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160 [April 4, 1862 THE PHOTOGRAPHIC NEWS. one being a double salt of nitrite of ammonia and oxide of copper. To obtain this in large quantities, the blue liquid is to be evaporated to dryness on a water bath, the residue pulverised, and submitted to the action of boiling alcoholic ammonia. The filtered liquid on cooling deposits the salt in the form of needle-like prisms of a beautiful violet blue colour. This salt has a somewhat remarkable composition, containing NO.CuO.NH,O.HO. A small quantity of the compound wrapped in paper and placed on a steel anvil, detonates when struck with a hammer. It dissolves in contact with a little water, producing intense cold, and yielding a solution which possessses the curious solvent property on cellulose, &c., which is under discussion. In his investigation on this compound, M. Peligot suc ceeded in discovering a new blue pigment of great beauty. The fine turquoise-blue precipitate, which is thrown down when a soluble salt of copper is decomposed by an excess of caustic potash, or soda, has often been regarded with admi ration by artists ; but unfortunately, chemists have not been able to prepare this body in a permanent form. It is a hydrated oxide of copper, CuO.HO, but it loses water almost immediately, and turns black even whilst it is being washed in cold water. When, however, the above-named nitrite of copper and ammonia is dissolved in a very small quantity of water, and then the solution greatly diluted, a similar turquoise-blue precipitate is obtained, having the same composition as the ordinary precipitated hydrated oxide, but possessing the property of resisting the action of boiling water, and able to bear a temperature of 212° with out injury. This new blue hydrated oxide of copper, which may be ranked as a new and useful acquisition to science and the arts, absorbs atmospheric carbonic acid slowly, and without changing colour. It is a very finely divided crys talline precipitate, and its beautiful colour will doubtless before long render it useful in painting, and for printing colouied stuffs and paper. If this hydrate could only be produced under the above circumstances, its industrial uses would of course be very limited. But while studying its properties, the discoverer found several methods of preparing it from all the salts of copper soluble in water; particularly from sulphate of copper. It can in fact be obtained by treating with an alkali a salt of copper dissolved in water, to which a slight excess of ammonia has been previously mixed; also by pouring caustic potash or soda into a salt of copper mixed with an ammoniacal salt; or by adding a quantity of water to a slightly ammoniacal solution of nitrite of copper. Thus the expense of preparing this colouring matter is no obstacle. It must not be confounded with the article known as “ English blue ash,” this consists of carbonate of copper, the tint of which, though rather darker, is generally less pure than that of the hydrated oxide of copper. To the photographer, however, this stable oxide of copper possesses other advantages, besides its capability of being employed as a pigment. By simply dissolving it in am monia a liquid is obtained which is decidedly the best sol vent for cellulose, and the other substances more or less soluble in Schweitzer’s reagent. Concentrated ammonia dis solves from 7 to 8 per cent, of the hydrate, the solution having the deep blue colour common to all salts of copper in contact with excess of ammonia. From the ease of its preparation and the many theoretical advantages which would be derived from employing pure cellulose or silk as the medium for photographic pictures, in preference to the nitro-compound, gun-cotton, there is little doubt that this solution would well repay any experimentalist for the time and trouble which he might devote to the subject. One of the advantages which this solution possesses over the old solvent formerly used is that the dissolved substance can be precipitated without alteration by the • addition of an acid; whilst by operating under the same circumstances with the blue liquor, resulting from the action of air and ammonia on copper, the nitrous acid which becomes free, acts more or radiated with a file or still better For the same reason, the polish is ini. , ; , of the substance ; thus a plate of brass is more brillian' less energetically on the organic substances contained in! solution. It is, moreover, from the presence of this o® which is found in the liquid in simple solution in ammo, that the liquid obtained by the direct action of air and® monia on copper, derives the property of dissolving 0 lose; for by placing this substance in contact with ni" of copper and pure ammonia dissolved beforehand in al water, it neither gelatinises nor disappears, as happens, we employ ether on ammoniacal solution of this oxida copper, or the liquid named at the commencement of" article. Soon after these solvents were first made known to 2 photographers of this country in the pages of the Pz graphic News, we chronicled a few attempts which J been made to employ them in photography. From # results and others which have since come to our knowlei there can be little doubt that were the difficulties incid. to the first introduction of a new substance overcome, cupreus solution of cellulose and silk would prove a ’ useful agent in the photographers’ laboratory. Possibl might never be found to have advantages which " enable it to compete with collodion, but there are several J 1 directions in which such a solution of so ordinarily inso” a material would be of the greatest value. Some of ’ applications are at present under trial, and will foru subject of another article. Others will doubtless so? themselves to any one who experiments upon the sul Our object at present is to draw the attention of es menters to this neglected branch of the art, and to ip' them to take up so promising a field for investigation. certain limit. Itriated surfaces send more light in the direction®; stri;e than perpendicularly, for in this direction shads produced. We may observe it upon a plate of whit® radiated with a file or still better with plates of pearl. Auenced by the D J 1 -i1:ontV APPLICATION OF PHOTOGRAPHY* dove’s new photometric process. In the experiment with the Newton's coloured circa cannot obtain the intensity of a white disc, but only resulting from the absorption of colour in particular, may be satisfied that there is absorption with the col circle, by directing the photometer upon the turningd and varying the inclination until there is competd then on turning the circle to view the white surfad"o the same inclination. To measure the absorption ’ g suffice to place a black sector upon the white surfa® gradually augment the dimensions. If we divide a disc into 10 sections, alternately whit; black, the quantity of light it sends to the eye in to” will be the same as if it were divided into 50 sections’ nately white and black. But in the first case each B, acts upon the eye five times longer than in the second and this must exercise some influence upon our apprec of the lighting. ToM. Dove it always seemed that bril increased in this case until the velocity had attai® a plate of copper. To measure the lighting power of luminous source, difficulty, as is well known, is to have an invariable V constant term of comparison ; wo employ an Argano y a gas burner of known diameter, discharging gas Un constant pressure or rather of a platinum wire redder a current of determined intensity ; but there is alway uncertainty between one experiment and another. i We place the horizontal microscope in positiolpe direct it alternately towards the two lights, the distje which must be varied until the photographic proo ", in front by the constant light, disappears. We P 0 two lights to be tested in the prolongation of thea * Concluded from p. 149. Ar micro the li ; hyai tested This । time, Inthi moon wire i or th comp they that list: suffi this the of th the t eye-] nean phot the < covei scop< same that silve incic that more cove T) mirr M.I of tl nuti as a Atme tage F the rapi by1 sam are exp con ini ap wh th an act col the wh mi gla of i col cor tio pri 1)1 It of
