50 § 45. BASES AND ACIDS WITH REAGEJ^TS. 



of the alkali, expressed in milligrammes or fractions of a 

 gramme as above. 



h. Standard oxalic acid. — Put G3 grms. of pure crys- 

 tallized oxalic acid in a litre flask, fill the flask up to 

 about two-thirds with water, and, after the acid is entirely 

 dissolved, add more water until it rises nearly to the mark 

 on the neck of the flask ; bring the water to a tempera- 

 ture of 15° C, and then, holding the flask by the rim, so 

 that it will take a vertical position, carefully add water 

 up to the mark on the neck. Mix the whole well together 

 by shaking, transfer the liquid to a well stoppered bottl'e, 

 and keep it in a dark place. As 63 is the equivalent of 

 crystallized oxalic acid, expressed in grammes, this nor- 

 mal solution contains, like the standard sulphuric acid, 

 one equivalent of the acid expressed in milligrammes, 

 =63 mgr. or 0.063 grm., in one cubic centimetre. 



c. A standard soda solution is often wanted in connec- 

 tion with the use of the standard acid, and for other pur- 

 poses, and its preparation may be described here. 



It is made of such a strength that one cubic centimetre 

 of it will be exactly neutralized by one cubic centimetre 

 of the standard acid, or will contain 0.031 grm. of sodic 

 oxide, Na^O. 



To prepare it, put 5 c.c. of the standard acid in a small 

 flask with a very little cochineal solution, and then add a 

 diluted solution of sodic hydrate, of which a considerable 

 quantity has been previously made, from a 5 c.c. pipette 

 graduated into twentieths of a cubic centimetre, very 

 slowly and with constant shaking of the flask, until the 

 reddish-yellow color is just changed to purple ; suppose 

 that 2 c.c. have to be added ; then evidently 3 c.c. of w^a- 

 ter must be added to 2 c.c. of the soda solution, in order 

 to make 5 c.c. of the latter that shall exactly neutralize 

 5 c.c. of the standard acid ; or ^^'""° = the amount of 

 water to be added to one litre of the sodic solution, to 



