LECTURE VI. CARBON. NOTES OF MATERIALS AND APPARATUS REQUIRED FOR Slips of paper dipped in alum or borax. Specimens of charcoal, diamond, plumbago, coke, &c. Diamonds turned into coke. Animal charcoal. Tincture of litmus. Materials for illustrating the process of fermentation :- of carbonic oxide. Apparatus for burning the diamond in oxygen gas. Lime-water. A burning candle to illustrate the property of flame. A jar of olefiant gas, and another of chlorine, ready to be mixed. "On The theatre was [THIS was the final lecture of the course of six, the Non-Metallic Simple Elements." very fully attended, and his Royal Highness Prince Albert honoured the audience by taking the chair. The lecturer commenced by directing the attention of his audience to the various pieces of carbon present on the table-the diamond, coke, charcoal (animal and vegetable), plumbago, and diamonds partly converted into the black amorphous form.] The first point in connection with the natural history of carbon, is the circumstance of its invariable solidity. This quality I shall have to allude to again in connection with some of the most usual functions of carbon it is one which lies at the foundation of almost every useful application of the substance. Notwithstanding this fixity of carbon, it is strange to recognise certain chemical effects capable of being produced by this element: thus, for instance, it has the power of absorbing larger bulks of various gases of removing putrid smells and certain colouring matters. Yet, (continued Mr. Faraday,) the chemical agency of carbon in an isolated state is but insignificant when compared with the wonderful energies called into play in its various combinations. To me, viewing as I do the qualities of each element in relation to its most obvious functions in the economy of the universe— speculating on what must have happened had these qualities been different to what they are-pondering over the all-wonderful foresight by which the harmonious balance of elemental powers was predetermined and is maintained-this fixity of carbon, in comparison with the volatility of its compounds, is a subject of never-failing interest and admiration. This is a subject which will prominently appear as I go on, and more especially after I shall have taken up the oxy-compounds of carbon. Of these oxy-compounds there are two-the carbonic oxide and the carbonic acid gas. As regards the first, of which we have a specimen near, it is of frequent occurrence in many common instances of combustion. All who are here probably have seen a charcoal fire, and have recognised a peculiar blue lambent flame which plays upon the ignited coal this flame is produced by the combustion of carbonic oxide. Another common instance of its occurrence is in an active limekiln; over the ignited lime there plays the same lambent flame. instances may be sufficient, without experiment, to impress upon your minds the two leading qualities of carbonic oxide gas-its inflammability and the peculiar colour of its flame. But in this jar I have some of the gas in a pure state, and can demonstrate its combustibility and peculiarity of combustion by withdrawing the stopper and applying a light. These Of carbonic oxide little is said in comparison with the general repute of carbonic acid, yet its functions in many operations are highly important: and, as regards its agency on the animal economy, the experiments of Dumas have shown that it is at least a hundred times more poisonous than carbonic acid. This is a fact which was until lately unknown; carbonic acid having been considered as the more poisonous gas. However, without repeating the experiments of Dumas, they have been propounded on such evidence as I am willing to accept as perfectly conclusive. Now, this extremely poisonous nature of carbonic oxide is a fact of great significance when we regard it in connection with certain proposed plans of illumination which contemplate the employment of this gas. In itself carbonic oxide has but little illuminating power, as you have seen; but illuminating power can be given by causing it to absorb certain particles extraneous to itself, and in the end it may be made a good illuminating source. Should this plan of illumination be carried out, it will be necessary, after the experiments of M. Dumas, to watch attentively the first results; for, although the speculative chemist should be most careful not to impede, by undue expression of vague fears, the progress of any discovery, yet, on the other hand, facts so significant as those indicated by M. Dumas should not be passed by unheeded. Accordingly, I have been made aware that in France, where matters of public health are much more studied than in England—much more taken cognisance of by the Government-competent persons are anxiously watching the first effects of the new illuminative gas, considered under a sanitary point of view, and are authorised to forbid the process on the first manifestation of a result unfavourable to health. Passing away from carbonic oxide with this short notice, we now arrive at the consideration of carbonic acid. This body, like the preceding, occurs naturally in the form of a gas, although it has been condensed into the fluid and the solid condition. This gas is the highest form of combination of carbon with oxygen, and is the one which naturally results when carbon is burned in atmospheric air or oxygen gas; it is also the gaseous result of fermentation, as can readily be made evident by the following experiment. Into a globular vessel has been put a mixture of one part sugar, four parts water, and a little yeast, — and the whole mixture having been exposed to a temperature between 70° and 80° F., the process fermentation has set in. The vessel is now filled with carbonic acid gas, as I have no doubt can be manifested. of I should preface the trial, however, by stating the evidence by which the presence of carbonic acid can be demonstrated. In the first place, then, carbonic acid gas is so much heavier than atmospheric air that it can be poured, after the manner of a liquid, from one vessel to another. In the second place it neither burns nor supports combustion-then, if agitated with limewater, the latter affords a white precipitate: chalk or carbonate of lime-in addition to which qualities it reddens turmeric and has a peculiar smell. Any gas possessing these qualities must be carbonic acid. Let us now observe whether such have been produced. [At this stage of the lecture Professor Faraday performed the usual experiments demonstrative of the great weight of carbonic acid gas, its negative qualities of neither burning nor supporting combustion, its slight |