48 § 45. BASES AND ACIDS WITH IIEAGENTS. 



quired to combine with it and form a salt which is neutral 

 to test-papers (§ 45). 



PREPARATION OF THE STANDARD ACID AND ALKALINE 

 SOLUTIONS. 



45. a. — Sulphuric acid. — To about 1100 c.c. of water 

 add nearly 68 grms. of concentrated sulphuric acid, mix 

 the whole well together, let the mixture cool to the tem- 

 perature of the working room, and then estimate sulphu- 

 ric acid with baric chloride (§ 59) in two or three portions 

 of 20 c.c. each, with the utmost care ; having in this way- 

 determined the strength of the solution, dilute it set that 

 one litre shall contain exactly one equivalent of the acid 

 expressed in grammes, or 40 grms. Supposing that the 

 mean of three satisfactory determinations, as above, gives 

 0.84 grm. of sulphuric acid in 20 c.c. : then we learn from 

 the proportions, 20 : 0.84 = 1000 : 42, and 40 : 42 = 

 1000 : 1050, that 50 c.c. of water must be added to one 

 litre of the acid that we have made, in order that it shall 

 be of tlie proper strength ; to cifect this further dilution, 

 measure out 1000 c.c. of tlie acid in the litre flask, pour 

 it without any loss into tlie bottle in which it is to be 

 kept, rinse the walls of the flask with exactly 50 c.c. of 

 distilled Avater, pour this water likewise into the same 

 bottle without loss, and mix the acid and rinsings togetlier 

 well; finally pour about half the contents of the bottle 

 into the flask, rinse oft' the walls of the flask with the 

 liquid, and pour it back into the bottle. 



The bottle containing this standard acid should be kept 

 well stoppered ; each time that a portion is to be taken 

 out, the contents of the bottle should be shaken up in 

 such a manner as to rinse down the water that may have 

 evaporated in the space above the liquid and condensed on 

 the glass. {Fresenius. Quantitative Chemische Analyse.) 



Since 40 is the equivalent of sulphuric anhydride, SOg, 



