18 TESTING MISCELLANEOUS SUPPLIES. 



acteristic of rosin. The Hirschsohn test for rosin, which is less delicate than the 

 Ldebermann-Storch method, is as follows : 



Digest about 1 gram of the dried resin with approximately 20 cc of am- 

 monium hydroxid for twenty minutes, filter and acidify with acetic acid. With 

 pure damar the liquid remains clear, but if rosin is present a precipitate forms, 

 and when the proportion of rosin is large the entire acid liquid may become 

 gelatinous. The acid number of damar is lower than that of rosin and higher 

 than that of the hard varnish gums. An oil varnish made of hard gums will 

 generally have an acid number of less than 12. A damar varnish will have 

 an acid number between 15 and 20, a higher number generally indicating the 

 presence of rosin. 



OIL VARNISH. 



The methods of analysis for varnish are far from satisfactory. A number 

 of methods for determining the amount of gums in varnish have been proposed, 

 but none of them are reliable. This determination, therefore, is not made, but 

 the combined percentage of oil and gums is reported. 



1. Appearance and Odor. 



Transfer the sample if it is in a metal container to a glass-stoppered cylinder 

 or bottle and note its appearance, color, transparency, body, and whether any 

 sediment is deposited. The presence of light petroleum oil or wood turpentine 

 may often be detected by noting the odor of the sample. After making these 

 observations, the sample should be thoroughly mixed before making the re- 

 maining tests. 



2. Specific Gravity. 



Determine with a pyknometer, plummet, or hydrometer at 15.5 C. 



3. Flash Point. 



Determine as in spirits of turpentine; but begin testing at 25 C. and stir 

 the varnish while heating. A low flash point indicates light petroleum oil. 



4. Viscosity. 



The determination of viscosity is seldom necessary ; but if desired, make the 

 determination by the Engler-Ubbelohde method at 20 C. 



5. Volatile Oils. 



Weigh 100. grams of the varnish into a 500 cc flask, connect with a spray trap 

 ami a vertical condenser, and pass through it a current of steam, first heating 

 the flask in an oil bath at 100 C. ; with the steam still passing through, raise 

 the temperature of the bath to 130 C. Catch the distillate in a small separa- 

 tory funnel; continue distillation until 300 cc of water has been condensed. 

 Portions of this water may be drawn from the cock of the separatory funnel 

 from time to time, but care must be taken not to draw out any of the volatile 

 oil. Let the distillate stand until it separates into two layers, then draw off 

 the water and weigh the light oils in a tared stoppered flask. Filter the light 

 oils through dry p.-ipor and examine as directed under spirits of turpentine 

 (page 13). A slight error is caused by the solubility of turpentine in water; 

 i liis amounts to about 0.3 to 0.4 cc for each 100 cc of water. 



When sufficient varnish is available, it is well to take another portion and dis- 

 til, without steam or spray trap, placing the weighed flask in an oil bath. Note 



