12 BULLETIN 540, U. S. DEPARTMENT OF AGRICULTURE. 
which the amount of pectin is small or in the case of a fruit in which 
large amounts of water are necessary for the extraction. It should be 
cooked until it jells. This pomt has been reached when a ther- 
mometer inserted in the solution indicates a boiling point of 103° C. 
(217° F.). Ina few cases it is necessary to cook the juice to a higher 
temperature, 105° C. (218° F.). 
References.—Univ. Ill. Bul., 8 (1911), No. 7, Goldthwaite; Preser- 
vation of Food in the Home, Univ. Mo. Bul., 15 (1914), No. 7, pp. 
23-29. 
Correlation.—Physics: The effect of substances in solution upon 
the boiling point of that solution. Arithmetic: Explain the different 
thermometers, Fahrenheit. and Centigrade, and compute changes of 
readings from one to the other. 
LESSON 10. 
Problem.—Examination of the jellies made last time, an analysis 
of the process, and a discussion of the reasons for any variations in 
the results. 
Points to be brought out.—Failure may be due to (1) absence of 
pectin in the juice. This can be determined by the alcohol test. 
(Ref. Univ. Mo. Bul., 15 (1914), No. 7, Preservation of Food in the 
Home, p. 23); (2) a deficiency of acid which prevents a perfect jelly 
from forming. Sugar sometimes crystallizes out from a jelly made 
from juice containing a small proportion of acid. If cooked too long, 
a candy rather than a jelly will result. 
References.—U. 8S. Dept. Agr., Farmers’ Buls. 78*, 122*, 175*. 
Correlation.—Chemistry: Result obtained by boiling cane sugar in 
an acid solution, and the effect of this in retarding crystallization. 
LESSON 11. 
Problem.—To study the water supply from the standpoint of its 
use for laundry purposes. Wash the laboratory aprons and towels 
in water from different sources and compare the ease of the process, 
the amount of soap required, and the appearance of the article after 
laundering. In case the water is very hard, test the effectiveness of 
various alkalis in softening it. Show how to detect an alkali. 
Points to be brought out.—Hardness of water is due to the mineral 
matter in solution. Some of this is thrown out of solution when the 
water is boiled. Hardness of water which may be corrected by boil- 
ing is termed temporary hardness. That which is not remedied by 
boiling is called permanent hardness. Soap does not dissolve readily 
in hard water because it forms an insoluble compound with the 
mineral matter present. The scum which forms on the top of hard 
water when we use soap with it is an example of such an insoluble 
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