6 



Black pigments rich in carbon of high specific gravity due to the presence of a large 

 percentage of ash are highly unsuitable for the manufacture of stamping inks. Only 

 the concentrated brands of coal-tar dyes should be used, unless the substances with 

 which the less concentrated are diluted have been found to actually contribute to 

 the working qualities of the ink to be produced. 



E. E. EWELL,O 

 Assistant Chief of Bureau. 



Revised by L. S. MUNSON, Chief, Contracts Laboratory. 

 Approved : 



JAMES WILSON, 



Secretary of Agriculture. 

 WASHINGTON, D. C., May 1, 1905. 



a Deceased. The original Circular No. 12 was prepared by Mr. Ewell when assist- 

 ant chief of Bureau, being dated January 29, 1903. 

 [Cir. 12] 



