4-NITRO-5-METHYL-2-SULPHOBENZOIC ACID 
187 
acid, the imide separates almost quantitatively from the solu- 
tion. At slightly elevated temperatures it is more soluble so 
that it comes out in a nice crystalline condition. It is colorless, 
and the crystals as viewed under the microscope are platelike 
needles, so thin in one dimension that the edge appears only as 
a line under a magnification of 150 diameters. The insolubility 
of the precipitate makes it unnecessary to purify except by 
washing with water until free from chlorides. The imide is bit- 
ter tasting. It is readily soluble in alkali, as would be expected 
from the presence of the imide group. It forms salts with va- 
rious metals, by which it may be. characterized more completely. 
Its melting point is 213.5°. The methods of analysis were those 
used for the ammonium salt. 
.1168 g. imide required 9.00 cc .1084N HCl. 
.1156 g. imide required 8.97 cc .10'84N HCl. 
.1643 g. imide gave .1584 g. barium sulphate. 
Theory for CsHeOjNaS Pound 
Nitrogen, 11.57 per cent. 11.77 - 11.68 per cent. 
Sulphur, 13.22 per cent. 13.25 per cent. 
Silver Salt of the Imide. 
CO (1) 
NO. • CHs • C6H.<^ /N • Ag 
SO. (2) 
When the imide was dissolved in a large volume of hot water, 
and a solution of silver nitrate added, a white crystalline pre- 
cipitate slowly appeared. The crystals were platelike needles, 
somewhat rosetted, but these rosettes were very loosely held to- 
gether and easily broke up into the long, thin, square ended 
needles. The salt contained no water of crystallization. It was 
less soluble than the silver salt of the cyan acid to be described 
later. The determination of silver was made by charring the 
salt in a porcelain crucible with sulphurc acid, and reducing 
the silver sulphate directly in the same container. This seemed 
to give better results than attempting to precipitate the silver 
as the chloride from a litre or more of solution. Some difficulty 
was encountered in the heating, however, as the silver salt de- 
composed suddenly and the loss by the puffing from the crucible 
spoiled the analysis, unless the rate of charring was carefully 
regulated. 
