106 DRAININGS. 



into a saucer, pour over it half a teacupful of hot 

 water, and let it stand for a few hours in some warm 

 place. When it has acquired a dark blue color, pour 

 off into another saucer the infusion from the slimy 

 substance deposited at the bottom, and soak strips of 

 fine printing or letter paper in it, in order to stain 

 them blue. If the color of the paper when subse- 

 quently dried is still very faint, it must be soaked 

 again. The blue litmus-paper thus obtained is an 

 extremely delicate test of all fluids which are acid to 

 the taste. If a small teaspoonful of vinegar, or two 

 drops of sulphuric acid, are put into one or two 

 quarts of water, and the blue paper is dipped in the 

 mixture, it is almost instantly reddened. The chem- 

 ist calls such tests reagents^ and avails himself of 

 the blue litmus or test-paper as the most accurate 

 reagent for acids. Preserve these strips in a box, 

 because they are gradually deprived of their color by 

 the light. 



Let another portion of the blue paper strips be 

 passed through water weakly acidulated, and dried 

 when they have acquired a distinct red color. For 

 this purpose only from one to two drops of sulphuric 

 acid, or, what is still better, from six to eight drops 

 of lemon-juice, should be introduced into a pint of 

 water. The red test-paper is the most delicate 

 means of recognizing a class of substances opposed 

 to acids, that is, alkaline or basic bodies. If some 

 wood-ashes or burnt lime is scattered upon a strip 

 of red paper, previously moistened, or if a piece of 



