Carl Wilhelm Scheele (1742-86)

On Manganese and its Properties

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6. (a) One ounce of pure spiritus salis was poured on half an ounce of finely-ground manganese. After this mixture had stood one hour in the cold, the acid had assumed a dark brown colour. Part of this solution was poured into a bottle, which was left open in a warm place. The solution gave off a smell like warm aqua regis, and after a quarter of an hour it was clear and colourless as water, and the smell was gone. (b) The remainder of the brown mixture was set to digest, in order to see whether the marine acid would saturate itself with manganese. As soon as the mixture became warm, its smell of aqua regis became considerably augmented, and an effervescence also arose, which continued till the following day, when the acid was found to be saturated. On the residue which it had been unable to dissolve, there was again poured one ounce of spiritus salis, whereupon all the above-mentioned phenomena occurred, and the manganese became completely dissolved, except a little siliceous earth.

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23. The sixth paragraph shews the behaviour of manganese with marine acid. In this case it is not so easy to understand at first whence the manganese has obtained its phlogiston; nothing combustible is added here, and nevertheless the complete dissolution of the manganese can be effected without heat. In fact, there occurs here a phenomenon which proves that phlogiston is certainly present in marine acid--a property which one would have attributed to nitrous acid, since chemists, subsequent to STAHL, have believed that this principle is required in considerable quantity as one of its constituents. That, however, we may now reverse and attribute to marine acid.

When marine acid stood over manganese in the cold it acquired a dark reddish brown colour (6,a). As manganese does not give any colourless solution without uniting with phlogiston, it follows that marine acid can dissolve it without this principle. But such a solution has a blue or a red colour (14, No. 4). The colour is here more brown than red, the reason being that the very finest portions of the manganese, which do not sink so easily, swim in the red solution; for without these fine particles the solution is red, and red mixed with black makes brown. The manganese has here attached itself so loosely to acidum salis that water can precipitate it, and this precipitate behaves like ordinary manganese. When, now, the mixture of manganese and spiritus salis was set to digest, there arose an effervescence and smell of aqua regis (6,b).

In order clearly to apprehend this novelty I took a retort containing a mixture of manganese and acidum salis. In front of the neck I bound a bladder emptied of air, and set the retort in hot sand. The bladder became distended by the effervescence in the retort. When the acid no longer effervesced, which was an indication of its saturation. I removed the bladder, and found that this air had coloured it yellow, as if by aqua fortis, but did not contain any trace of aer fixus; it had, however, a quite characteristically suffocating smell, which was most oppressive to the lungs. It resembled the smell of warm aqua regis. The solution in the retort was clear, inclining to yellow, which last mentioned colour was caused by its containing iron. If one wishes to be convinced that this dissolved manganese contains phlogiston, let him precipitate the solution with alkali tartari, edulcorate the precipitate, and then proceed therewith as is described in 15,a,b,c. But whence has this manganese obtained phlogiston? From acidum salis. Here we cannot have recourse to heat, because the solution becomes clear without it, only it must stand several hours in the open air. What happens to the solution is as follows: The manganese is first attracted by the marine acid, whence a brown solution arises. By the help of the acid this dissolved manganese acquires a strong attraction for phlogiston (14, No. 2), and actually draws it to itself from the particles of acid with which it is united. This part of the acid, which has thus lost one of its constituents and is only very loosely united to the now more phlogisticated manganese, is driven out from its earth by the remaining marine acid which has not yet suffered any decomposition, and appears then, with effervescence, as a highly elastic air, or similar fluid; the brown colour has then disappeared and a water-clear solution resulted.

24. This marine acid, deprived of phlogiston as one of its constituents, unites with water in very small quantity; and gives the water a slightly acid taste; but as soon as it comes in contact with a combustible matter it becomes again a proper marine acid. In order to investigate the properties of this air it is best to put it to the test in the elastic state. Ordinary marine acid is mixed with finely-ground manganese, in any chosen quantity, in a glass retort which is placed on warm sand; small bottles which hold about twelve ounces of water are employed as receivers; about two drachms of water are put into each bottle, and the joints are not luted except by means of grey paper wrapped round the neck of the retort, and on this the bottle is fixed. When a bottle has remained a quarter of an hour or more, it is found, according to the quantity of the elastic acid in the receiver, that the air in it assumes a yellow colour; the bottle is then removed from the retort.

If the paper luting has held tight, a part of the air escapes with force; a previously fitted cork is then immediately inserted into the bottle, and another bottle is fixed to the neck of the retort in its stead. In this way several bottles can be partly filled with dephlogisticated marine acid. It is to be noted that the retort must be placed in such a position that in case drops should rise into the neck they can flow back. The water in the bottle serves this purpose, that, should any vapour of muriatic acid pass over, it may have this water to which it may betake itself. I take more than one bottle so that it is not necessary for me to start a new distillation for each experiment I make. It is not advantageous to fill large globes, as a good deal of the acid escapes into the air every time they are opened.

25. Whatever was experimented with in this dephlogisticated marine acid was hung on a glass tube which I fastened into the cork. (a) The corks in the bottles became yellow, as from aqua fortis, and during the distillation the luting was likewise attacked. (b) Blue litmus paper became almost white; all vegetable flowers--red, blue, and yellow--became white in a short time; the same thing also occurred with green plants. In the meantime the water in the bottle became changed to a weak and pure marine acid. (c) The former colours of these flowers, as well as those of the green plants, could not be restored either by alkalies or by acids. (d) Expressed oils and animal fats, when they hung as drops on the glass tube or were rubbed on it, became in a short time tough like turpentine. (e) Cinnabar became white on the surface, and when the piece was washed in water a pure mercurius sublimatus solution was obtained, but the sulphur was not altered. (f) Iron vitriol became red, and deliquesced. Copper and zinc vitriols were unaltered. (g) Iron filings were put into the same bottle and they dissolved. This solution was evaporated ad siccum and distilled with addition of oil of vitriol, when a pure marine acid, which did not dissolve gold, again passed over. (h) All metals were attacked, and with gold it is noteworthy that its solution in this dephlogisticated marine acid forms with alkali volatile an aurum fulminans. (i) When spiritus salis ammoniaci, prepared with lime, hung in drops on the tube, there arose a white cloud, and a quantity of air bubbles escaped from the drops, which gave off a smoke when they burst asunder. (k) Alkali fixum was changed into sal commune which decrepitated on charcoal, but did not detonate. (l) Arsenic deliquesced in these vapours: (m) Insects immediately died in them; (n) and fire was immediately extinguished in them.

26. This proves sufficiently the great attraction which dephlogisticated marine acid has for the combustible. It is possible that STAHL obtained such a dephlogisticated marine acid by means of iron, as he conludes from the yellow colour on the cork, and imagined that the marine acid was changed into nitrous acid. If a mixture of manganese, spiritus salis or spiritus vitrioli, and alcohol vini is digested several days in a well-closed flask, and thereafter gently distilled, there arises no effervescence, but spiritus vini passes over; it has, however, and this is noteworthy, a strong smell of aether nitri. The residue in the retort has lost its acid, and is saturated with manganese. If metals, sugar, turpentine, or linseed oil are added to a mixture of ground manganese and marine acid there arises no dephlogisticated marine acid; for here there is sufficient combustible present with which this elastic acid can combine. With mercury it is noteworthy that a good deal of it also goes into the solution, from which it can be obtained by crystallisation, and behaves like corrosive sublimate. If leaves of pure gold are put into a mixture of ground manganese and pure acidum salis, it is found afterwards that this solution contains gold, as well as manganese, dissolved.