Mustard gas melts, when pure, at 13° to 14° C. (The ordinary summer temperature is 20°-25° C.). The ordinary product, as obtained from the “reactor,” melts from 9°-10° C. In order that the product in the shell might be liquid at all temperatures, winter as well as summer, the Germans added from 10 to 30 per cent of chlorobenzene, later using a mixture of chlorobenzene and nitrobenzene and still later pure nitrobenzene. Carbon tetrachloride has also been used as a means of lowering the melting point. Many other mixtures, such as chloropicrin, hydrocyanic acid, bromoacetone, etc., were tested, but were not used. The effect on the melting point of mustard gas is shown in the following table: MELTING POINT OF MUSTARD GAS MIXTURES ---------+--------------+---------------+--------------- Per Cent | Chloropicrin | Chlorobenzene | Carbon Added | | | Tetrachloride ---------+--------------+---------------+--------------- 0 | 13.4° C. | 13.4° C. | 13.4° C. 10 | 9.8 | 8.4 | 9.8 20 | 6.3 | 6.4 | 6.6 30 | 2.6 | -1.0 | 3.1 ---------+--------------+---------------+--------------- The mustard gas as finally made by the United States contained about 17 to 18 per cent sulfur in solution. The gas was then put in shell and fired without the addition of any solvent. In actual practice this impure product seemed even more powerful in causing casualties than equal quantities of the pure mustard gas. Accordingly no redistilling as originally contemplated was actually carried out. The specific gravity of mustard gas at 20° is 1.2741. The solid material has a slightly higher value, being 1.338 at 13°. Its vapor pressure at room temperature is very low; at 20° this value has been found to be about 0.06 mm. of mercury. Mustard gas is practically insoluble in water, less than 0.1 per cent forming a saturated solution. The reports that a 1 per cent solution could be obtained did not consider the question of hydrolysis. Mustard gas is freely soluble in all the ordinary organic solvents, such as ligroin, alcohol, ether, chloroform, acetic acid, chlorobenzene, etc. In case the solvent is miscible with water, dilution throws out the product as an oil. CHEMICAL PROPERTIES Mustard gas is very slowly decomposed by water, owing to its very slight solubility. The products are dihydroxyethylsulfide and hydrochloric acid: (ClCH₂CH₂)₂S + 2H₂O = (HOCH₂CH₂)₂S + 2HCl Certain sulfonated oils accelerate the rate of hydrolysis, both by increasing the rate of solution and the solubility of the mustard gas. Alkalies also increase the rate of hydrolysis. Oxidizing agents destroy mustard gas. This reaction was made use of practically in that solid bleaching powder was early introduced as a means of destroying mustard gas in the field. (Fig. 9.)