INDUSTRIAL PROGRESS DURING THE YEAR 1875. X cv 



Miintz and Ramspacher propose to determine tannin in its 

 solutions by filtering these, under pressure if necessary, 

 through a piece of fresh hide. This combines with the tan- 

 nin, and the filtrate is entirely free from this substance. A 

 section of the skin afterward shows a line in the middle, 

 above which the skin has thus been converted into leather. 



Vogel has continued his researches on the effect of color- 

 ing matters on the sensitiveness of collodion to the various 

 rays of the spectrum, and now concludes that the action of 

 the coloring matter may be quite different, according to the 

 nature of the silver salt employed. Naphthalin red, used with 

 silver bromide and silver chloride, gives to both an increased 

 sensitiveness to yellow rays ; while f uchsin acts very differ- 

 ently, being with silver bromide in complete accordance with 

 its absorption spectrum which is similar to that of naphtha- 

 lin red but giving to silver chloride but little increased deli- 

 cacy for yellow rays, but much for the violet ones. The same 

 fact he has observed to be true of certain colorless bodies ; 

 morphine, for example, increasing the delicacy of silver iodo- 

 bromide not only for the blue and violet, but also for the 

 green, while silver bromide is completely unaffected by it. 

 Hence, to produce the effect he at first described, three things 

 are necessary : first, the coloring matter must optically ab- 

 sorb the identical color which the collodion is to be made 

 sensitive to ; second, it must unite with any free bromine or 

 iodine ; and, third, it must not decompose silver nitrate, since 

 in that case it would injure the preparation of the plates. 

 The so-called night-blue, for example, possesses the first and 

 third conditions, but fails on the second. It has no action, 

 therefore, on the sensitiveness of silver salts to light of dif- 

 ferent colors. 



Carey Lea has published a paper upon the influence ex- 

 erted by color in changing the sensitiveness of substances to 

 light. He finds, for example, that corallin increases the sen- 

 sitiveness of silver bromide to red rays, only moderately in- 

 creases it for yellow rays, and does not increase it at all for 

 green rays, contrary to the view of Yogel. He concludes 

 that there is no relation whatever between the color of sub- 

 stances and the color of the ray to whose influence they 

 modify the sensitiveness of silver bromide. 



Vogel, however, maintains that while the chloride, bro- 



