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diminishing expenditure on one article, they allow of some other enjoyment which was before unattainable. A reduction on quantity permits indulgence in superior quality. In the present instance, the importance of economy is particularly great, since it is applied to matters of high price, which constitute one of the daily meals of a large portion of the population of the earth.
That in cookery also, the power of subjecting for an indefinite duration to a boiling heat, without the slightest dependition of volatile matter, will admit of beneficial application, is unquestionable.
On Ultramarine, and the Methods by which its Purity may be ascertained. By R. Phillips, FRS. L. and E.
BEFORE the time of Margraff, whose analysis of lapis lazuli was published in 1768, the colouring matter of this mineral was supposed to be copper; according to the chemist just mentioned, as quoted in Klaproth's analyses, vol. i. p. 163, lapis lazuli consists of oxide of iron, silica, lime, and its sulphate, omitting any notice of the alumina which it contains in very considerable quantity, and without stating the proportions of the ingredients enumerated as its constituents.
Rinmann and Cronstadt have also mentioned the composition of this mineral, but their statements are so inaccurate as to require no further notice. According to Klaproth, lapis lazuli consists of
With respect to the colour of this substance, Klaproth observes, that " though the researches of Margraff have refuted the opinion formerly received, that the blue colour of the lapis lazuli originated from an admixture of copper; and though it has been demonstrated that the colour of this fossil is owing only to iron, yet its other constituent parts have not yet been determined with due accuracy."
Now as neither the protoxide nor peroxide of iron could be suspected of imparting a blue colour, it is singular that Klaproth
should not have alluded to this circumstance, and have suggested the nature of the combination by which iron or its oxides might, with the other constituents, produce the blue colour in question.
The analysis of MM. Clement and Desormes, (Annales de Chimie, t. 57, p. 317), shows, that although lapis lazuli may yield oxide of iron on account of the pyrites it contains, yet ultramarine prepared from it is perfectly free from any; and before I was aware that they had determined this point, I had arrived at the same conclusion, and have repeated many of their experiments; and, as far as I have gone, my results and theirs agree.
According to the chemists just quoted, the colouring matter of ultramarine is not destroyed by a moderately strong red heat, remains unchanged by ammonia, and when heated in solutions of potash and soda. Acids, however, destroy the colour in a few minutes, and this effect is produced even by acetic acid, as well as by the nitric, muriatic, and sulphuric. They also state, and correctly, that solution of sulphuretted hydrogen has no effect upon the colour. According to their analysis, ultramarine con
It is remarkable that MM. Clement and Desormes have offered no conjecture as to the nature of the colouring matter; and it was the wish to ascertain this that first induced me to turn my attention to it.
Although I have been totally unsuccessful in attaining the object of my pursuit, yet I have thought it might not be useless to state the experiments which I have made, more especially as the colour is extremely dear, therefore likely to be adulterated and I am enabled to point out ready methods of determining its purity, and detecting the nature of any fraudulent admixture.
I am inclined to believe from the results of the experiments of MM. Clement and Desormes, as well as my own, that the colouring matter of ultramarine is a peculiar substance. I must, however, repeat, that I have obtained no direct proof of it. M. Thenard, alluding to the analysis of MM. Clement and Desormes, observes (Traité de Chimie, t. ii. p. 205), "Comme ils ont eu, dans cette analyse, une perte de 0-8, il faut en conclure que quelques principes leur ont nécessairement échappés. Ces principes ne joueraient-ils pas un rôle remarquable dans la coloration du fazulite? Cette opinion paraîtra probable, si
l'on considère que toutes les autres pierres doivent leur couleur à une matière colorante. On pourrait soutenir, à la vérité, que la silice, l'alumine, la chaux, la soude, quoiqu' incolores, sont susceptibles de former un composé coloré; mais il faut avouer qu'il serait fort extraordinaire qu'il n'y eût qu'un composé de ce genre parmi ces pierres; et cependant c'est à cette conséquence qu'on serait conduit en admettant qu'il n'existe point de principe colorant particulier dans le lazulite: aussi M. Vauquelin croit-il que cette pierre contient de l'oxide de fer."
Although in the 34th vol. of the Annales de Chimie, Guyton also attributes the colour of ultramarine to iron, I need hardly again state, that ultramarine contains no oxide of iron, and, therefore, the opinion of the last-mentioned chemists, although meriting the highest attention, cannot be considered as well founded. Indeed the lapis lazuli examined by Klaproth contained only 3 per cent. of oxide of iron, and this, supposing it capable of affording a blue colour, could hardly be admitted to yield the intense blue of the lapis lazuli.
When any coloured earthy substance occurs, the first and most natural supposition is, that the colour is owing to the presence of a metallic oxide. There is however great difficulty in admitting this colouring matter to be a metallic oxide; for when it is destroyed by an acid, we may suppose one of several cases to happen, first, that the loss of colour is the result of the mere act of solution, as when we obtain a colourless solution by dissolving peroxide of mercury in nitric or muriatic acid: this, however, can hardly be the case with the colouring matter of ultramarine; for we do not by the addition of potash reproduce a blue substance; whereas from pernitrate of mercury, the oxide is precipitated possessing its original colour.
