42 Estimations occurring in Agricultural Analysis [63, 64 

 If, therefore, we wish to have our acid seminormal, we 



must dilute every ^ c.c. until it becomes io c.c. : or, 

 x 



multiplying these quantities by ioo, we must dilute 2 ^ c c. 



x 



to a litre. 



To do this pour the calculated quantity of the dilute acid 



[-45 c.c.) into a stoppered, graduated litre cylinder, and 



fill up to the litre mark with distilled water. Mix well by 

 shaking. The solution so prepared should be accurately 

 seminormal. 



Keep this standard solution in a well-stoppered Winchester 

 quart bottle, taking care that it is quite clean and dry before 

 pouring in the liquid. If it be not quite dry, wash it out with 

 a little of the standard acid ; throw away the washings, then 

 pour in the rest of the acid. 



PREPARATION OF SEMINORMAL CAUSTIC 

 POTASH SOLUTION 



63. Weigh out on a rough balance 10 grams of solid caustic 

 potash j place this in a 20-oz. beaker, together with about 

 300 c.c. of distilled water, and allow it to dissolve. When all 

 the solid has disappeared, pour the liquid into a clean litre flask 

 and make up to the litre mark with distilled water. Caustic 

 potash gives out considerable heat on dissolving, so that the 

 solution will be distinctly warm. Before proceeding farther it 

 must be cooled (fig. 24). After cooling, the solution will be 

 found to have shrunk slightly. Make up again to the litre 

 mark, and mix thoroughly. 



64. Standardisation. — Fill a burette with seminormal 



student when calculating the results of the more complex analyses de- 

 scribed later on. 



