The Chemical Warfare Service was able to develop an enamel and an oil paint which were very sensitive detectors of mustard gas. Both of these were yellow and became dark red in contact with mustard gas. The change was practically instantaneous. The enamel consisted of chrome yellow as pigment mixed with oil scarlet and another dye, and a lacquer vehicle, which is essentially a solution of nitrocellulose in amyl acetate. One gallon of this enamel will cover 946,500 sq. cm., or a surface equivalent to a band 3 cm. wide on 12,500 seven cm. shell. The paint was composed of a mixture of 50 per cent raw linseed oil and 50 per cent Japan drier, with the above dye mixture added to the required consistency. In contact with liquid mustard gas, this changes to a deep crimson in 4 seconds. Furthermore, in contact with arsenicals, this paint changes to a color varying from deep purple to dark green, the color change being almost instantaneous and very sensitive, even to the vapors of these compounds. Other substances have no effect upon the paint. For field work, however, nothing was found equal to the trained nose, and it is questionable if any of the mechanical means described will be used in the field. PHYSIOLOGICAL ACTION One of the most interesting phases of mustard gas is its peculiar physiological action. This has been studied extensively, both as relates to the toxicity and to the skin or blistering effect. TOXICITY When one considers the high boiling point of mustard gas, and its consequent low vapor pressure, he is likely to conclude that such a substance would be of comparatively little value as a toxic or poison gas. While it is true that an important part of the military value of mustard gas has been because of its vesicant properties, the fact still remains that it is one of our most toxic war gases. The following comparison with a few of the other gases indicates this: -----------------+---------------------- | Mg. per Liter +---------------+------ | Mice | Dogs -----------------+---------------+------ Mustard gas | 0.2 | 0.05 Phosgene | 0.3 | ··· Hydrocyanic acid | 0.2 | 0.1 Chloropicrin | 1.5 | 0.8 Chlorine | ··· | 3.0 -----------------+---------------+------ When an animal is exposed to the vapors of mustard gas in high concentration, it subsequently shows a complexity of symptoms, which may be divided into two classes: (1) The local effects on the eyes, skin and respiratory tract. These are well recognized and consist mainly of conjunctivitis and superficial necrosis of the cornea; hyperemia, œdema and later, necrosis of the skin, leading to a skin lesion of great chronicity; and congestion and necrosis of the epithelial lining of the trachea and bronchi.