§ 45. PEEPAEATIOX OF THE STANDARD SOLUTIONS. 49 



and this standard or normal solution contains an equiva- 

 lent of the anhydride expressed in grammes, in a litre, 

 ( = 1000 cubic centimetres) it contains, then, an equivalent, 

 expressed in milligrammes, in one cubic centimetre = 40 

 mgr. or 0.04 grm. The quantity of acid in one cubic centi- 

 metre will combine with exactly one equivalent of potassic 

 oxide or potassa, K^O, expressed in milligrammes, = 47.1 

 mgr. or 0.0471 grm., and form a salt whose solution is 

 neutral to test-2:)apers ; in a like manner, the acid in one 

 cubic centimetre of the standard solution will combine 

 with or neutralize one equivalent of sodic oxide or soda, 

 Na^O, expressed in milligrammes = 31 mgr. or 0.031 grm., 

 or with one equivalent of ammonic oxide, (NHJ^O, = 26 

 mo;r. or 0.026 grm. 



The neutrality of the solution may be determined by 

 its effect on paper that has been colored by litmus, or by 

 adding a small quantity of a solution of litmus, or of 

 cochineal or curcuma root. Litmus is colored blue by 

 free alkali, and red by free acid ; cochineal under the same 

 circumstances is colored purple and light reddish-yellow, 

 while curcuma or turmeric is colored brown by free alkali, 

 and yellow by acids. 



If, then, to a solution containing any one of the alkalies 

 just mentioned, either in a free state or combined with 

 the weak carbonic acid, we add a little cochineal solution, 

 and then the standard acid from a burette or a graduated 

 l^ipette, with constant stirring, until the i^urple color sud- 

 denly disappears, and a reddish-yellow one takes its place, 

 that remains permanent throughout the whole liquid, we 

 may know that, for each cubic centimetre of acid added, 

 there were 0.0471 grm. of K,0, or 0.031 of Xa^O, or 0.026 

 of (NHJ^O in the solution; the whole amount of the al- 

 kali in the quantity of its solution taken for analysis will 

 be given by the product of the number of cubic centime- 

 tres of acid required, into the corresponding equivalent 

 3 



