METHODS OF FBUIT PBESEBVINCh 



579 



over and clinched round this lip by a simple machine, which revolves 

 after the manner of a potter's wheel. This forms the bottom of the tin, 

 and the top is fastened in the same way. By this method the use of 

 solder is almost abolished, but it is necessary to see that the tins are full 

 of cold, cooked fruit or vegetables, otherwise the contents would contract 

 on becoming chilled and be unusable. In larger factories the whole of 

 the tins are made on equally simple machines, and much cost is saved to 

 the proprietor. These machines are already on the English market, but 

 the system of tins with sunk heads have not yet been seen here, and this 

 is the only method by which tins can be used more than once. 



The Vacuum Process. 



By far the most popular method in Germany is the vacuum process, 

 and this is already gaining public favour in this country extremely 



RUBBER RING 



Fio. 159. — Spring for Single 

 Bottles. 



For use when the stand is not 

 employed. The spring holds 

 the cover in position until 

 the vacuum is completed. 



Fig. 160. — Opening Sterilised Bottle, 



When it is desired to open a sterilised bottle, it is only 

 necessary to pull the lip of the rubber ring, which 

 thus admits the air, and the cover becomes loose. 



rapidly. It also has an additional advantage inasmuch as it enables the 

 fruit or other foodstuffs to be cooked and the bottle secured at the same 

 operation, should it be desired. The contents are also thus sterilised, since 

 fungoid growth and other damage are always caused either by spores or 

 by the action of the atmosphere, and the spores are killed by the boiling 

 and the atmosphere excluded. 



To create the vacuum it is necessary to force out all the spare air at 

 the top of the bottle, and to prevent any more from entering. This is 

 done by placing a rubber ring between the cap and the jar, and securing 

 the latter with a spring.* The whole is placed in water sufficient to cover 

 the bottles and boiled. As the fruit expands with the heat, the air is 

 expelled above or below the rubber ring, and forms momentary bubbles in 

 the water. When the bubbles have ceased occurring, it is certain that 

 the whole air is exhausted. The bottle is removed and placed on one side 



* Glass bottles with glass caps are undoubtedly the best, but they are also the 

 most expensive method, and can only be employed for home use or when the bottles 

 are made returnable like mineral water syphons. 



