(The time indicated is the interval between the pouring of the pectin solution into the sugar sirup and the pouring of the mixture into glasses. Jellies contain 60 per cent of sugar, 2.5 grams of apple pectin 119°F., phosphoric acid as indicated. Temperature of pectin solution 36°C; of sugar solution 65°C; of final mixture 55°C.) (Olsen)

25% phos-phoric acid solution cc.

Series B 90 seconds

Series C 50 seconds

Series D 8 seconds

Jelly strength

pH

Jelly strength

pH

Jelly strength

pH

0.26

. . .

. . . .

0.0

3.27

. . . .

. . .. .

0.36

33.0

3.10

. . .

36.5

3.13

0.56

69.0

2.80

. . .

67.0

2.88

0.86

. . .

80.0

2.50

. . . .

. . . .

0.96

41.0

2.39

....

115.0

2.40

1.06

. . .

....

75.0

2.37

....

....

1.26

....

....

61.5

2.24

. . . .

. . .

1.56

19.0

2.13

....

....

120.0

2.13

1.96

14.5

2.03

28.5

2.00

145.0

2.01

3.96

....

....

....

....

135.0

1.76

Goldthwaite has reported that, when tartaric and citric acids were used to acidify fruit juices deficient in acid, tartaric acid gave better results, the texture and flavor being better than when citric acid was used. Tarr's results confirm Goldthwaite's observations. Spencer explains this difference in the following manner. Since pectin sols are partially stabilized by a negative charge, the preferential absorption of one anion above that of another would increase the stability of the pectin sol. In other words, the citrate ion is more strongly absorbed than the tartrate ion, hence increases the negative charge on the pectin to a greater extent, making it more stable, less easily precipitated, so that a weaker jelly is obtained with citric acid than tartaric, if the same concentrations of pectin and sugar are used.

Methods of reporting acidity of fruit juices. Investigators have reported concentration of acids required for jelly in different ways. The pH gives the concentration of hydrogen ion or ionized part of the acid. Some report acid as number of cubic centimeters per 100 grams of jelly. However, work done some time ago was usually reported in percentage of some acid, not necessarily the one found in the fruit. It has often been reported as sulfuric acid. The concentration of the acid is determined by titration with an alkali; from the quantity of alkali required the percentage of acid is calculated. Campbell states that 0.3 per cent as sulfuric acid is required to produce a jelly of good quality, the minimum being 0.27 and the maximum 0.5 per cent. Goldthwaite has reported from 0.154 to 1.892 per cent as sulfuric acid. Singh has reported still lower percentages of acids than these, but his jellies with a very low percentage of acid contain an unusually high percentage of pectin.