Volltext Seite (XML)
, 1862, inches it 1 accuracy, hers, anl il visitas I into the gence tM ting to te le partd f thes* mahoganr have w* ous visitor insert the t, as the/ inner the just bed generally the purity for micr, perties d nd of th iploymed generally oil is da e lamp? it be isd , and th used io • nstructe ; must be ese lamp'' f accident xclusivel isive mi- i, or W the used edbyth apouran" skert* oil,** 1 chieV juldW sratur ‘ ■ rature 4 To as re oil w insert facilitd : mint® rid tot Ine explos here?" hirty-3"2 aperatt itofp ’ higb mces, *' ile bu? 90° fa Mi ruoeg must" remai angeto" itwotlt prete cess 1 ' 1 Foo", at . ttew?" i June 13,1862.] THE PHOTOGRAPHIC NEWS. 281 rature. This is, however, beyond the limits of actual danger, and these twenty may, therefore, be looked upon as a very safe oil. The classification of these oils presents several points of interest. The whole of Young’s paraffin oils were found to be safe, whilst the whole of the oils which exploded at or below 120” were American, only two of the latter sort being considered safe. Another method of testing, which, although not quite so effectual as the above, may he of more use, as it is easier to employ, for our readers, is to try the liability of the various samples to inflame upon contact with a lighted body. This inflammability is in dose, if not in exact, relation with the explosibility. None of the samples of Young’s paraffin oil were found to take lire at 130°, whilst out of fourteen samples of American oil, eleven inflamed at this temperature, whilst three did not. It must, however, be carefully borne in mind that whenever the oils are scattered upon linen or woollen rags, at even the ordinary temperature of the air, they burst into a violent flame upon the most momentary contact with a lighted match or candle. This is the most dangerous property of the oil, and in it there is no considerable difference between the best and the worst samples of paraffin or American oils. It is generally considered that the specific gravity of an oil affords a good test of its quality, and several methods of lamination founded upon this have been frequently described in newspapers ; but O’Neill finds, however, that the specific gravity of the sample does not give any idea of its liability to explosion, but it forms a tolerably reliable means of distinguishing between the British paraffin oil and the American substitutions. Young’s oil has an average density of'833, whilst the American oils are generally below -810 ; a sample of coal naphtha, however, which was incomparably more combustible and dangerous than cither of them, had a specific gravity of ‘865. The boiling point is no better guide, for, though volatility is generally in close relation to the boiling point, the vapours of many of these oils have a diffusive power sufficient to counterbalance a very high boiling point. It is seen, therefore, that these illuminating oils are mid way between the oil-lamp oils, which cannot explode in any kind of lamp, and the very volatile and inflammable liquids such as naphtha, camphine and spirit, which are liable to explode at any time. The common coal naphtha is infinitely more dangerous, more explosive, and more inflammahle than any of the American or paraffin oils, and yet it is largely consumed as an illuminating material with but few accidents, because its dangerous properties are known and guarded against. The real danger to society Consists in selling one species of oil for another ; if paraffin Tere sold for sperm oil it would be very dangerous, genuine Pmffin oil is perfectly safe in a paraffin lamp, but a majority of the American oils are not safe in this lamp. In a recent number we gave an account of a wonderful Metallurgical feat which had just been accomplished, the fusion and casting in a mould of upwards of 2 cwt. of platinum, by M. H. Ste. Claire Deville, in the workshops of Messrs. Johnson and Malthey ; during this operation consider able quantities of fumes of osmic acid were given off, which so seriously affected M. Ste. Claire Deville, that he was obliged to return to Paris, where be has since been suffering severely. We are happy to say that he is now recovering from the ill effects of this very poisonous metallic vapour. ENLARGEMENT OF PHOTOGRAPHS* nv M. CLAUDET, F.B.S. T possibility of enlarging small photographs is at present engrossing the attention of the photographic world ; and here is no doubt that it is a considerable advantage in any respects. Small pictures are produced with the Knsatestfacility, an J with a perfection which cannot be ob- aed by large lenses and complicated apparatus. For Read at a Meeting of the London Photographic Society, June 3,1802. taking views the operator need not encumber himself with a heavy baggage, and he may carry all his appliances packed in a moderate compass. Small glass negatives are less sub ject to be injured or broken in travelling, and may be con tained in a light box. For taking portraits the prepara tion of plates is very simple and rapid, the pose is nearly instantaneous, and consequently the expression is not con strained and unnatural. Small lenses operating at a great distance from the sitter give an image without distortion and exaggeration of perspective. All is perfect in small pictures; and before an audience of experienced photogra phers I need not do more than mention the fact that if we enlarge such small pictures we can obtain portraits of great beauty, characteristic in countenance, and correct in forms. The solar camera is the means by which we are able to enlarge photographs, and if we could depend upon the sun more than it is possible in our latitude and climate, nothing would be easier than this operation ; but, unfortunately, the sun does not shine every day, and we may be sometimes waiting for his beneficial influence during many long weeks. This difficulty has induced some persons to replace the light of the sun by artificial light, and the electric light has been tried with some success; but this is a very difficult and expensive process, which very few operators could practically employ. During the months preceding the reception of photo graphs at the International Exhibition, wishing to prepare enlarged photographs for my contribution, I was constantly watching for the appearance of the sun ; and I may say that during five months I hardly saw it more than ten or twelve days. Still I have been able to produce all the specimens which have been admitted at the International Exhibition ; they are all from negatives of cartes de visite, enlarged seven or eight times, and I hope the result will prove what can be expected from the solar camera during the clear days of the fine season. The enlargement of negatives, however, has some limits, when we wish to produce Black photographs. I think that an enlargement of six to eight times is the greatest propor tion which ought to be employed. But if you wish to en large cartes de visile to the size of nature, the small defects imperceptible in the negative are magnified to a degree so apparent that the picture requires considerable touchings up and correcting, in order to give to the picture the appearance of a perfect and clean drawing worthy of being framed. These corrections, however, can be made without altering the character of the photograph, which has all the qualities of the small carte de visite, preserving proportions of all the forms, and the natural expression of countenance. The re sult is far preferable to all the attempts made for producing at once large portraits with lenses of considerable aperture, which require a long sitting, distort the proportion of the figure, and, if the model has not moved, exhibit the forced expression of a sitting too much prolonged. Although, as photographs, many parts of the figure which may be in the right focus require very little touching up, still the greatest part is so ill-defined and so much out of proportion, that it is absolutely necessary to modify them considerably. The touchings of enlarged photographs, at all events, can be done without altering any proportions; and when these pictures are destined to be painted or coloured, they are even in a better condition for the artist than more strongly marked photographs taken direct in a large size. Large photographic portraits are, in general, not very agreeable in effect, and, to please the public, they require colour. The more perfect the photograph is, and the more it shows all the defects of the face. It is not very desirable to exhibit all the roughness and every wrinkle of the skin in black lines. For this reason some artists, not under standing the impossibility of imparting the same degree of softness to the whole picture by it, have recommended to operate a little out of focus. Certainly, if all the parts of the picture had the same focus it would be of some advan tage, for the artistic effect, to obtain an image in which every