270 § 140. WOOL. 



h. Water. — Dry 3-4 grms. at 100° C, and weigh it. 



c. Wash a quantity of the wool in a manner similar 

 to that practiced in the factory. For this purpose pre- 

 l^are a solution of 3 parts of hard soap and 2 of crys- 

 tallized sodic carbonate, in 100 of distilled or rain-water, 

 heat 20 parts of this solution to 50-55°, put 1 part of 

 wool in it, and stir the mixture gently for 15 or 20 

 minutes, while the solution is maintained at the same 

 temperature ; then take the wool out, wash it in severaj 

 portions of water, dry it in the air, spread it out on fine 

 wire gauze, tap the gauze gently underneath several times, 

 pick off adhering particles of foreign matters with the 

 pincettes, dry the residue at 100° C, and w^eigh it. If, 

 after this treatment, the w^ool still feels greasy, it should 

 be washed again in a somewhat stronger bath. Finally 

 extract any remaining fat with carbonic disulphide or 

 ether, dry the residue again at 100°, and weigh it. 



d. Treat another portion of the wool in the reverse 

 manner, that is, first with ether (§ 87), and then, after 

 drying and weighing the residue, wash it in the bath of 

 soap and soda. Determine the fat in the etherial solu- 

 tion, or an aliquot part of it. 



e. Determine the ash in the residue of c and d in the 

 usual manner (§ 127). Examine this ash for sand by 

 digestion with hydrochloric acid, and boiling with sodic 

 carbonate (§ 58). 



f. To determine the specific gravity of the j^ure wool 

 obtained in c and d^ weigh it first in air and then in car- 

 bonic disulphide of known specific gravity (§ 35, J, d). 



TANNER'S BARK. 



140. a. Preparation of the sample.— Cut the bark to 

 be examined, lengthwise, in very thin shavings. 

 h. Water.— Desiccate 1-2 grms. at 100° C. 

 c. Tannic acid. — Pour 100 c.c. of water over the dried 



