,56 MADRAS FISHERIES BULLETIN VOL. XIII, 



absolutely air-tight either by the usual washer or by an external 

 wash of thin solder which is generally applied automatically. 



42. The locked side seam with an external wash of thin solder, 

 may be introduced into the ordinary fish tins (rectangular or 

 cylindrical) when the body is formed from the strip ; this will give 

 a much neater and stronger seam and save solder. An attempt 

 was made at Beypore to introduce it, but the locally made tool ^was 

 insufficient and none was then — during the war — obtainable from 

 England. 



43. For all cylindrical tall cans, i.e., those in which the height is 

 equal to or greater than the diameter, this ' sanitary ' or semi- 

 solderless method is a great improvement, as the cylindrical shape 

 lends itself to the method, and the can is both stronger, neater, and 

 cheaper. 



44. But to render any can fully ' sanitary ' in the sense not 

 only of dispensing with solder and acid or other fluxes and of more 

 complete hermetical sealing and consequent diminution of spoil- 

 age, but of preventing any action of the contents on the metal, 

 something more is needed, especially with certain classes of goods 

 such as prawns and shell fish, marinated fish, fruits, jams, jellies, 

 etc. ; even ordinary fish, when not put in oil, are the better for pro- 

 tection from immediate contact with the tin plate. In all these 

 cases certain constituents of the contents, e.g., the sulphur or phos- 

 phorus in prawns, the acetic acid (vinegar) in marinated fish, the 

 acid in fruits and jams, act upon the metal of the containers ; 

 prawns rapidly blacken and though not perhaps poisonous are so 

 unsightly as to be unsaleable or rejected by the consumer; acid 

 jellies also blacken and dissolve the tin from the plate. So far 

 nothing has been successful in absolutely preventing such action, 

 but lacquered or so-called ' enamelled ' tins are now largely used. 

 Lacquered plate is now sold in which the lacquer is so completely 

 united with the metallic surface that cans can be made from the 

 flat plates without the lacquer cracking or peeling, but this lacquer- 

 ing is usually very thin, and is often entirely removed if the cans 

 are boiled in even a weak solution of sodium carbonate for the 

 purpose of removing grease. In other practice, as at Beypore, it is 

 usual to apply the lacquer (usually an oil varnish with turps) to the 

 interior of the formed can, either by painting or spraying ; the can 

 is then baked to harden the lacquer, and the process is generally 

 repeated, forming ' double lacquered ' tins. The baking is done 



