these solvents and the extent to which the lampblack has passed up the strip of blotting 

 paper are indices of the quality of the ink. 



An examination of the strips with the microscope will give valuable information 

 regarding the rise of carbon in the paper and the affinity of the dye for the fibers of the 

 paper. With many inks the carbon will not rise above the surface of the liquid, while 

 with others it penetrates the paper to the same height as the dye. With this class of 

 inks it is important that the base of the ink have the power to carry the carbon well into 

 the fibers of the paper. 



4. SEDIMENTATION TEST. 



(1) Apparatus. 



(a) Glass-stoppered cylinders, graduated for 200 cc and fractions thereof, the distance 

 I between the bottom and the 200 cc mark being 25 cm (10 inches). Failing these, other 

 cylinders may be substituted, marks being placed at distances 25 cm (10 inches) and 

 16 mm (|| inches) from the bottom. 

 (6) A pair of dividers with arms 15 cm long or longer. 



(c) A millimeter rule. 



(d) Pipettes made from straight tubing (7 mm), at least 30 cm in length and having a 

 capacity of from 10 to 15 cc. 



(2) Determination. 



By means of the special pipette introduce carefully, drop by drop, into one of the 

 200-cc cylinders, exactly 16 mm depth of the ink to be tested. To this add petroleum 

 ' ether (boiling point 50-60), ordinary ether, alcohol, benzol, anilin, or other solvent 

 which has been found by previous tests to be suitable for the base of the ink as well as 

 for the dye, until the 200-cc mark is reached; stopper, and shake, thoroughly. Allow 

 i the cylinder to stand, and record from time to time, by using the dividers and milli- 

 I meter rule, the height of the top of the layer of sediment which collects in the bottom 

 ' of the cylinder, expressing results in millimeters. During the first hour observations 

 should be made at intervals of 15 minutes; later, each hour for several hours succes- 

 sively, and then twice daily for a week to ten days. 



After the settling of the top of the layer of sediment has entirely ceased, the height of 

 i the sediment should equal or exceed 16 mm, the amount of ink taken for the test. The 

 | rate of sedimentation is an index of the state of division of the carbon, some inks show- 

 i ing no appreciable layer at the expiration of a ten-day test. 



In the case of some inks the supernatant liquid above the sediment is of such a dark 

 , color that there is difficulty in locating the top of the sediment, even when the cylinder 

 i is inspected by light reflected at various angles. In this event, the use of a dark room 

 1 with a light placed so as to give a strong ray through a small aperture will locate the top 

 i of the layer of sediment in all cases except when the ink contains a very large percen- 

 ; tage of a dense dye. 



5. DETERMINATION OF LAMPBLACK. 



Load a porcelain gooch with asbestos, using a felt about one-fourth of an inch thick. 

 After washing the felt thoroughly with water to remove fine particles, finally wash with 

 alcohol and ether, dry, and weigh. Weigh out about 5 grams of ink in a small beak'er, 

 dilute with a suitable solvent (alcohol is used in case of rosin-oil inks), transfer to a 

 gooch crucible, and wash until all oil and soluble color is removed. Finally, wash 

 with alcohol and ether, dry, and weigh. 



6. DETERMINATION or ASH. 



The lampblacks prepared for the manufacture of canceling ink yield less than 0.5 of 1 

 per cent of ash when burned, and the coal-tar dyes employed should contain no mineral 

 matter other than that which is an essential part of the molecules of the substances to 

 which the tinctorial power of these dyes is due. 



[Cir. 12] 



