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506 THE PHOTOGRAPHIC NEWS. [October 24,1862. best conditions, is as sensitive as can be desired, but that these conditions are difficult to secure and impossible to maintain; and that they are frequently accompanied by a host of troubles in the shape of spots, streaks, and comets, which have often well-nigh driven the photographer frantic ; whilst a bromo-iodized collodion is more uniformly rapid in action, almost entirely free from speck or spot, and more harmonious and satisfactory in general result. We do not attempt here to enter into some of the theo retical questions raised by Mr. Webb. We are content to look to the facts. Bromo-iodized collodion and iron de velopment are now almost universally used by professional photographers, who are generally tolerably quick to perceive in which direction their interest lies. We receive almost every week letters from able and experienced amateur photographers, stating that they have renounced pyro and the simple iodide, and henceforth swear by iron and a bromo-iodizer ; and not a few thank us for our persistent advocacy, which has induced them to change their faith and practice in this respect. We repeat, as we have often done: let all who have time try each method, each under its own best conditions ; and let those who have not time for experi ment look to the results in the works of the best operators. In either case there will remain little room for further indecision. Scientifir 6ossip. Fob. some months past a paper war has been waged in peri odicals more especially devoted to pharmacy, respecting the employment of methylated spirits in the preparation of tinctures and extracts, one party advocating its use and urging the proper authorities to legalise its introduction for this purpose, whilst other sections of the disciples of Escu- lapius indignantly protest against such an innovation, and prophesy every imaginable evil as the result of employing such methylated medicaments. It is doubtless well known to all our readers that methylated spirit, which is allowed to be sold duty free, is spirits of wine, to which a small portion of methylic alcohol, or wood naphtha, has been added. This was originally done at the recommendation of several emi nent chemists, who were engaged to report on the subject to the chairman of the Inland Revenue. Wood naphtha is very similar in chemical properties and behaviour to wine alcohol, being, in fact, the alcohol next below it in the series; it has, however, hitherto been believed to possess an odour and taste peculiar to, and inseparable from, itself. This being of a somewhat nauseous character, and the problem of separating the two bodies being at that time unsolved, the Excise autho rities felt themselves secure in permitting the untaxed sale of ordinary alcohol which had been mixed with the methyl compound; “ in fact,” write Messrs. Graham, Hofman, and Redwood, in their report on the subject, “ the more highly purified the naphtha is, with which the spirit is mixed, the more difficult will it be to effect the alteration of the mix ture, in the way contemplated, by any chemical process.” In the notices of the photographic chemicals, in the Exhibi tion, at South Kensington, we drew attention to a case of “ potable wood naphtha,” exhibited in the Eastern Annexe, and pointed out several applications for which this material would be useful in photography. In connection with the subject of employing methylated spirits in pharmacy, this specimen of wood naphtha is of considerable interest, in fact, much of the discussion could not have taken place had this purified spirit previously received the attention which it deserved. The subject is of almost equal importance to photographers as it is to druggists, and we arc, therefore, glad to be enabled to lay before our readers a few additional facts respecting this spirit. The spirit has been recently chemically examined by Mr. Harry Draper, who obtained specimens of the liquid large enough to serve for several experiments. It is reported as being colourless, its odour suggesting nothing but alcohol, and its taste but the very faintest suspicion of pyroxylic spirit. It has a specific gravity of -805. When diluted, both the scent and taste of wood spirit become more perceptible; but, so little so, that the slightest addition of an aromatic essential oil is enough to conceal them effectually ; and, it is certain, that there is no single tincture in the pharmacopoeia, which, if made with this spirit, could be distinguished from the officinal preparation by its sensible properties. This spirit was prepared under a patent taken out during the present year. Mr. Draper gives the following outline of the patentee’s method of “ treating wood, and other vegetable spirit,” pre mising that the specification offers no evidence that the patentee considered wood spirit as anything but some very impure form of ordinary alcohol, which, like that prepared from beetroot and madder, it would be desirable to render potable. Specimens of beet and madder spirit are, in fact, exhibited in the same case. The specification states that the wood spirit is first diluted with from 75 to 80 per cent, of water, allowed to repose for twenty-four hours, and then passed through a succession of filters containing coarsely-granulated wood charcoal. The only novelty claimed by the patentee is, the very ingenious arrangement of the filters, which are so placed that the spirit in the process of purification shall continually come in contact with cleaner charcoal, and that one, the first of the series, can be replaced, when foul, by a new one, not in its place, but as the last of the series. After purification, the spirit is, of course, distilled. On the small scale, and with a series of seven filters instead of fifteen, as recommended by the patentee, a spirit was obtained nearly as free from taste and smell as that exhibited at South Kensington, and there is little doubt that even this latter can be still further deodorized. Here, then, is proof positive, that the mixture containing but ten per cent, of methylic alcohol can be successfully puri fied, and that wood spirit itself, as found in commerce, can be made to so closely resemble wine alcohol, as to be when un diluted, indistinguishable from it, save to the most sensitive and tutored smell and taste. Not only is there a specimen in the Exhibition, which upsets all the calculations of our revenue chemists, but the published specification of the paten tee, details minutely the process of manufacture which can be successfully repeated by any chemist. Whilst this discovery promises to interfere somewhat with the revenue derived from wine alcohol, it has especial interest for the lover of science, in that it points to a new chemical truth. Mr. Draper says that it is impossible to avoid the conclusion, that the body which is described by chemists as methylic alcohol, plus a minute quantity of a strongly odourous hydro-carbon (pro bably the same which exists in the crude wood spirit to a large extent, which has so great an affinity for the alcohol, that not only does the ordinary process of purification by dilution with water and distillation, fail to remove it, but that the most powerful oxidising agents are equally unsuccessful. If the dilution however, be followed by an interval of repose, and the fluid be then percolated through charcoal, at a low temperature, and in such a manner that the partially purified filtrate shall not re-dissolve the separated hydro-carbon, the result is a body, which, while we can no longer attribute to it the peculiarities of taste and smell, by which methyl alcohol is now recognised, and which it is described by chemical writers as possessing, is still methyl alcohol in all its chemical characteristics and reactions. If this purified wood-naphtha can be prepared by the patentee, at a price at all approaching that of wine alcohol, it could not fail to be of great value to photographers. Its high volatility—exceeding that of alcohol, would enable a great saving to be effected in the consumption of ether, in collodion, and we cannot imagine that a collodion preparer with so pure a methylic spirit as this, would be any less sensitive a photographic agent than when made with ord nary alcohol.
