274 HORTICULTURE FOR SCHOOLS 



EXERCISE IV. Eight-to-one test for ripeness of oranges. 



Materials. Brix spindle graduated in tenths, beaker, centigrade 

 thermometer, glass cylinder to hold Brix spindle, 10 or 25 c.c. pipette, 

 one burette and support; one liter standard alkali solution, 1 ounce 

 indicator solution, lemon squeezer, large glass or granite cup, straining 

 cloth or wire strainer. 



Procedure. Take a sample of nine to twelve oranges, cutting them 

 in half. Extract juice with lemon squeezer and strain. Introduce 

 juice into glass cylinder until there is sufficient to fill the cylinder. 

 Take spindle reading (being careful to write this down) together with 

 temperature. From the table obtain temperature correction and add 

 or subtract to Brix reading as case may be. This corrected reading 

 indicates the percentage of soluble solids present in the orange juice. 



Next dbcermine acid present as follows: Draw off 10 or 25 c.c. of 

 juice into a clean glass beaker. Add some distilled water and several 

 drops of indicator. Pour standard alkali solution 1 into the burette 

 until the upper end of the alkali column is on the zero mark. Now add 

 alkali solution to the orange juice, at first gradually and finally, drop 

 by drop, until a permanent pink color appears. Note the reading of 

 the burette. Multiply this reading by ten and you have the milligrams 

 of acid present in the sample of juice. Next, change cubic centimeters 

 of juice to milligrams of juice by multiplying by 1000 and the specific 

 gravity. This can be found by following the directions under Table II. 

 To obtain the percentage of acid present, multiply milligrams of acid 

 by 100, then divide by milligrams of juice. Now divide the percentage 

 of soluble solids by the percentage of acid and the answer is the ratio. 



E. g. Suppose that the Brix reading is 12.6, temperature 13 "C," 

 cubic centimeters of juice 25, and of standard base necessary to 

 neutralize the juice, 36. The problem is worked as follows: 



Correction for 13 is .2. This is to be subtracted. 12.6 minus .2 

 equals 12.4. This answer represents the percentage of soluble solids 

 in the orange juice. The specific gravity of the solution with a test 

 of 12.4 is 1.05021. The weight of 25 c.c. of juice is found by multiplying 

 this figure by the specific gravity: 25X1.05021 equals 26.25525 grams. 

 Change to milligrams by multiplying by 1000; this equals 26,255.25. 

 Multiply 36X10 and X100 equals 36,000. Divide this by 26,255.25 

 equals 1.37+- This is the percentage of acid in the juice. Divide the 

 percentage of soluble solids (12.4) by the percentage of acid (1.37); 

 this equals 9.05 and the ratio is 9.05 to 1. 



To prepare standard solution, dissolve 6.25 gm. sodium hydroxide 

 in enough distilled water to make a liter of solution. 



