GLYCERIN. 55 



at 30 C., strain through boiling Hoth into n somewhat larger flask, heat to 

 60 C., cool to 30 C., and determine the viscosity immediately by the Engler- 

 Ubbelohde method at 30 C. (The Hureau of Chemistry instrument requires 

 51.4 seconds to empty 200 cc water at 20.) Concordant results can not be ob- 

 tained by running the same solution a second time through the viscosi meter, 

 the solution flowing faster each time. Fairly good results, however, can be 

 obtained by heating the solution again to 60 C. and cooling to 30 C. When 

 the size of the sample will permit, make up enough solution to run duplicates. 



7. Jelly Strength. 



This is one of the most important tests. Fernbach states that no apparatus 

 gives as reliable results as the simple testing of the jelly by the finger. This, 

 however, is an unsatisfactory method when only occasional samples of glue 

 are examined. 



Weigh 50 grams of glue and 250 grams of water into a GOO cc beaker, allow 

 to stand at room temperature for thirty minutes, then heat in a water bath at 

 60 C. until dissolved, add 250 grams of water at 60 C., making a total of 

 500 grams of water. Mix the solution and pour 150 cc into a glass and cool 

 for one and one-half hours with cracked ice. While still in the ice determine 

 the strength by the shot test as formulated by Lipowitz and modified by 

 Fernbach. 



8. Melting- Point of Jelly. 



This determination is best made according to Cambon's fusiometer 6 method. 

 The apparatus used in the Bureau of Chemistry is only a very slight modifi- 

 cation of Cambon's, and consists of a metal cup (a ferrule) 22 mm high, 17 mm 

 in diameter at the top, and 15 mm in diameter at the bottom, weighing 7 grains, 

 and a glass tube 9 mm in diameter, and 160 mm long with the lower end 

 sealed. Weigh accurately 2 grams of glue, place in, a test tube with exactly 

 8 cc of water, cork, and allow to stand over night. Then dissolve the glue by 

 holding the tube in warm water, not over 60 C. By shaking the tube a homo- 

 geneous liquid is easily obtained. Place the metal cup on a horizontal sur- 

 face, suspend the glass tube vertically at about the center of the cup, with 

 the closed end approximately 1 mm above the botttom. Pour the glue solution 

 into the cup and allow it to set. (This may be hastened by surrounding the 

 cup with ice water.) Fill a 600 cc Jena beaker, 12 cm high and 9 cm in diam- 

 eter, two-thirds full of water at 15 C., and set it in a pan of water at 40 

 to 42 C. The water level in the pan should be about 15 mm below that in 

 the beaker. Clamp the glass tube in a vertical position at such a distance 

 above the center of the beaker that the metal cup is submerged to about ] mm 

 from the top. Suspend a centigrade thermometer, graduated in tenths, close 

 to the cup and note the temperature at which the cup drops. Good glues have 

 a melting point above 30 C., while that of inferior grades is several degrees 

 lower. 



GLYCERIN. 



As a rule, no determinations are necessary on glycerin except ash and specific 

 gravity. 



1. Ash. 



Ignite 10 grams at a low temperature, either in the muffle or in a hood having 

 a very good draft. 



a Fernbach, Glues and Gelatine, p. 46. 



&Ktittner and Ulrieh, Zts. off. Chem., 1907, 13: 121-126. 



