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The photographic news
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- 27.1883
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The photographic news
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Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
- Ausgabe No. 1270, January 5, 1883 1
- Ausgabe No. 1271, January 12, 1883 17
- Ausgabe No. 1272, January 19, 1883 33
- Ausgabe No. 1273, January 26, 1883 49
- Ausgabe No. 1274, February 2, 1883 65
- Ausgabe No. 1275, February 9, 1883 81
- Ausgabe No. 1276, February 16, 1883 97
- Ausgabe No. 1277, February 23, 1883 113
- Ausgabe No. 1278, March 2, 1883 129
- Ausgabe No. 1279, March 9, 1883 145
- Ausgabe No. 1280, March 16, 1883 161
- Ausgabe No. 1281, March 22, 1883 177
- Ausgabe No. 1282, March 30, 1883 193
- Ausgabe No. 1283, April 6, 1883 209
- Ausgabe No. 1284, April 13, 1883 225
- Ausgabe No. 1285, April 20, 1883 241
- Ausgabe No. 1286, April 27, 1883 257
- Ausgabe No. 1287, May 4, 1883 273
- Ausgabe No. 1288, May 11, 1883 289
- Ausgabe No. 1289, May 18, 1883 305
- Ausgabe No. 1290, May 25, 1883 321
- Ausgabe No. 1291, June 1, 1883 337
- Ausgabe No. 1292, June 8, 1883 353
- Ausgabe No. 1293, June 15, 1883 369
- Ausgabe No. 1294, June 22, 1883 385
- Ausgabe No. 1295, June 29, 1883 401
- Ausgabe No. 1296, July 6, 1883 417
- Ausgabe No. 1297, July 13, 1883 433
- Ausgabe No. 1298, July 20, 1883 449
- Ausgabe No. 1299, July 27, 1883 465
- Ausgabe No. 1300, August 3, 1883 481
- Ausgabe No. 1301, August 10, 1883 497
- Ausgabe No. 1302, August 17, 1883 513
- Ausgabe No. 1303, August 24, 1883 529
- Ausgabe No. 1304, August 31, 1883 545
- Ausgabe No. 1305, September 7, 1883 561
- Ausgabe No. 1306, September 14, 1883 577
- Ausgabe No. 1307, September 21, 1883 593
- Ausgabe No. 1308, September 28, 1883 609
- Ausgabe No. 1309, October 5, 1883 625
- Ausgabe No. 1310, October 12, 1883 641
- Ausgabe No. 1311, October 19, 1883 657
- Ausgabe No. 1312, October 26, 1883 673
- Ausgabe No. 1313, November 2, 1883 689
- Ausgabe No. 1314, November 9, 1883 705
- Ausgabe No. 1315, November 16, 1883 721
- Ausgabe No. 1316, November 23, 1883 737
- Ausgabe No. 1317, November 30, 1883 753
- Ausgabe No. 1318, December 7, 1883 769
- Ausgabe No. 1319, December 14, 1883 785
- Ausgabe No. 1320, December 21, 1883 801
- Ausgabe No. 1321, December 28, 1883 817
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44 THE PHOTOGRAPHIC NEWS. [JANTARY 19, 1883. To sum up, I have found that emulsions prepared with a distinct trace of acid during the boiling seem less subject to green fog than emulsions perfectly neutral, and the latter less subject to green fog than emulsions at all, if only slightly, alkaline. Moreover, emulsions prepared with a slight trace of free bromine or iodine seem less prone to green fog than emulsions containing no free halogen. It would appear probable, therefore, that at least one of the causes of green fog is the formation of a small quantity of some compound of silver and gelatine, and aggravation of its fogging properties by boiling, this compound not being decomposable by the salts of the halogens, but decomposable by the halogens themselves. I am speaking now of green fog occurring under ordinary circumstances. And now for a few experiments relative to the circumstances under which green fog appears on development. I need scarcely refer to its well-known tendency to appear with pyro-develop- ment, nor to the fact that it is especially liable to come up on forcing with ammonia ; but it may be new to some, that it may be obtained with ferrous oxalate development, but only under certain circumstances. Some time since, I found, and pointed out to Captain Abney, that plates liable to green fog showed green fog with iron developer prepared with ammonic oxalate. The developer was slightly alkaline (with ammonia), and, when rendered acid with oxalic acid, no green fog appeared. Now, to ordinary iron developer prepared with potassium oxalate and ferrous oxalate you may add just a slight trace of ammonia without precipitating oxide of iron. A developer so treated will bring up green fog. If ammonic carbonate be added to the iron developer, green fog is not produced; but a yet further amount of ammonia may then be added, and developer so treated is the most powerful producer of green fog that I know of. Here is a plate placed for a short time in such developer without having been exposed ; part of it is not fixed, but the fixed part is so dense that I have but little doubt that, if it had been left in the developer sufficiently long, there would have been nothing left to fix out. The appearance of green fog on a plate, therefore, is plainly due to the action of free ammonia together with an agent capable of reducing a sub-haloid of silver. If the iron developer be made slightly alkaline with potash or soda, grey fog is produced on plates liable to green fog. If fog is produced when the developer is acid, it is doubtless due to some other cause. It has frequently been stated that sulphite of soda is a producer of green fog. The capability of getting green fog with iron developer gave me a good opportunity of testing this state ment. Sulphite of soda was mixed in considerable quantity with iron developer, but no green fog resulted when a plate was immersed in it. Another plate was immersed in ammonia and sulphite for forty-five minutes with no result. I am inclined, therefore, to think that sulphite of soda does not tend to produce green fog, excepting by the slightly longer time required to develop a plate when it is present. I may mention, also, that I immersed a plate prone to green fog in a very weak solution of iodine in alcohol: the only result was, that the part immersed was slower considerably, green fog being equally prominent over the plate ; showing that though iodine might check the evil in course of preparation, it was in capable of curing it afterwards. I have also tried immersing a plate in bichromate of potash, as has been suggested ; but green fog was only slightly, if at