From the stems, bark, fruits and leaves receive not only dyesbut also dozens of other useful substances. Surprisingly, plants and contain such organic compounds, which are able to protect the metal from corrosion.
Imagine that bulky steel item must be clean and free from rust. Not to RUB it emery cloth. So, we need a chemical method, for example, etching with acid. But if you omit the item in the solution of any acid that removes rust, you will inevitably be dissolved and the metal part as it will protect it from contact with acid?
The answer is clear: we need a solution that removed the rust, but not touching the metal itself. Such etching solutions are already used in practice. In addition to the acid in them is another important additive is a corrosion inhibitor. It is a substance that dramatically slows down the dissolution of the metal, but almost never bothers to dissolve its oxides and hydroxides, i.e., the corrosion products.
Those inhibitors, which are used in factories, obtained mainly by synthetic means. Among them, hexamethylenetetramine, in pharmacies sell it under the name of"+". If you put a parallel experience - two identical iron object to put in two test tubes with a weak solution of hydrochloric acid, and requested to add one little pounded urotropine, the difference soon can be seen with the naked eye: in vitro dissolution inhibitor metal will go much slower.
But we were going to remove the corrosion inhibitors from plants. This will now address.
Of wild plants for our experiments suitable celandine, hen and dymjanka of the poppy family, marsh mallow family Malvaceae and yarrow from the family Compositae; we need their leaves and stems. Note that many of these plants in dry form are available in pharmacies. For experiments need multiple instances of the plants. Warning careful attitude to nature remain in force, as well as the proposal to consult with the teacher of biology or to stock up on vascular plants.
To retrieve inhibitors can be rented and some cultivated plants is probably easier. Suitable for experiments the leaves and stems of potatoes and tomatoes. There is a sense to wait until the ripen the harvest and take for experimentation unnecessary remnants of plants.
The leaves and stems of wild or domesticated plants chop with a knife and pour weak concentration of not more than 5 per cent, solution of hydrochloric acid. If you use a pharmacy hydrochloric acid, then dilute it with water to about half. Leave filled with solution a lot for a few days in a sealed container, so that the extraction was as fully as possible; weeks, at least, should be enough. When the extract is ready, make the pickling solution for rusted parts. If rust is very much, the composition of the solution (for convenience - by volume): 5 parts extract 40 parts of concentrated hydrochloric acid and 75 parts of water. If rust is not very much, you have to take 10 parts extract, and about 20 parts of acid; the amount of water can also slightly increase.
In such solutions, you can immerse the rusty parts. They soon will be shiny like brand new, and the metal they almost never go into the etching solution.
But what is the substance in plants that were found, as well protect the metal from corrosion? This complex compounds, alkaloids, polysaccharides, proteins, mucous and tannins. All of them, though in different degrees, have the ability to adsorb on the metal surface and fixed on her, and consequently, they prevent a direct contact of the metal with acid. With rust they do not wish to unite, so it dissolves in the acid without interference.