46 TESTING MISCELLANEOUS SUPPLIES. 



as the base of the ink. This may or may not be an undesirable result. If the 

 colorless band is due to a difference in the rate of penetration, it is undesirable. 

 If it shows that the dye contained in the ink has an affinity for the fibers of 

 the paper, it is evidence of a valuable quality. 



Additional information can be obtained from the penetration test by removing 

 the strips of paper from the vials, cutting off the part of the paper which has 

 actually been immersed in the ink, and treating the upper part successively 

 with petroleum, ether, alcohol, and other solvents for removal of the constitu- 

 ents of the ink soluble in these liquids. The extent to which the dye or dyes 

 contained in the ink resist the action of 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 informa- 

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

 the fiber 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. 



To make the determination allow the strips to remain in position until the 

 next day, remove, dry between blotters, and examine for a rise of dye or carbon. 

 If either dye or carbon rises as far, or nearly as far, as the base of th ink the 

 rise is pronounced " satisfactory." Less than this is not acceptable except in 

 the case of glycerin inks, which rarely give any rise of carbon. A small 

 amount of rise in the latter inks must be accepted as satisfactory. To deter- 

 mine whether the rise is carbon or simply dye, pick off particles of the paper 

 and adhering ink at intervals on the strip and mount on slides with water or 

 alcohol. Examine with the microscope, using low power; note size of the car- 

 bon grains. The grains adhere to the outside of the paper fibers in clots, as a 

 rule, but it is often difficult to distinguish them. 



4. Sedimentation Test, 

 (a) APPARATUS. 



(1) Glass-stoppered cylinders, graduated for 200 cc and fractions thereof, 

 the distance between the bottom and the 200 cc mark being 25 cm (10 inches). 

 If unobtainable, other cylinders may be. substituted, marks being placed at 

 distances 25 cm (10 inches) and 16 mm (} inch) from the bottom. 



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



(3) A millimeter rule. 



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

 having a capacity of from 10 to 15 cc. 



(b) 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. The ink 

 should be previously tested to determine a proper solvent for both base and 

 dye. Alcohol is generally the solvent to use for rosin inks. It may be neces- 

 sary to use other solvents, such as gasoline (boiling point 50 to 60 C.), ether, 

 brnxol, etc. Dissolve the ink in the cylinder in the appropriate solvent and 

 dilute up to the 200 cc mark, stopper, and shake thoroughly. Allow the cylin- 

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

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



