DISINFECTANTS AND DISINFECTION. 185 



The percentage of benzoate preservative is likely to vary because of its 

 volatile nature; canners quite generally add an excess knowing that much 

 of it will be carried off with the vapors escaping during the heating process. 

 As a result it follows that products declared to contain o.i per cent, of benzoate 

 may upon chemical examination show the actual amounts to range from a 

 mere trace (0.05 per cent, to 0.5 per cent.). 



Next to benzoate, salicylic acid is perhaps the most common food pre- 

 servative, used much like benzoate, in strengths varying from o.io to 2.5 

 per cent. It is frequently added to beers, cordials, vidnes and foods (4 to 8 

 grains to the pint) containing sugars. It is also used as a surgical dressing, 

 but other less irritating wound disinfectants are given the preference. 



Crude pyroligneous acid is used as a meat preservative. This acid is 

 obtained by the destructive distillation of wood and contains creosote and 

 other tarry matter and imparts the odor and taste of smoked products. 

 Meats, fish, etc., are immersed in a solution of this acid, dried and sold as 

 smoked. This constitutes the "quick" or "dip" method of smoking meats 

 as compared with the usual slower method of exposing the meats to the 

 smoke of slowly burning wood. 



The following are a few of the less commonly employed preservatives: 

 Fluorine compounds are used in strengths of from 0.03 to 0.02 per cent. 

 Alum is sometimes used in pickling vegetables and meats (brine) because 

 of the hardening effects produced. Copper sulphate is much used in 

 pickUng cucumbers, peas, string beans and other green vegetables for the 

 purpose of deepening the green color. Sodium and calcium carbonate are 

 sometimes added to cider and wine to check the souring process (by com- 

 bining with the fruit acids) . Formic acid is a powerful preservative. 0.014 

 to 0.08 per cent, retards fermentation. Saccharin, sucrol and dulcin are 

 sweetening as well as preserving agents. Peroxide of hydrogen is used as a 

 preservative. It is also a deodorant. The use of saccharin in food is no 

 longer permissible in the United States. 



6. Insecticides and Other Pest Exterminators. 



The farmer, fruitgrower and florist have many enemies belonging to the 

 insecta and to other divisions of the animal kingdom, which interfere with 

 the productiveness of crops. The remedies employed against these pests 

 are numerous. We shall mention only a few of the more useful ones, ex- 

 plaining their action very briefly. They may be grouped into powders, 

 gases, sprays and washes. 



A. Pcfwders. — These may be applied by the "pepper box" method, the 

 material being placed in a box, usually of tin, with perforations, through 

 which the powder sifts on shaking. Or a blowing device may be used, 



