DAMAR VARNISH. 17 



In calculating the percentage of rosin, assume the iodin number for pure 

 rosin to be 228, that for pure unbleached shellac to be 18, and for pure 

 bleached shellac, 10. These figures will tend to give somewhat low results on 

 rosin percentage, but should be used, as it is then safe to say that there is at 

 least as much rosin present as is found by analysis. 



3. Alcohol Insoluble. 



Add to 1 gram of shellac 60 cc of 95 per cent alcohol, heat to boiling, and 

 filter on a Gooch crucible ; wash with about 60 cc of boiling 95 per cent alcohol, 

 dry at 100 C. and weigh. 



4. Loss on Drying Water. 



Heat 1 gram for two hours in a water oven at 100 C. Loss in weight is cal- 

 culated as water. 



5. Ash. 



'Determine ash on 1 gram, heating only to dull redness. 



SHELLAC IN ALCOHOL. 

 1. Total Solids and Ash. 



Evaporate 1 gram of the varnish in a porcelain dish on the water bath and 

 dry to constant weight in steam oven (about five hours). Ash residue as in 

 dry shellac. 



2. Examination of Solvent. 



Note the odor of the varnish, as little can be learned from the odor of the 

 distillate. Distil 100 grams of the varnish until incipient decomposition begins ; 

 redistil the distillate, noting the boiling point, and determine the specific grav- 

 ity of the distillate. By this means it is usually an easy matter to determine 

 whether the varnish is made with wood alcohol, grain alcohol, or denatured 

 alcohol. Dilute a portion with three times its volume of water; if benzin is 

 present it will separate. 



3. Test for Rosin. 



Do not use the residue from the total solids determination, but carefully 

 weigh in a capsule a quantity of varnish sufficient to yield 0.2 gram of solid 

 material, evaporate to a paste, and treat the residue as described under "dry 

 shellac," paragraphs 1 and 2, page 16. 



DAMAR VARNISH. 



Damar varnish, which should be a solution of damar gum in spirits of tur- 

 pentine, is examined by the methods for oil varnishes (page 18). The percent- 

 age and nature of the volatile oil, specific gravity, and flash point are important 

 tests. It should yield little ash, which should contain no lead or manganese. 

 When flowed on glass it should set to touch in a very short time (less than 

 thirty minutes) and mixed with zinc white should yield a good white enamel 

 surface when applied to wood. 



In testing for rosin by the Liebermann-Storch test (page 19), the light claret 

 color characteristic of damar should not be mistaken for the violet color char' 



21694 Bull. 10912 3 



