THE PRESERVATION OF WOOD AND METAL 253 



being formaldehyde. The vast quantity of milk consumed by 

 young and old, sick and well, makes the use of formaldehyde 

 a serious menace to health, because no constitution can endure 

 the injury done by the constant use of preservatives. 



The most popular and widely used preservatives of meats 

 are borax and boric acid. These chemicals not only arrest 

 decay, but partially restore to old and bad meat the appear- 

 ance of freshness ; in this way unscrupulous dealers are able 

 to sell to the public in one form or other meats which may 

 have undergone partial decomposition ; sausage frequently 

 contains partially decomposed meat, restored as it were by 

 chemicals. 



In jams and catchups there is* abundant opportunity for 

 preservatives ; badly or partially decayed fruits are sometimes 

 disinfected and used as the basis of foods sold by so-called 

 good dealers. Benzoate of soda, and salicylic acid are the 

 chemicals most widely employed for this purpose, with coal- 

 tar dyes to simulate the natural color of the fruit. 



Many of the cheap candies sold by street venders are not fit 

 for consumption, since they are not only made of bad material, 

 but are frequently in addition given a light dipping in varnish 

 as a protection against the decaying influences of the atmos- 

 phere. 



The only wise preservatives are those long known and 

 employed by our ancestors ; salt, vinegar, and spices are all 

 food preservatives, but they are at the same time substances 

 which in small amounts are not injurious to the body. Smoked 

 herring and salted mackerel are chemically preserved foods, 

 but they are none the less safe and digestible. 



235. The Preservation of Wood and Metal. The decaying 

 of wood and the rusting of metal are due to the action of air 

 and moisture. When wood and metal are surrounded with a 

 covering which neither air nor moisture can penetrate, decay 



