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MA [March 28, 1862. 148 THE PHOTOGRAPHIC NEWS. 0 mod above. cm; lights t0 ilphide is ot consi- ■How colour, and its measured. APPLICATION OF PHOTOGRAPHY. dove’s new photometric process. >ster Ge of I 6 fact dark ground. From this it is evident, that the lines disappear when the light falling from above, and coming from below, are both of the same degree of integ In new microscopes, the illuminating mirror can to move laterally by a double angular move besides, the instrument can be made to pass fv tical position through every degree of inclination 1 frol the diameter of which diminishes as they proceed I j object bearer, and these diameters must be ac oxy-sulphides. These are of yellow or orange colours, and are sometimes, but rarely, used as pigments. Antimony also forms compounds with both sulphur and oxygen, called 2nd. We me which, graphi 3rd. incline represe horizor paralic to the i To n sufticie micros horizo examii The sa incidet Under■ Ifth To this Jeplace the hor 'ays be the Jeni M.D '■mt, te k their by diffu Placing >tc >late .Na Ntii p ^aWixl, "g2k 6ningi "Pon a' Dation, I Sun One fact connected with these bodies may, however, be worth remembering, and that is that most of the sulphur of commerce contains arsenic, in the form of per-sulphide. Arsenious acid may be fused with any excess whatever of sulphur; sulphurous acid is evolved, and a brownish yellow sulphide of arsenic formed, which, on cooling after fusion, remains soft for a long time; its powder is yellow, the brightness of the colour increasing with the quantity of arsenic. On distilling a compound of this nature, sulphur passes over, accompanied by a continually increasing quan tity of arsenic, much of the ordinary sulphur of commerce is really a compound of this nature. The sulphides of arsenic are of considerable value as pig ments, owing to the brilliancy of their colour and their inalterability under unfavourable atmospheric agencies; being already saturated with sulphur, sulphuretted hydrogen can have no further action on them. Sulphides of Antimony.—Like arsenic, antimony forms several compounds with sulphur, the principal being the ter- and the penta-sulphide. The ter-sulphide of antimony exists in two distinct modifications, the crystallized, and amorphous condition. The first is of a leaden grey colour and is the common ore antimony, it possesses but little special interest. We may, however, mention that it is used in some photogenic compositions to replace sulphide of arsenic; a good white fire may thus be made by mixing together 7 parts of nitre, 2 parts of sulphur, 1 part of the native grey sulphide of antimony, and 1 part of red lead. Amorphous Tersulphide of Antimony, known also by the name of mineral kermes, is prepared on the large scale from the grey sulphide by a tedious process of solution in caustic or carbonated alkali, and precipitation. It is of a red colour, and is used in medicine, and also as a pigment. Penta-sulphide of Antimony.—This is of a bright yellow colour, and is prepared on the large scale in several ways : cither by precipitating antimonic acid in solution by sul phuretted hydrogen, or by boiling the grey sulphide with caustic alkali, and sulphur, and then precipitating by an acid. horizontal. . y To weaken the light we can employ the following ’ 1st. Diminish the aperture of the object bearer. ) end we take a small rule, a slide pierced with circu- again see the lines disappear. Starting from this posil the least rotary movement of the eye-piece causes the ° lines which had appeared before as black, to reappeb -IrK white, which is a proof of the sensitiveness of the es" of deteP ment. We also recognise that, if everything being ip * position where the figures disappear, we interpose in. path of the light coming from below, a plate of glass slisz ground on the surface, the figures immediately appear upon a dark ground, while the contrary takes place n plate of glass is placed in the path of the light coming Further allusions to them is unnecessary. Sulphide of Zinc is produced by acting on a soluble com pound of zinc with a weak acid, by sulphuretted hydrogen; a white powder is precipitated, which is the sulphide of zinc. When heated it loses combined water, and becomes of a pale yellowish colour. This compound is formed when zinc- white is exposed to an atmosphere which is contaminated with sulphuretted hydrogen. Being of the same colour as the original pigment this gas has no apparent effect on it; hence the advantage of using zinc-white, instead of white lead in painting: the latter body, as is but too well known, readily tarnishing in a sulphuretted atmosphere to a brown surface, owing to the dark colour of its sulphide. Sulphide of zinc is found native in transparent pale yellow crystals. It then goes by the name of blende. Sulphide of Cadmium,—This is one of the most important of the metallic sulphides. It is formed by igniting oxide of cadmium with sulphur, or by precipitating a solution of a cadmium salt with sulphuretted hydrogen, or an alkaline sulphide. It is also found native. The native sulphide is of a honey yellow colour, semi-transparent when in mass, and yields an orange yellow or brick red powder, which becomes carmine red when it is heated. The artificial sul phide in the precipitated state is an orange yellow powder, which when heated to redness becomes first brownish, and then carmine red. As a pigment this sulphide is of consi derable value, owing to its brilliant yel ’ , 2 entire permanency in an impure atmosphere. It is usually prepared by precipitation, and its colour may be slightly varied by alterations of temperature, and employing solu tions of different strengths, as well as by certain subsequent treatment which the sulphide undergoes. These details are avove. To compare the lights, it is evident that if the me employed which necessitate a weakening of the more 1# lights to give it an equality with the feeblest, contay ) Till exact means of measuring the degree of weakening, We f TE be able to arrive at the relation of intensities under I EN same conditions. mostly trade secrets, each manufacturer employing a slightl! different process which experience has taught him to " best. J Bisulphide of Tin.—The only compound of tin and sulph which is of interest to the photographer is the bisulphide^ tin, known also under the name of aurum musivum, or most* gold. It is prepared in several ways, one of the most sue cessful being to mix together 5 parts of protosulphide 11 tin, and 8 parts of corrosive sublimate. The mixture bew! placed in a loosely closed flask, and heated in a sand bath A gentle heat is applied for some hours, and afterwards th heat is raised, but not quite to redness. The greater part 1 ’ the mosaic gold is found at the bottom of the vessel; th smaller but purer and finer portion sublimes to the upP part of the flask. It forms gold coloured, translucedl delicate scales, or six-sided lamina?, unctuous to the toad It is largely used in the fine arts : it does not tarnish in 0 air. C0rners. a thic Che grea Ce aper A new photometric process is proposed by Professor Dot It is extremely sensitive, and may be applied to obj which are strongly or feebly luminous, uniformly or 11 equally coloured, transparent or opaque. It enables the * perimentalist to measure the luminous power of opti instruments, and moreover it possesses the advantage of! 1 • quiring the use only of a microscope, an instrument in ’ berror, possession of every physicist and naturalist. . narer, 1 It is well known that there are certain objects, such 1 instance as the epidermis of the ephemera, which viewed the microscope appear dark upon a light ground whent or rather, have a certain determinate relation of intend vi" “ each other when they fell under different angles. , wi _ Nichols’ polarizing prism be fixed upon the object b 1an ePa and if the ordinary eye-piece be replaced by a Niy nn3P-b “ analysing prism, on turning the lathe properly, we 8 Bt/far ev again see the lines disavvear. Starting from th nosib n Aces can be"' vement, , >of from tb te; ., It wi 5 late are lighted from beneath, but are, on the contrary, light a dark ground when wo cover up the mirror. This is es ca *- cially the case with micro-photographs. Upon lighjtiL 4PP them from below, they show black lines upon a white grotl m’ when the mirror is covered they appear in white lines e C