CHEMICAL EXAMINATION OF RAW MATERIALS. 207 



two drops of litmus tincture and diluted with four to six times 

 its quantity of distilled water. The beaker is placed upon a 

 Avhite support under the burette and the soda solution in the 

 latter ejected in a strong jet by pressing with the right hand the 

 handle-joint of the clip, the fluid being constantly agitated by 

 gently swinging the beaker with the left. The influx of soda 

 solution is interrupted as soon as a blue coloration on the point 

 where it runs in is observed. After thoroughly stirring the fluid 

 with a glass rod, the soda solution is again allowed to run in, but 

 now drop by drop, the fluid being stirred after the addition of 

 each drop. This is continued until the fluid has acquired a violet 

 color with a strong reddish shade, and the addition of one drop 

 more of soda solution changes the color to blue. The appearance 

 of the violet coloration is called the neutralizing point, while the 

 change of color from violet to blue indicates that the fluid is now 

 neutral, i. e., contains neither free acetic acid nor an excess of 

 caustic soda. The determination is based upon the coloring sub- 

 stance of litmus appearing red in acid, violet in neutral, and blue 

 in alkaline solutions. 



Instead of soda test liquor a solution of ammonia is sometimes 

 used to saturate the acid. The solution is prepared by adding 

 water to concentrated ammonia till the specific gravity is 0.992 ; 

 1000 grains of this dilute ammonia contain one equivalent of am- 

 monia, which is capable of saturating one equivalent of acetic 

 acid. The application of this test is similar to that already de- 

 scribed. 



There is some difficulty in preserving the dilute ammonia of 

 the same strength, which is an objection to its use ; but a uni- 

 formity of concentration may be insured by introducing into the 

 bottle two glass hydrometer bulbs so adjusted that one remains 

 barely touching at the bottom, and the other floats just under the 

 surface of the liquid as long as the test liquor retains the proper 

 strength. If a part of the ammonia volatilizes, the specific 

 gravity of the liquor will become proportionally greater, and the 

 glass bulbs rise ; the lower one higher from the bottom, and the 

 upper one partly above the surface. When this happens, more 

 strong ammonia is added, till the hydrostatic drops are properly 

 readjusted. 



