6 



BULLETIN 240, U. S. DEPARTMENT OF AGRICULTURE. 



cool for a few minutes in air until the cap becomes concave, as this 

 is said to hold the cap on tight and helps to make it water-tight. 

 Obviously, it is of utmost importance that the caps be water-tight, 

 since they are submerged in water during cooling, and if not tight 

 the milk may become infected by polluted cooling water. 



When bottles are submerged the ordinary cardboard cap is of no 

 value for pasteurization in the bottle, since water will easily pene- 

 trate during cooling. This makes it necessary to use some form of 

 patented cap, of which both specially treated cardboard and metal 

 caps are on the market. It is almost needless to state that if the edge 

 of the bottle is chipped or otherwise imperfect almost any seal cap 

 will not be water-tight during the cooling. Imperfect bottles must 

 not be used. It is claimed by the manufacturers of patented seal 







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150° F. 

 140° F. 

 130° F. 

 1 20 F. 

 no°F. 

 100° F. 



go° F. 



8o°F. 



7o°F. 



60° F. 



50° F. 



Heating period in minutes. 



Fig. 2. — Variations in temperature in different parts of quart bottles of water during the 



process of pasteurization in the bottle. 



caps that they are tight on perfect bottles. It would be advisable, 

 however, for the dairyman to test the tightness of his caps by the 

 following method : Fill the milk bottle with a 0.05 per cent solution 

 of barium chlorid (BaCL). The barium-chlorid solution should be 

 made up with distilled water, since the sulfates present in ordinary 

 water will cloud the solution. Cap the bottles in the usual way 

 with a seal cap and heat to 145° F., submerge, and cool in a 10 per 

 cent solution of magnesium sulfate (MgSo 4 ). 



If any of the magnesium sulfate leaks into the bottle during cool- 

 ing the barium-chlorid solution will become cloudy, owing to the 

 formation of barium sulfate, which is insoluble. This test is very 

 delicate and will show even a slight leak. Both these chemical- may 

 be obtained at any drug store. Since barium chlorid is poisonous, 

 after testing bottles in which if has been used care must be taken to 



