APPENDIX 95 



solution of corresponding strength. Measure 25 c.c. of 

 the acid solution, add a few drops of phenolphthalein 

 solution (or cochineal solution if this is used in the 

 experiment for which the alkali is to be employed), and 

 run in the alkali till a pink colour (violet with cochineal) 

 is produced. Note the volume of alkali used. Repeat 

 this experiment two or three times, and from the 

 mean of the results calculate the ratio of the alkali solu- 

 tion to the acid solution. Thus, if 24.2, 24.15, and 



24.2 c.c. of soda were used for 25 c.c. acid the ratio is 



= 1.0^4 or i c.c. of soda = 1.034 c.c. acid. 

 24.17 



N N 



If the acid is strictly : the soda is : - X 1.034; 



2 2 



if the acid is, for instance, X i.oii, the soda is then 

 * X 1.034 X i.on = f X 1.0454- 



The soda may be diluted in the ratio of 1000 parts to 

 1045.4 parts, i.e. 45.40.0. of water are added to each 

 litre, but it is preferable to use the solution as it is, and 

 multiply the results by the factor. 



To standardise solutions( strontia) 5 c.c. of the 

 hydrochloric acid should be carefully measured, a 



2 



few drops of phenolphthalein solution added, and the 

 alkali run in till a faint pink colour is seen. Several 

 titrations should be made, and the mean taken. This 

 figure divided into 2.5 will give the strength of the 

 solution in terms of normal. Thus if 26.2, 26.3, and 

 26.25 c.c. were used in three experiments the mean is 



2 ^ 



26.25, and the strength is -- = 0.09505 N. 



