Mustard gas is a high boiling and very persistent material, which is characterized by its vesicant (skin blistering) action. Men who come in contact with it, either in the form of fine splashes of the liquid or in the form of vapor, suffer severe blistering of the skin. The burns appear from four to twelve hours after exposure and heal very slowly. Ordinary clothing is no protection against either the vapor or the liquid. Other effects will be considered in Chapter IX. Since then there has been no important advance so far as new gases are concerned. Various arsenic derivatives were prepared in the laboratory and tested on a small scale. The Germans did actually introduce ethyldichloroarsine and the Americans were considering methyldichloroarsine. Attempts were made to improve upon mustard gas but they were not successful. LEWISITE It is rather a peculiar fact that so few new chemical compounds were used as war gases. Practically all the substances were well known to the organic chemist long before the World War. One of the most interesting and valuable of the compounds which would have found extensive use had the War continued, is an arsenic compound called Lewisite from its discoverer, Capt. W. Lee Lewis, of Northwestern University. The chemistry of this compound is discussed in Chapter X. Because of the early recognized value of this compound, very careful secrecy was maintained as to all details of the method of preparation and its properties. As a result, strange stories were circulated about its deadly powers. Characteristic of these was the story that appeared in the _New York Times_ early in 1919. Now that the English have published the chemical and pharmacological properties, we can say that, although Lewisite was never proven on the battle field, laboratory tests indicate that we have here a very powerful agent. Not only is it a vesicant of about the same order of mustard gas, but the arsenical penetrates the skin of an animal, and three drops, placed on the abdomen of a mouse, are sufficient to kill within two to three hours. It is also a powerful respiratory irritant and causes violent sneezing. Its possible use in aeroplane bombs has led General Fries to apply the term “The Dew of Death” to its use in this way. CAMOUFLAGE GASES Considerable effort was spent on the question of camouflage gases. This involved two lines of research: (1) To prevent the recognition of a gas when actually present on the field, by masking its odor. TABLE I CHEMICAL WARFARE GASES