10 BULLETIN 196, U. S. DEPARTMENT OF AGRICULTURE, 
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. . =e 
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 high 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. Various 
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 
elass, 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 used to pack bulk jams and stock for preserves, etc. 
The tin can is preeminently the container used in commercial canning, and it is 
also used 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 lined” can. Various coatings 
