Orr's Circle of the Sciences: Practical chemistry

W.S. Orr and Company, 1856

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Seite 121 - OPTICS. light, and let it be so arranged, that as the beam of light descends towards the floor, it just passes over the top of the side of the vessel next the window, and strikes the bottom on the side farthest from the window. Let the spot where it falls be marked. Now, on filling the vessel with , water, the ray, instead of striking the original spot, will fall considerably nearer the side towards the window. And if we add a quantity of salt to the vessel of water, so as to form a dense solution,...
Seite 102 - The images formed by means of a camera obscura have been found to be too faint to produce, in any moderate time, an effect upon the nitrate of silver.
Seite 102 - The copy of a painting or the profile, immediately after being taken, must be kept in an obscure place ; it may, indeed, be examined in the shade, but in this case the exposure should be only for a few minutes ; by the Light of candles or lamps, as commonly employed, it is not sensibly affected.
Seite 277 - By slightly colouring tho plate with the chloro-iodide, and then exposing it for a proper time over the bromide, proofs may be obtained in a fraction of a second, even late in the afternoon. A yellow...
Seite 105 - In conducting this operation, it will' be found that the results are sometimes more and sometimes less satisfactory, in consequence of small and accidental variations in the proportions employed. It happens sometimes that the chloride of silver is disposed to darken of itself, without any exposure to Light : this shows that the attempt to give it sensibility has been carried too far. The object is to approach to this condition as near as possible, without reaching it, so that the substance may be...
Seite 121 - ... considerably nearer the side towards the window. And if we add a quantity of salt to the vessel of water, so as to form a dense solution, the point where the ray strikes the bottom will move still nearer to the window. In like manner, if we draw off the salt water, and supply its place with alcohol, the beam of light will be still more highly refracted ; and oil will refract yet more than alcohol.
Seite 276 - ... enterprising operator, who last year made a tour on the continent, and brought home some of the finest proofs I have ever seen, entirely failed this season in obtaining clear and perfect pictures, from the constant appearance of a mist or cloud over the prepared surface. This appears to be caused by the deposition of moisture upon the plate, arising from the water in which the bromine is dissolved. To obviate this, some have recommended the pan to be kept at a low temperature in a freezing mixture;...
Seite 121 - If the medium which the rays enter be denser, they move through it in a direction nearer to the perpendicular drawn to its surface. On the contrary, when light passes out of a denser into a rarer medium, it moves in a direction farther from the perpendicular. This refraction is greater or less ; that is, the rays are more or less bent, or turned aside, from their course, as the second medium, through which they pass, is more or less dense than the first. To prove this in a satisfactory way, take...
Seite 459 - Parliament is a sperm candle of six to the pound, burning at the rate of 120 grains per hour.
Seite 102 - They have been covered with a thin coating of fine varnish, but this has not destroyed their susceptibility of becoming coloured; and even after repeated washings, sufficient of the active part of the saline matter will still adhere to the white parts of the leather or paper, to cause them to become dark when exposed to the rays of the sun.

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