580 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



to cool, before the spring is removed. The fruit then gradually contracts 

 as it cools, and the cap is kept pressed down on the rubber ring by 

 suction of the vacuum thus created. To open the bottle it is best to admit 

 air by piercing the lid, if metal, or by displacing the rubber ring. The 

 newest form of rubber ring is that shown in fig. 160, which has an extra 

 lip of rubber, and in order to open the vessel it is only necessary to pull 

 the lip, which enables air to again enter the bottle and so release the cap. 



In placing these bottles of fruit in the kettle or vat, care should be 

 taken that the bottom of the bottle does not touch the bottom of the 

 kettle, since the metal being so much hotter than the water above, the 

 lower fruit might burst or pulp before the vacuum is completed. This 

 may, however, be easily prevented by having a false bottom, perforated, or 

 placing a net of galvanised wire in the kettle and putting the bottles or 

 jars in a wire stand, as shown in the illustration.* 



The history of the system of excluding the air by creating a vacuum dates 

 back to early in the last century, when the French Government offered a 

 prize for the machine which should enable foodstuffs to be kept for an in- 

 definite period in as far as possible an unaltered condition, and a French 

 cook, Appert by name, was the first to keep foods fresh by the exclusion 

 of air. A great improvement on his somewhat primitive method is now 

 available in the German apparatus figured on p. 581. This consists of a 

 large kettle, through the lid of which a thermometer is set. The material 

 having been placed in jars, whether glass or earthenware, is covered with 

 a cap of glass or metal, resting on a rubber ring, and is then placed on a 

 stand, as shown in fig. 163. This stand consists of a wooden base, having 

 a central shaft terminating in a handle. Collars slide up and down the 

 shaft, and can be fixed by pins in any position. From these project springs, 

 which, pressing on the top of the cap, hold it in position until all the air 

 in the bottle has been exhausted. The stand, with the bottles upon it, is 

 then removed from the kettle and left to cool. 



The kettle is also supplied with a steamer, which, as will be seen from 

 the illustration, consists of a smaller but similar vessel, perforated both 

 at the bottom and round the sides. This is not only useful for steaming 

 certain forms of fruit before they are dried (see p. 570), but it has also 

 been found to be a better way for preparing vegetables rather than boiling 

 them in water by the old-fashioned method, since by the latter means the 

 vegetables lose a considerable proportion of their nourishing properties, 

 and if they are put into the glasses uncooked they fall together into a 



* In some larger factories there is an apparatus for instantaneously sealing jars, 

 bottles, and pots by vacuum cold process ; but although it has many advantages the 

 initial cost is prohibitive for small users. 



Fig. 161. — Wire Tray and Stands. 



