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"I RON," said Uncle Paul, "is abundant and cheap; furthermore, the hottest fire in our stoves and grates cannot melt it, and it is able to withstand rather rough usage. These qualities are highly important in cooking-utensils, which must resist the action of fire without risk of melting, and have every day to undergo bangs and falls. But unfortunately this metal rusts on the slightest provocation; contact with a few drops of water for any length of time suffices to cover it with ugly red spots which eat into it and finally pierce quite through. This rapid deterioration is prevented by tinning.
"A metal is tinned by being overlaid with a thin coating of tin, which resists rust. Now bear in mind this important point, which I have already briefly touched upon: rust develops only where air is present. Also, it is promoted by various substances, such as water, vinegar, and the juice of our vegetables and fruits. Nearly all the dishes we prepare for the table tend by their mere contact to rust metals capable of rusting, and especially iron. To prevent the formation of rust, therefore, what must we do? The answer is plain: keep our food and the air from coming in contact with any metal that will rust. If this contact never occurs, rust will never form, for there will be nothing to cause rust.
"Our obvious course, accordingly, is to coat the corruptible metal with one that will protect it, and this last must fulfil two conditions: it must not be liable to rust; or, at any rate, it must be a metal that rusts with difficulty, since otherwise one ill would only be exchanged for another; and it must also be a metal from which food will contract no injurious properties. This double requirement is met by very few metals. There are, first, gold and silver, both too expensive for common use; and finally there is tin. This metal is very slow to rust, and, furthermore, tin-rust, if it ever begins to form, does not form in any quantity and has, besides, no harmful properties. Tin, therefore, furnishes us the metallic coating we need for preserving our iron utensils from rust."
"Wouldn't it be much simpler," asked Claire, "to make these utensils wholly of tin in the first place and so get rid of iron altogether?"
"There is one serious objection to such a course: tin melts easily. A saucepan of this metal would not hold out for five minutes against the heat of a handful of glowing charcoal. What would become of your stew in a cooking-utensil capable of melting like wax over the fire?"
"I see now that tin by itself would never do."
"Nor would it answer for another reason: it offers too little resistance, it bends under slight pressure, it is knocked out of shape with a blow. We must have two metals combined: iron to resist heat and stand rough usage, and tin to prevent rust. If, however, the utensil is not to go over the fire, it can in case of need be made of tin alone. Not very long ago, in the country, tableware for company use was of tin. Plates, platters, and soup tureens shone like silver on the shelves of the dresser, and were the pride of the housewife. Our measures for wine, oil, and vinegar are of tin. The use of this metal in preference to any other for utensils that are to come in contact with our food is due to its perfect harmlessness. Tin keeps its cleanness and polish and—a still more valuable property—communicates nothing injurious to the substances it touches.
"You are familiar with those wandering tinkers with sooty faces who, a kettle over the shoulder and a few old forks in one hand, go through the street, crying their trade in a shrill voice. In the open air, over a little charcoal fire, they restore rusty covers to their first brilliance, mend kettles and saucepans, and plate with tin utensils of iron and copper, to keep them from rusting. The operation is very simple: the piece to be tinned is first well scoured with fine sand, and then heated over the fire, and while it is still warm a little melted tin is rubbed over the surface with a wad of tow. The tin takes fast hold of the underlying metal and covers it with a thin layer which will not come off with rubbing. That is what is known as tin-plating."
"Then what we commonly called tin," said Marie, "is really iron covered over with tin?"
"Yes, it is tin-plated iron, and is made by plunging thin sheets of iron into melted tin. These tinned sheets, light and strong at the same time, polished and rust-proof, serve for the manufacture of numberless utensils. The outfit of our kitchens consists in great part of tinware."
"But it consists also of copper-ware," remarked Jules.
"Yes; but copper has very dangerous properties which call for the utmost caution on our part. Iron-rust is harmless, I might even say healthful, in limited quantities. Little children deficient in bodily vigor are sometimes made to drink water impregnated with a small quantity of rust from a few old nails in the bottom of the water-bottle. Nothing, then, is to be feared, so far as our health is concerned, from the rusting of iron; it is coated with tin, not as a safeguard against danger, but to give the metal cleanliness and greater durability.
"Copper-rust, on the contrary, is a violent poison. This rust, or verdigris, is all the more dangerous in that it develops with extreme ease when copper comes in contact with our articles of food, especially when the latter contain vinegar or fat. Have you ever noticed the greenish tinge imparted to the oil in lamps and to the candle-drippings on candlesticks? Well, this tinge comes from the copper that enters into the metal part of lamps and candlesticks, and is due to the verdigris dissolved in the oily matter. Our food, containing as it almost always does some slight proportion of fat or oil, contracts the same greenish tinge by remaining any length of time in contact with copper. Vinegar acquires it in a few moments. This green substance from copper, always bear in mind, is a terrible poison which cannot be too carefully shunned. The only safe course lies in constant watchfulness and in a scrupulous cleanliness that keeps all copper utensils always bright and free from the slightest indication of a green speck. For greater safety it is even preferable to use only tinned ware for culinary purposes. Proof against rust under its coating of tin, copper then ceases to be injurious, but only on condition that the tin coating is maintained intact, never uncovering a particle of the poisonous metal. As soon as the tin becomes dim and shows a little of the red underneath, the utensil should be retinned.
"Lead is no less dangerous than copper, but this metal enters very little into domestic use, unless it be for cleaning bottles. A handful of small shot shaken up in water serves excellently to remove by friction the impurities clouding the inside of the glass. This practice, however, is not free from one grave danger. Suppose a few particles of lead are retained in the bottom of the bottle and left there unobserved. Wine, vinegar, or whatever other liquid is afterward poured in, is likely to cause the lead to rust, and will thus contract properties highly injurious to health. Without any one's suspecting it there will lurk in the bottom of the bottle that is daily used a permanent source of poison. You see therefore what care should be exercised in order that not a particle of lead may be left behind after this metal has been used for cleaning purposes. Never forget that copper and lead are two poisonous metals, and that any carelessness in their domestic use may suffice to imperil our very lives."