294 HORTICULTURE FOR SCHOOLS 



of the fruit, and it prevents the growth of bacteria and fungi. 

 Fruit is not dried so completely as to remove all the moisture ; 

 nor can it always be kept in perfectly air-tight containers; 

 it is, therefore, always slightly moist, thus making possible 

 the development of decay-producing organisms. Sulfur, how- 

 ever, prevents the growth of such structures, and is used 

 wherever fruit is preserved by drying. 



409. The chemistry of sulfuring. When sulfur burns in 

 air, it unites with oxygen, forming a new substance known as 

 sulfur dioxide. This has the peculiarly pungent odor so 

 characteristic of burning sulfur. Sulfur dioxide gradually 

 comes in contact with the moisture of the fruit, forming 

 sulfurous acid, which, on being exposed to the air, unites 

 with oxygen forming sulfuric acid. All sulfured dried fruit, 

 therefore, contains a certain amount of sulfuric acid and a 

 lesser amount of sulfurous acid. When the pure food and 

 drug act was passed in 1906, the chemists in charge of its 

 enforcement feared that these acids in the fruit rendered it 

 injurious to the consumer. Fruit-growers immediately real- 

 ized that, if sulfuring were not allowed, their industry would 

 be destroyed ; for sulfuring not only improved the appearance 

 of the fruit, giving it an amber-like color when dried, but also 

 prevented the growth of bacteria and fungi and kept away 

 injurious insects, which would otherwise destroy large quan- 

 tities. The matter was submitted to a board of experts and 

 after careful investigation it was found that the acids present 

 in moderate quantities were not injurious. The Government 

 has, therefore, permitted the treatment of all dried fruits 

 with moderate quantities of sulfur dioxide gas. 



410. Drying of other fruits. The drying of prunes and 

 raisins differs from that of other fruits, as they contain 

 sufficient sugar to permit of being dried without the removal 

 of the pit or seeds. In the case of prunes, it is necessary first 

 to crack the skins so that the water can escape rapidly. This 

 is done by dipping the prunes for a few minutes in a solution 



