4-NITRO-5-METHYL-2-SULPHOBENZOIC ACID 
181 
low melting and high melting chlorides crystallized in a con- 
stant melting mixture which had a lower melting point than 
that of the low melting chloride. The two were separated in 
these cases by distilling in a vacuum. 
The formerly observed melting point for the high melting 
chloride is approximately correct, the new value adopted being 
134°, but now it has been definitely shown that the low melting 
point acid chloride melts at 83°, and is not involved as the 
prime cause of the oily mixture. In this case, as distinguished 
from the experience of others, no oil was produced when pure 
initial potassium salt was used, the two chlorides crystallizing 
out in absolutely distinct crystalline form. They were sep- 
arated by fractional crystallization, and the symmetrical, high 
melting chloride showed a tendency toward the formation of 
supersaturated solutions in carbon tetrachloride, the solvent used 
for the purification. The oily mass formerly found by Karslake 
and Borid was, however, reproduced by mixing with the low 
melting acid chloride, a portion of the acid chloride of the un- 
oxidized nitro-xylene sulphonic acid. Its source in that work 
was evidently the impurity mentioned at the beginning of this 
paper. 
. Symmetrical Acid Chloride. 
NOg • CHs • CgHg • SOgCl • COCl 
The symmetrical acid chloride was formed in the largest 
amounts when the potassium salt of the acid was treated with 
phosphorous pentachloride in an open dish at the temperature 
of the steam bath, the ratio of the symmetrical to the unsym- 
metrical acid chloride thus formed being about three to five, 
and the total yield reaching seventy-five per cent of the the- 
oretical. 
When the heating had caused) complete liquif action of the 
mass in the open dish, it was removed from the steam bath 
and poured into cold water. Phosphorous oxychloride and any 
phosphorous pentachloride remaining were dissolved in the water, 
and after a time the oil hardened. It was broken up with a 
stirring rod and ground with fresh water in a mortar. Finally 
the. powder was let stand in more water over night, filtered, 
and the solid dried over sulphuric acid in a dessicator. It was 
next dissolved in hot carbon tetrachloride, filtered, and let stand 
