148 PLANTS WITHOUT CHLOROPHYLL 



tiie food. Preservatives are of two kinds, those harmless to man 

 and those that are poisonous. Of the former, salt and sugar are 

 examples ; of the latter, formaldehyde and possibly benzoic acid. 



Sugar. — We have noted the use of sugar in canning. Small 

 amounts of sugar will be readily attacked by yeasts, molds, and 

 bacteria, but a 40 to 50 per cent solution will effectually keep out 

 bacteria. Preserves are fruits boiled in about their own weight of 

 sugar. Condensed milk is preserved by the sugar added to it ; so 

 are candied and, in part, dried fruits. 



Salt. — Salt has been used for centuries to keep foods. Meats 

 are smoked, dried, and salted ; some are put down in strong salt 

 sohitions. Fish, especially cod and herring, are dried and salted. 

 The keeping of butter is also due to the salt mixed with it. Vine- 

 gar is another preservative. It, like salt, changes the flavor of 

 materials kept in it and so cannot come into wide use. Spices 

 are also used as preservatives. 



Harmful Preservatives. — Certain chemicals and drugs, used as 

 preservatives, seem to be on the border line of harmfulness. 

 Such are benzoic acid, borax, or boracic acid. Such drugs may 

 be harmless in small quantities, but unfortunately in canned goods 

 we do not always know the amount used. The national govern- 

 ment in 1906 passed what is known as the Pure Food Law, which 

 makes it illegal to use any of these preservatives (excepting ben- 

 zoic acid in very small amounts). Food which contains this 

 preservative wdll be so labeled and should not be given to chil- 

 dren or people with weak digestion. Unfortunately people do 

 not always read the labels and thus the pure food law is ineffec- 

 tive in its working. Infrequently formaldehyde or other pre- 

 servatives are used in milk. Such treatment renders milk unfit 

 for ordinary use and is an illegal process. 



Disinfectants.^ — Frequently it becomes necessary to destroy 

 bacteria which cause diseases of various kinds. This process is 

 called dismfeding . The substances commonly used are carbolic 

 acid, formalin or formaldehyde, lysol, and bichloride of mercury, 



• Experiment to determine the most effective disinfectants. Use tubes of 

 bouillon containing different strength solutions of formaldehyde, lysol, iodine, car- 

 bolic acid, and bichloride of mercury. Results. Conclusions. 



