given canister had broken 

 down or whether the report was due to nervousness on the part 

 of the subject. All the toxic gases can be detected at concen- 

 trations which do no harm to the individual. There are two 

 extremes to be guarded against. The man who is testing the 

 canister may imagine that gas is coming through when that is 

 not the case, or he may be so anxious to avoid giving a false 

 report as to continue the test too long and consequently get 

 gassed slightly. With the men accessible outside the chamber, 

 it is a comparatively simple matter to guard against both these 

 possibilities. 



The man test is only run until gas is detected coming through 

 the canister; but the machine test can be run farther. It is 

 customary to designate the time at which gas can be detected 

 coming through the canister as the " breakdown." Up to then 

 all the gas was removed by the materials in the canister. The 

 99 per cent., 95 per cent., 90 per cent, points, etc., are the points 

 at which 99 per cent., 95 per cent., 90 per cent., etc., of the gas 

 is stopped and I per cent., 5 per cent., 10 per cent., etc., of the 

 gas in the air comes through. 



When testing the variations in absorbents, the absorbent is 

 filled into a sample tube, of specified diameter, to a depth of 

 10 cm. by the standard method of filling, and gas passed 

 through under definite conditions. 



Trained observers can detect mustard gas by smell at o.i p.p.m. 

 (0.0007 m - P er liter) ; but only for the first minute or two of 

 exposure. Low concentrations of mustard gas vapors, when 

 in contact with a dilute solution of selenious acid, produce an 

 orange-colored colloidal suspension of selenium which gradu- 

 ally increases to a deep brick-red color in time if the concen- 

 tration of mustard gas is sufficient. The test is sensitive to 