all, reduced. By the way, every one who has had any experience of green fog must have noticed that it appears strongest on parts not acted upon by light. I have seen no specimens in which such has not been the case. If a plate subject to green fog have only one half of it slightly exposed to white light, and then be exposed and developed in the ordinary way, the part acted on by light shows little or no signs of green fog, if the first exposure be suitably timed, but a slight veil is apparent. Probably, if plates subject to green fog under ordinary circumstances were first exposed to light, and then treated with bichromate of potash or chloride of copper, their tendency to fog might be stopped. In connection with this subject I have made use of the phrase, “ under ordinary circumstances.” What I mean by this will appear from the following. Captain Abney told me, a short time since, that he could produce green fog on any plate if he left it in the developer long enough. I thought that, if that is the case with alkaline developer, I could do the same, only much more so, with iron developer and ammonia. Here is a plate not liable to green fog under ordinary circumstances, that has been so treated, and you will see that it possesses a dense ruby tint, and might be used for a dark-room window. LOCKYER’S DISSOCIATION-THEORY. BY DR H. W. VOGEL.* In February, 1880, I took occasion, on the ground of my observations to the spectrum of chemically pure hydrogen, to take objection to Lockyer’s view that calcium, at a very high temperature, is dissociated. From the fact, inter alia, that of the two calcium lines, H' and H", only the first is present in the spectra of so-called white stars photographed by Huggins, Lockyer proceeded to lay down the theory that calcium at a high temperature is decomposed into two substances, X and Y, of which the first gives the line H", the other the line H", and that in the stars referred to, only the first is met with. Against this I urged that hydrogen, besides the four known and easily visible lines, has a remarkable line of very intense photographic power, which nearly coincides with Fraunhofer’s H‘, and that one is the more warranted in regarding the supposed calcium- line observed by Huggins as a fifth hydrogen line, that the hydrogen lines in the spectra of those stars are developed in a striking manner, and also the ultra-violet star lines observed by Huggins agree with the ultra-violet hydrogen lines photo graphically fixed by me. Lockyer, however, has not given up his idea of dissociation, but sought new proofs of it by the spectroscopic method. He calls attention to the fact, inter alia, that in the spectrum of sun-spots, certain iron lines appear broadened, and others not; that, moreover, many of them, as A 4918 4 4919’7 do not occur in the spectrum of protuberances, show other iron lines, but do in the spectrum of spots ; that in the latter, again, the iron-lines are occasionally absent, which the former contain, and he proceeds to say : “ there is, accordingly, no iron in the sun, but only its constituents.” This argumentation Liveing and Dewar have already opposed, having proved that certain spectral lines of a substance, e.g. 5210 magnesium, and various calcium-lines, are only visible when certain foreign matters are present—in this case hydrogen on the one hand, and iron on the other ; that accordingly the absence of certain iron lines in the spectra of the spots or pro tuberances may not be attributed to a dissociation, but to the absence of foreign matters which occasion the appearance of these lines in force. Lockyer now takes his stand, however, on another fact, which is not explained by Liveing and Dewar’s experiments, and which certainly seems to afford a firmer basis for his theory of dissocia tion than the facts referred to above. He says : “ The last series of observations relates to the degree of motion of vapours in the sun-spots, which it is known, is indicated by changes in the refrangibility of lines. If all lines of iron in a spot were produced by iron vapour, which moves with a velocity of 40 km. in a second, this velocity would be indicated by a change of the refrangibility of all lines. But we find that that is not the case. We find not only different motions, which are indicated by different lines, but observe in the degree of motion the same inversions as in the breadth of the lines. This fact is easily explained if we suppose dissociation, and I know no more simple way of explaining it.” Lockyer cites as an example that in the spots of December 24, 1880, and January 1 and 6, 1881, a certain number of iron lines appeared bent, while others remained straight. Now I believe it is possible to explain these facts on the basis of numerous observations in spectral analysis of absorption with out needing to have recourse to the hypothesis of dissociation. It is known that the position of the absorption-band of a substance depends very essentially on the dispersion of the medium in which it is dissolved or incorporated. One often observes that in strongly dispersive media the absorption-bands of a substance are displaced towards the red. Now, the remark able case often here occurs that certain absorption-bands are displaced with the increase of dispersion of the solvent, while others are not. Thus Hagenoach observed that, e.g., the chlorophyll bands I. III. and IV. lie more towards red in alcoholic than in etheric solution, while the band II. in both solutions shows exactly the same position. I observed similar cases with uranian protoxide salts and with cobalt compounds. Now Kundt has already called attention to the fact that for absorption-spectra of gases the same rule holds good as for the absorption spectra of liquid substances. He adds, indeed : “It is only questionable whether, if, e.g., hyponitrate gas be mixed with various other transparent gases, the displacements of the * A paper by Herr Hermann W. Vogel, read to the Berlin Academy on November 2,1S82. Communicated by the author.
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