10 BULLETIN 196, U. S. DEPAKTMENT OP AGEICULTUEE. 



basket of cans to a cooling tank, or by spraying with water in the air. There is less 

 difference in the results obtained by different methods of applying either heat or 

 cold than some claim; the important point is to accomplish these steps quickly. 



In canning operations the product, salt, sugar, or other seasoning, and water are 

 the only materials used. No hardener, bleach, or preservative is employed, and in 

 commercial canning there never was as much preservative used as is common in the 

 household operation. Saccharin and sulphites were formerly used in corn and peas, 

 but their use has now been practically discontinued; on the other hand the practice 

 of selling a "canning compound" to housewives still continues, and will only cease 

 when the nature and effects of such chemical preservatives are known, and the lack 

 of necessity for their use is appreciated. 



CONTAINERS. 



The first container used was the ordinary glass bottle with a comparatively small 

 mouth and closed with a cork. The next step was the use of a resinous wax to cover 

 the cork. The bottle was modified to the more convenient or jar form, and a groove 

 run around the top so that a tin cap might be sealed in place with wax. This method 

 of sealing was common in domestic canning until about 1890. The metal screw cap 

 with the rubber ring and various other devices, most of which depend on a rubber 

 or fiber joint to exclude the air, have been introduced since that date. The glass 

 jar is largely used in domestic canning, but not commercially, as it is heavy, breaks 

 easily, can not be handled by automatic machinery, will not stand hard processing 

 without special precautions, and increases freight rates. Glass containers are used 

 for preserves, for spiced and pickled fruits, and for the limited canning for which 

 the consumers are willing to pay a fancy price. Very recently improvements have 

 been made in glass jars and the methods of sealing, which may extend their useful- 

 ness, especially to such products as can not be preserved to the best advantage in tin. 



The earthenware jar was brought out to offset the liigh cost of the glass jars; some 

 of these were glazed inside, some outside, and some on both sides. They were gener- 

 ally sealed with a tin cap by means of wax, though a few had earthen tops. Varioua 

 forms were given to these jars, and some may still be found which have been in use 

 for many years in rural districts. The earthenware jars had only one advantage over 

 glass, that is in cost, but they had the disadvantage of having blow or sand holes. 

 The earthenware jar is not used to any large extent in commercial canning, though 

 some are iised to pack bulk jams and stock for preserves, etc. 



The tin can is preeminently the container used in commercial canning, and it is 

 also iised to a very large extent in home canning. Those used for the latter purpose 

 retain the deep ring about the opening for the insertion of caps and sealing with wax; 

 these are commercially known as wax-top cans. In commercial canning solder is 

 used exclusively for sealing stud hole or cap cans. The tin can has undergone a 

 number of changes. The first cans had flush sides and ends, or plumb joints; these 

 gave way to the stamped-overlapped ends, and all inside solder has been superseded 

 by lock seams and outside soldering. Most solder caps are hemmed, so that only 

 the amount necessary to seal is used. The solder can has been superseded in many 

 cases by the open top, or so-called sanitary can, and in this case the sealing is done 

 by double seaming on the top, no solder being used on the can except in making the 

 side seam. The former objections to acid and solder, on the ground that they con- 

 taminated the foodstuffs, have thus been largely overcome. 



The most recent improvement in the tin can is the inside coating or lacquering. 

 This type of can is known to the trade as the "enamel Hned" can. Various coatings 



