54 TESTING MISCELLANEOUS SUPPLIES. 



GLUE. 



Chemical analysis gives little information in regard to the value of glue. 

 The chemical determinations are of more use in deciding as to whether a 

 delivery is the same as a sample submitted than in deciding which is the best 

 of a series of samples. Fernbach says, " save for alkalinity or acidity, the 

 chemical properties of glue are not factors in rational systems of test." In 

 determining whether specifications have been complied with in making inking 

 pads chemical tests are often of use. 



1. Moisture. 



Heat 3 grams of the finely divided sample for two hours in an oven at 105 

 to 110 C. It is important to use about the same quantity each time. Fernbach 

 states that a good glue should contain not less than 8 nor more than 16 per 

 cent of moisture. 



2. Ash. 



The sample used for the moisture determination may be ashed. Ignite in 

 porcelain or quartz, do not use platinum. Care is necessary in the ignition, 

 which should be carried out at as low a temperature as possible. The ash 

 should vary from 1.5 to 3 per cent. The condition of the ash gives some clue 

 as to the origin of the glue. If the ash fuses, gives a neutral reaction, and con- 

 tains traces of phosphates and chlorin, it indicates a bone glue. The ash of a 

 hide glue does not fuse, is slightly alkaline, and does not contain chlorids and 

 phosphates. 6 



3. Reaction. 



Test the solution in water with litmus paper. A quantitative determination 

 is seldom of use. 



4. Gelatin. 



A satisfactory approximation of the gelatin content is obtained by deter- 

 mining the nitrogen and multiplying by 5.56. 



5. Water Absorption. 



Place 10 grams of the sample, preferably in sheet form, in a weighed 400 cc 

 beaker, pour 200 cc of water at 15 C. on the glue, cover the beaker, and let 

 it stand for twenty-four hours in a refrigerator at a temperature from 

 14 to 18 C. Then pour off the water and weigh the remainder. With ground 

 Klue s<im> difficulty may be experienced in decanting the water; this is some- 

 times ;i voided by using a cage of fine wire gauze or a piece of bolting cloth 

 to hold the ground glue. The temperature at which the water absorption 

 is determined may be varied, but the figures obtained at one temperature MIV 

 not- to |M ennipiircMl with those at another. The determination can not be 

 riirric<l out on most glues nt tempenitnivs much above 20 C. 



6. Viscosity. 



Soak 50 grama of glue in 250 cc of water (at 20 C.) over night. Then dis- 

 solve by \v:i nniiig. not over <K) C., transfer to a 500 cc flask, dilute to the in;irk 



"<;iues and Gelatine, p. 4. 

 6 Ibid., pp. 59-61. 

 Ibid., pp. 61-63. 



