M. TECHNOLOGY. 475 



M. TECHNOLOGY. 



KECENT PROGRESS IX PHOTOGRAPHY. 



The success attending recent experiments in photography 

 seems to justify the expectation of an early revolution in the 

 manipulations of some of its fundamental processes. In the 

 negative process, all the more vexatious and uncertain details 

 have been in a great measure eliminated, and the practice of 

 this branch of photography has been adapted to even the or- 

 dinary tourist. The collodion negative process, which dis- 

 placed the daguerreotype process, about twenty-five years 

 ago, as much by reason of its wider range of applications as 

 because of its comparative simplicity and certainty, has re- 

 mained essentially the same as when first introduced. Im- 

 provements in it have been mainly in the detail, and their ad- 

 justment to the various applications of which it was soon 

 found susceptible. Its inconveniences, and the apparently 

 needless complexity of its manipulations, were soon felt, and 

 attempts made to remedy them; but the sensitive collodion 

 film is still produced upon the glass plate by the professional 

 photographer by charging it indirectly with the iodide and 

 bromide of silver, sensitive to light. Some soluble iodides 

 and bromides, insensitive to light, are first introduced into 

 the collodion ; and after a film of it has been formed upon 

 the glass, it is rendered sensitive by immersing it in a solu- 

 tion of silver nitrate, where the insoluble haloid salts of sil- 

 ver form in the film, while the nitrates of the other bases, 

 previously combined with the halogens, remain in the solu- 

 tion. But besides the complexity of the manipulations, the 

 silver solution is expensive and voluminous, and requires ex- 

 pensive and fragile receptacles ; and, withal, has generally 

 been regarded as the most decided variable in the process, 

 and, directly or indirectly, chargeable with most of its fail- 

 ures. In out-door photography, all the inconveniences and 

 uncertainties attending the use of this solution are multiplied 

 to such an extent that, failing in attempts to eliminate it alto- 

 gether, the best effort, especially of amateurs, was directed 

 to the improvement of the so-called dry processes, in which 



