This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Banca tin is supposed the purest and best for tinning purposes. It is claimed, however, by some parties, that block-tin lining is not fully perfect, as it is porous, scaly and, like iron, unreliable. Modern science has developed nothing better for pipes and joints than block-tin yet, and the percentage of loss by leakage through its pores, furrows and breaks is not worth mentioning. We compile from scientific sources the following:
"Tin, in its pure state, is a white metal, almost as brilliant as silver. It possesses a very peculiar and distinct taste, and when rubbed between the fingers emits an extremely disagreeable odor. When bent, it produces a peculiar crackling sound and develops great heat. It is quite malleable, and can be reduced to a very thin foil; it is also very ductile, but its tenacity is so slight that it cannot be drawn into a fine wire, as other metals like gold, silver or copper. It is one of the softest metals known, and has hardly any elasticity. If fused, it crystallizes readily, and the crystals so obtained are sometimes cubical and sometimes in the form of prisms with a square base.
"Air, even when moist, has scarcely any effect on tin at ordinary temperatures. It causes the formation of a gray coating, consisting of protoxide of tin and tannic acid, which effectually preserves the metal from further alteration. Most acids, however, both mineral and vegetable, have a decided action on tin. Sulphuric acid, in a diluted state, produces but little effect on this metal; but in a concentrated state it quickly reduces it to sulphate of protoxide of tin and develops sulphurous acid. Hydrochloric acid also has but little action when diluted, but when concentrated, it rapidly dissolves tin, changing it into protochloride of tin, and evolving hydrogen. The action of dilute nitric acid is slow, but with four equivalents of water, as is the case with all commercial acids, the action is very pronounced. The metal is transformed into a white powder, which becomes insoluble in nitric acid, and the acid evolves clouds of vapor. The water concurs in this oxidation; its hydrogen unites with a portion of the nitrogen of the nitric acid to form ammonia, which is found in the liquor in the form of nitrate of ammonia. If the nitric acid is monohydrated, the tin may remain in contact with it for any length of time without undergoing the slightest alteration, but upon the addition of the smallest amount of water, a violent chemical reaction will set in, producing intense heat and sometimes flames.
"A mixture of common salt and vinegar, if boiled in a tin or a tinned vessel, will rapidly cause its deterioration. As the acetic acid of the vinegar boils at a higher temperature than the hydrochloric acid of the salt (chloride of sodium), the acetic acid combines with the salt to form acetate of soda, and leaves the hydrochloric acid in a free state to combine with the tin as protochloride of tin. Hydrated alkalies attack tin by developing hydrogen, and the products of this reaction are soluble metastannates. Oxygen produces different combinations with tin, the most important ones being the protoxide, the binoxide and the peroxide of tin, and tannic and metastannic acid. A solution of saltpetre in water, boiled in a tin, or a tinned vessel, attacks the tin and transforms it into metastannic acid.
"Tin, in its pure state, is so soft and so fusible a metal that it is of no practical use for manufacturing utensils which are subjected to heat, and for this reason it is rarely employed without admixture. Commercial tin is often impure, being contaminated with other metals introduced by fraud, or which are present in consequence of the mode of extraction from the ore. A high specific gravity is an indication of impurity, and when the color of the metal has a bluish or grayish cast, the presence of copper, lead, iron and antimony may be suspected. The purer the metal is, the more distinct is its crackle, the whiter and more brilliant is its appearance, and the less does it seem to crystallize on the surface. To obtain the metal in its purest state, it should be treated with nitric acid, which dissolves all the foreign metals it may contain, transforming the tin into metastannic acid, which can then be reduced in a crucible. The arsenic which may be present in commercial tin may amount to 1/600 part, which is too slight a proportion to have an injurious effect. In order to harden tin, it is alloyed with lead, which, in some instances, has been found present in as large a proportion as 18 and 20 per cent.
"Such an alloy, however, cannot be safely used, and for a long time tinned copper vessels have been employed instead. But these are open to serious objections, and many deplorable accidents have resulted from their use. The tin wash which is used for tinning copper vessels is never pure tin, but consists either of an alloy of lead and tin or of a mixture of tin, lead and bismuth, combined in various proportions, not only for the purpose of making the tin heavier and more durable, but also to facilitate the melting process. Tinned copper should not, therefore, be brought into contact with alimentary products of any kind, especially with syrups, which are all more or less acid. Even plain soda water, which has an acid reaction due to the presence of carbonic acid, cannot be kept with impunity in a tinned copper vessel. Especially is this the case when the tin surface is partially destroyed, as a galvanic action then appears to set in, owing to the presence of the two metals (tin and copper) in the acid beverage. While the plain carbonated water could be kept with perfect safety in a sheet-tin lined vessel, syrups could never be left in contact even with pure tin without being more or less contaminated in consequence".
Apply a drop of glacical acetic acid or a drop of nitric acid; heat; after cooling apply a drop of a 5 per cent, solution of iodide of potassium (5 parts dissolved in 95 parts of distilled water). Yellow stain when lead is present. (Robierre & Fordos).