THE PRESERVATION OF FOOD BY CHEMICALS. 405 



and hung in wood smoke for several days. They are then stored in a cool place. 

 The proportions of the various constituents of the pickling solutions are subject to 

 rather wide variation, and in general it may be said that the higher the temperature of 

 the storage room, the more concentrated must be the pickling solutions to insure 

 satisfactory preservation. 



BUTTER. Butter is usually salted with sodium chloride to impart 

 the desired taste, and this salt also acts to some extent as a preservative 

 by increasing the osmotic tension of the moisture remaining in the butter. 

 Antiseptics such as boric acid, saltpeter, salicylic acid and formaldehyde 

 have been employed in the preservation of butter, the first-mentioned 

 appearing to be the most satisfactory. One half of i per cent of boric 

 acid incorporated with high-grade butter previous to storage greatly 

 delays rancid change. Fresh milk and cream are also sometimes treated 

 with antiseptics such as formaldehyde, but the use of any chemical pre- 

 servative whatever in these dairy products is unnecessary and generally 

 disapproved. 



PREPARED VEGETABLE AND FRUIT FOODS. These foods are some- 

 times preserved by vinegar, sugar or alcohol, the presence of which is of 

 course very evident to the consumer. Other substances less readily 

 detected, such as sulphurous acid and sulphites, boric acid, salicylic acid, 

 benzoic acid and sodium benzoate, and formaldehyde, are also employed 

 in foods which must be kept some time after exposure to the air. These 

 substances are incorporated with the food before it is packed, and serve 

 to prevent the activity of microorganisms which gain access to it. 



THE NUTRITIVE VALUE OF PRESERVED FOODS. 



The nutritive value of a food depends upon the amount of utilizable 

 food principles it contains. The food-principle content can be readily 

 measured by chemical analysis, and in general there is no important dif- 

 ference between a preserved food and the corresponding fresh food in 

 this respect. The utilization of the food principles, however, depends 

 upon a number of factors and may be greatly influenced by individual 

 peculiarities of the consumer. One important factor in the utilization 

 of a food, and probably the most important factor in determining its 

 market value, is palatability. In general, preserved foods are pleasant 

 to the taste when eaten at intervals, but upon prolonged daily ingestion, 

 the appetite for them fails and they may even become distasteful. It 

 would therefore appear to be erroneous to regard preserved foods as in 



