134 Scientific Intelligence. 



chlorine may be facilitated in an extraordinary degree by dissolving 

 iodine in the body to be acted on, and then passing chlorine directly into 

 the solution. In this manner benzol yields the fluid compounds CjaHj 

 CI, Ciall^Clj and CjaHgCla, chlorhydric acid being evolved. Benzoic 

 acid dissolved in chloroform is easily attacked by chlorine; bisulphid 

 of carbon, containing iodine in solution, is decomposed by chlorine at a 

 gentle heat, yielding chlorid of sulphur and chlorid of carbon. Large 

 quantities of chloracetic acid may be prepared in a similar manner, even 



simply as a condenser of chlorine, and compares the reaction with that 

 of the super-chlorids of phosphorus and antimony. — Zeitschrift fur 

 Chemie und Pharmacie, 1862, p. 99. w. Q. 



1 1. The Tannin Process ; by Prof. Edwin Emerson', Troy. — Photogra- 

 phy on dry plates possesses so many advantages over the wet processes for 

 outdoor work, that great^ attention has been given by scientific photogra- 

 department V 



processes a 



entirely new method which should not be subject to the defects 



the old methods, or so to improve some one of the 1 



render it more easy and certain in the practical 



amount of laborious research which has been made to this end, can only 



be appreciated by those who are femiiiar with the practice of Photography 



in its different branches. 



Among the dry processes, the Collodio- Albumen and the FotherglU 

 have, until very recentlv, received the most attention, and in the hands of 

 adepts have given excellent results. But as success in these methods 

 depends greatly upon, the mechanical state of the collodion, and the 

 favorable condition of the sensitizing bath, it is evident that neither of 

 them can be worked with certainty by the generality of operators. 



Major C. Russell, of England, after a series of experiments extending 

 through five or six years, has peifected a dry process, now known as tht 

 Tannin Process. Its advantages may be briefly summed up as follows :— 

 1. It is simple. 2. It is not dependent upon the mechanical state of tha 

 collodion. 3. A sensitizing bath in ordinary working condition is suffi- 

 cient. 4. The development of the latent image is under compl^j^te control. 

 5. It gives, if desired, great intensity. 6. It affords an excellent tone. 

 T. The prepared plates will keep well both before and after exposure. 

 8. The silver, in the development is thrown down in a very finely divided 

 state, and it is thus more favorable for obtaining extreme sharpness. 



As might have been expected this process has excited great interest m 

 the photographic world. Many experiments have been made upon it, and 

 thus far the testimony has been uniformly in its favor. Our own obser- 

 vations have extended through a year and experience corroborates fully 

 the favorable estimate which has been formed of it by others. 



We give now the details of this process as worked by us : — The pla*^ 

 should be very carefully cleaned, and must be perfectly dry before coating 

 with collodion; it is coated and sensitized in the same manner as for the 

 wet process; it is then washed thoroughly in pure water, with five or siX 

 changes of water; a good plan is to have a succession of baths of pure 



