Protection Against Smoke
While the charcoal and soda-lime granules furnished an adequate protection against all known true gases, they did not furnish protection against certain smokes or against minute particles of liquid gas. Since certain smokes, as stannic chloride, though not deadly, are so highly irritating as to make life unbearable, it early became necessary to devise means for keeping them from going through the masks. This was done in the first masks by adding a sufficient thickness of cotton batting. The cotton was usually placed in three layers alternating with the charcoal and granules, as it was thought the latter would be held in place better by that means.
Some time after stannic chloride came into use the Germans started firing shells containing a small quantity of diphenylchloroarsine, popularly known as “Sneezing Gas.” Protection against this is discussed in [Chapter XVIII].