It may be supposed that the solution of ultramarine in acid is attended with the evolution of oxygen, and consequent loss of colour; but in this case one of three things would happen ; first, that oxygen would be evolved in the state of gas, as when peroxide of manganese is heated in sulphuric acid; secondly, that carbonic acid would be formed and evolved with effervescence, as when peroxide of manganese is decomposed and dissolved by binoxalate of potash; or, thirdly, that when put into muriatic acid, chlorine would be evolved; the fact, however, is, that no one of these circumstances occurs.
On the other hand, it is possible that the peculiar colouring matter of the ultramarine may acquire oxygen during solution, and thus lose its usual appearance; to this, however, there is one experiment in direct opposition; viz. that sulphurous acid which readily absorbs oxygen, but does not impart it, destroys the colour of ultramarine as completely as nitric acid, which might be supposed to oxidize it.
When nitric acid is added to ultramarine, the colour is quickly destroyed, and a slight smell of sulphuretted hydrogen is New Series, VOL. VI.
[JULY, perceptible; it might, therefore, be supposed that the colouring matter is the sulphuret of some peculiar metal. To try whether the colour could, upon this supposition, be reproduced, I added sulphuretted hydrogen both to the solution and the colourless resi→ duum, but no restoration of colour was effected by this or any other mode which I could devise. The only remaining supposition with respect to the metallic nature of this colour to which I shall allude, is the possibility that it may be in the metallic state. This, however, can hardly be the case, for if the colour be lost by oxidation, then when acetic acid produces the effect, hydrogen must be evolved from the decomposition of water; but this does not occur.
Although it is possible, as M. Thenard has stated, that colourless bodies may, by combining, form a coloured compound, I confess I rather incline to the opinion, that lapis lazuli owes its colour to a peculiar non-metallic substance; and I recommend the subject as worthy of the attention of chemists.
I shall now briefly state the methods of detecting various substances, which may possibly be employed for adulterating ultramarine.
Although we may almost venture to pronounce ultramarine to be genuine, which, in a few minutes, loses its colour when put into an acid, leaving insoluble matter of a dirty-white colour, and affording a colourless solution, I shall nevertheless mention certain bodies which it is probable may be mixed with ultramarine, and the methods by which they may be detected.
Blue Verditer-If this carbonate of copper be mixed with ultramarine, it may be ascertained by heating the suspected colour on a piece of silver or platina foil in a spirit lamp. If there be any verditer present, the mixture will become almost immediately greenish, and eventually black. The degree of alteration of colour will of course depend upon that of the adulteration.
Genuine ultramarine loses its colour totally by being put into an acid, no effervescence is excited, a deposit remains of dirtywhite colour, and a colourless solution is obtained which gives only a slight and colourless precipitate with ammonia; so that verditer, or any other cupreous compound, may also be detected by putting the colour into an acid. If a blue or green solution be obtained, and if ammonia added to it in excess gives a deepblue solution, or if a drop of the acid solution leave a deposit of copper upon iron, it follows that some preparation of copper was present; and if the admixture of verditer be considerable, the evolution of carbonic acid will be evident.
Prussian Blue. Genuine ultramarine suffers no change of colour by being heated, but if it contain prussian blue, its colour will be much darkened by heat; if also the genuine colour be boiled in a solution of potash, its intensity and brilliancy is rather increased than diminished; but if it contain any admixture of prussian blue, the colour will become browner, and the
solution, if not too strongly alkaline, will afford a blue precipitate when added to a solution of iron.
Indigo. This substance when heated in a spirit lamp readily rises in the state of purple vapour. Sulphuric acid, even in its concentrated state, does not destroy its colour, and, therefore, the presence of indigo is very readily ascertained.
Smalts. The colour of smalts resembles that of ultramarine in resisting the action of heat; but as it is not destroyed by any acid, and as the colouring matter of ultramarine is, any admixture of smalts will be easily discovered.
Colour prepared from Oxide of Cobalt and Alumina.-This compound, which greatly resembles ultramarine in appearance, although its colour is not quite so bright and intense, may be distinguished from it, by remaining unacted upon by acids precisely like smalts. Heat does not readily change its colour, but if a drop of solution of carbonate of potash be added to it on platina foil in the flame of a spirit-lamp, it is readily blackened; an effect which is not produced upon ultramarine.
On the Geology of Devon and Cornwall.
(Continued from vol, v. p. 184.)
Inferior Slate.-At and near its immediate contact with the granite appears as a somewhat indistinct and ill characterized gneiss, in some beds of which the felspar so predominates that they have been termed slaty felspar. Judging, however, from their less ready fusibility, from the large proportion of metallic oxides (iron and manganese) which they contain, and from the examination of many specimens from various quarters, we shall, I think, approach nearer to strict accuracy by regarding these as compact felspar intimately mixed with mica (or rather with chlorite) and quartz. To the geologist, who seeks the aid of mineralogy and of chemistry, examples of this intimate penetration of one simple mineral by another (so, as in many cases, to alter very considerably the external and empirical characters of that which yet predominates) must be familiar. Many subordinate beds of the earlier greenstone formation exhibit every stage of a similar phenomenon, and an accurate examination would probably show, that most of the substances named petrosilex, corneenne, saussurite, jade, and even flinty slate, are in fact only admixtures of this nature, in which felspar varying from its more compact and semitransparent to its earthy and granular form, is uniformly and intimately penetrated by some