The demand for sulfur black with a red shade has far Surpassed that for the blue tinted ones. The current opinion seems to recognize that pieric acid is a necessary ingredient in producing the red tint. On aocount of the present shortage of picric acid

which is also an expensive chemical and dangerous to handle

its omission from the manufacturing procedure would solve an acute problem of the sulfur black dye industry. In this investigation

the authors at- tempted and succeeded in obtaining the red shade without using picric acid by a mere variation Of the proportion of the three components

namely dinitro-chl-orobenzene

sodium sulfide and sulfur. The experiment was carried out with similar equipment used by factories of the local district except on a miniature scale. In some factory practice

the preliminary hydrolysis of the dinitro-chlorobenzene is performed in an iron reactor containing all the caustie soda solution with the dinitro-chlorobenzene added subsequently in one portion. When so operated

there is a period of vigorous chemical reaction

which renders temperature control very difficult. To avoid this

the caustic soda soiution was added dropwise to the warm din-itro-chlorobenzene suspension instead

which procedure has already been adopted by some local factories. This is a point worth mentioning

as the authors be-lieve that any careless operation would eventually affect the quality of the dye produced. Two series of experiments were performed. In the first series

the poly-sulfide index was fixed while changing the mole ratio of dinitro-chlorobenzene to sodium polysulfide

and in the other the polysulfide index was varied. The following conclusions were obtained: (1) Fixing the polysulfide index at 3.6 but varying the mole ratio of D.N.C.B. to polysulfide

the effective range of color formation is found to be between l:1.59 and 1:1.72. If the ratio is less than 1:1.59

it fails to give a dye; while on the other hand

when the ratio exceeds 1:1.72

the color intensity may be decreased. Within this range

increasing the ratio increases the rate of thionation without any apparent affect on the color intensity. However

the shade is substantially modified. The red shade is produced only when the ratio is kept ithin an even narrower range of 1:1.63 to 1:1.64. This rather indicates that the control of composition is exceedingly important and should be strictly adhered to. (2) With a fixed ratio of D.N.C.B. to polysulfide at 1:1.58

which showed no tendency of dye-formation at a polysulfide index of 3.6

the index was in- creased up to 3.9. (The highest polysulfide index used in the sulfur black in-dustry is usually 4.0). In all these cases

dyes were obtained with a higher in-tensity accompanying a larger index. The shades

however

are all greenish. When the fixed ratio was increased to 1:1.62 and the polysulfide index gradually lowered from 3.9

the color intensity of each dye produced was less than that of the corresponding one with a smaller D.N.C.B. to polysulfide ratio

although the shade was also an invariable green one. The lower limit

where the dye-forming ability of the composition disappears

is found to be at a polysulfide index of 3.1. It is thus believed that with 3.9 as the upper limit of the poly-sulfide index

the lower limit would progressively shift upward by decreasing the D.N.C.B. to polysulfide ratio

until a point is ultimately reached where the two limits would coincide. This would give a dye of maximum intensity. Further research is required to verify this fact. (3) It is also logical to conclude from the results of this experiment that the intensity and the red shade of sulfur black are antagonistic. It thus neces-sitates a certain degree of compromise in actual factory practice.