61, 62] Seminormal Sulphuric Acid 41 



pour the liquid into a large bottle, and force a rapid stream of air through 

 it. This may be done by means of the blowpipe bellows. 



61. Standardising. — Carefully clean a burette, washing it 

 first with distilled water, then with a portion of the acid which 

 has just been made up. Allow it to drain for a minute, then 

 fill it with the acid. Drop an Erdmann's float into the top of 

 the burette, and allow the liquid to run from the tap, or pinch- 

 cock, until the mark on the float stands at the o c.c. mark on 

 the burette. Now allow exactly 10 c.c. to run out into a clean 

 12-oz. beaker; dilute to about 50 c.c, and determine the 

 amount of H 2 S0 4 exactly as described in paragraphs 28 to 30. 

 As soon as this is started, take another 10 c.c. from the burette, 

 and make a duplicate determination in the same way. Should 

 the two determinations agree pretty closely, then their mean 

 may be taken as the true quantity of H 2 S0 4 contained in 10 c.c. 

 of the solution. The next thing is to calculate, from this result, 

 how much water must be added to make the solution exactly 

 seminormal. 



62. A normal solution (see paragraph 58) contains 49 grams 

 of pure H 2 S0 4 * per litre. Therefore a seminormal solution 



such as is being prepared, should contain --2 = 24-5 grams 



per litre, or -245 gram per 10 c.c. 



Now, by experiment we have found how much H 2 S0 4 

 10 c.c. of our solution contains. Call this x. 



If x grams of H 2 S0 4 are contained in 10 c.c, 

 then 1 gram ,, is ,, 



.-. -245 gram ,, is ,, 



1 On page 23 a method was described for the estimation of sulphuric 

 acid, where the result was calculated as SO a . The use of the formula 

 H 2 S0 4 in volumetric and of the anhydride S0 3 in gravimetric analysis is 

 merely a matter of convenience which will be better understood by the 



