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NovEMBER 16, 1883. | THE PHOTOGRAPHIC NEWS. PHOTO-LITHOGRAPHY AND PHOTO ZINCOGRAPHY. BY MAJOR J. WATERHOUSE, B.S.C., Assistant Surceyor-General of India. Chap. XIII.—Asphalt Processes—(continued). Dr. Kayser also gives the results of spectroscopic obser vations of solutions of different asphalts, and their com ponents, the solutions being made in chloroform, an d of as nearly as possible the same intensity of colour. These results are rather interesting, as will be seen from the accompanying diagrams, copied from Dr. Kayser. G F EyaD CB F EyaD CB Bechelbronn Asphaltum. Asphaltene trom ditto. Component of ditto, soluble in Ether. Trinidad Asphaltum. Component of Syrian Asphaltum soluble in Alcohol. Coal Tar Asphalt. Ditto ditto insoluble in Ether. Syiian Asphaltum. Component of ditto, soluble in Alcohol. Petrolcnc from Bechelbronn Asphaltum. Ditto ditto insoluble in Ether. itto ditto soluble in Ether. Specially characteristic of the Syrian and Trinidad asphaltums are the three absorption bands a B 7, between the lines D and E, which, however, are entirely due to their components soluble in ether and alcohol, because a solution of the portion insoluble in those solvents does not show them. The difference between the components soluble in alcohol and ether respectively is. that the first shows a very strong band at 7, which is wanting in the latter; while in the latter, B is much stronger. Bechelbronn and coal-tar asphalts do not show these bands. Dr. Kayser considers these spectroscopic appearances of practical importance as affording a means of distinguishing natural from artificial asphalts, and of ascertaining from the entire disappearance of the bands when the exhaustion with ether is complete, and only the most sensitive body remains. The writer finds, however, that though the bands are much stronger in some specimens than in others, they are not very easily distinguishable; and the method, therefore, is not likely to be of much practical use. Dr. Kayser says nothing regarding the sensitiveness of asphaltum to the solar spectrum ; but Dr. J. W. Draper (Scientific Memoirs, p. 408) found that it is sensitive to the whole range of the spectrum from below A ; in the red to below H ; in the violet, every ray acting and giving a con tinuous proof, except where the Fraunhofer lines fall. He used solutions of West India bitumen in benzole, so thin as to leave an iridescent coating on a glass plate. The exposure given was about five minutes, and the plate was developed with a mixture of benzine and alcohol. Dr. Draper says that bitumen is more sensitive than is generally supposed, and properly used he considers it scarcely inferior to chloride of silver. Apart, however, from the natural sensitiveness of any particular specimen of asphaltum, its sensitiveness depends practically upon the thickness of film necessary to effect the object in view. An exceedingly thin film which might answer perfectly for scientific observations would be found much more sensitive than the thicker films required for resisting acid in the etching processes. The writer has found that chlorine and iodine exert a marked influence on asphaltum, rendering it insoluble and more sensitive to light. By coating a silvered copper plate with a solution of asphaltum in turpentine to which a little iodine has been added, aud exposing it to light, a visible image is obtained, which may be made quite permanent by fixing with hyposulphite of soda after the development with turpentine. It is possible that this combination of the processes of Niepce and Daguerre might be useful for camera pictures to be afterwards etched or engraved; but the writer has not yet tried this. Capt. Biny, of the French Engineers, has found that coal-tar, as well as the light oil and solid pitch obtained from it, contains a substance which is very sensitive to light, and well adapted for producing pictures in half-tones on paper or metal. The hard pitch contains the most of this substance, and a solution of it in benzole forms the sensitizing solution, which will keep a long time in good order, though before use it should be filtered in order to remove the clotty particles which form in course of time in the fluid and on the sides of the bottle. Paper coated with this solution gives a visible image on exposure to light, and after development with benzine gives a much finer and less granular image than asphaltum. Plates or paper coated with it lose their sensitiveness if exposed to heat in drying. The above is a resume of the latest contributions to the chemistry of asphaltum and its congeners, as far as they are of interest to photographers ; but there are still many points requiring investigation. As will be seen, the results obtained by different workers and observers are most con - tradictory. It is to be hoped that the renewed attention now being given to these asphaltum processes will result in a better knowledge of this very variable substance. In our next we shall enter upon the practical details of these processes. Addendum to Chapter XIII. (Asphalt Processes. I.) Since writing the above chapter, the writer has met with a curious experience which seems worthy of record as coroborating Bayer's observation that a thin coating of bitumen is not affected by light under a collodion film gummed down upon it, even though the latter be perfectly transparent. It does not, however, seem to support the theory which Bayer deduced therefrom, that this effect was due to deprivation of oxygen. A copper plate coated with Husnik’s solution of