452 JV. II. Darton — Fossils of Orange County, JS T . Y. 



Art. LV. — A new form of Absorption Cell; by Arthur 



B. Bostwick. 



The writer has devised and used the cell described below for 

 the purpose of obtaining the absorption spectra of liquids which 

 have but little selective absorption, and which would there- 

 fore have to be used ordinarily in large quantities. 



The cell is a rectangular box about six inches long by three 

 broad and three in height. The bottom and the two ends are 

 of pine wood, covered with shellac, and the two sides are of 

 ordinary looking-glass, cemented to the wood, so that the box 

 is water-tight. The reflecting surface of the looking-glass is 

 turned inward and at each of two diagonally opposite corners 

 the amalgam is scraped away so as to make a vertical slit about 

 two millimeters in width. One of these is placed close to the 

 spectroscope slit, and through the other a parallel beam of light 

 is admitted. It is evident that the box may be so placed that 

 the beam will be internally reflected in it a number of times, 

 depending upon the angle between the two, and will finally 

 pass through the second slit into the spectroscope. The length 

 of its path through the cell may therefore be varied indefinitely 

 by turning the latter, and is limited only by the decrease in 

 intensity caused by general absorption — not only in the liquid, 

 but' also at each reflection. 



A solution of bichromate of potash, so weak that a test-tube 

 full of it was of a barely perceptible yellow color and showed 

 no absorption at all when held before the spectroscope slit, 

 when placed in this cell, absorbed the whole upper end of the 

 spectrum, the F line being scarcely visible. In this case sun- 

 light was used, the beam being reflected six times, and having 

 a path whose length inside the cell was about two feet. With 

 mirrors of polished metal the result might be even better, since 

 the absorption in the glass would be eliminated. In this case 

 however the number of liquids which could be used in the cell 

 would be somewhat limited. 



Art. LVI. — Preliminary notice of Eossils in- the Hudson River 

 Slates of the Southern part of Orange Co., N. T"., and elsewhere • 

 by Nelson H. Darton. 



In a very detailed study, now nearly completed, of the for- 

 mations other than Arcbasan in central and eastern Orange 

 Co., N. Y., fossils have been discovered in many new localities 



*This Journal, Sept., 1880, pp. 197, 198. 



