solid Hydrocarbons found in Petroleum Distillates. 91 



following arrangement was made. 



at- 



being 

 of a win 



The porte-lumiere A 

 tached to the shutter 

 dow facing towards the south, a 

 beam of sunlight was thrown by 

 it horizontally into the room and 

 concentrated by a lens of 12-inch 

 focus placed at B. At C was 

 placed an apparatus (fig. 2) con- 

 sisting of a circular horizontal 

 table adjustable up and down on 

 a vertical rod and turning with a 

 "click." Around the circumfer- 

 ence of this table were eight little " stalls 

 test-tubes or specimen-bottles. 

 By this means eight different 

 specimens could be rapidly com- 

 pared, each in succession, being 

 brought by the action of the click 

 into an identical position with re- 

 ference to the exciting light and 

 the spectroscope. This whole ap- 

 paratus was so placed that an 

 image of the sun was formed on 

 the tube or bottle nearest to the 

 lens B. A glass tank filled with 

 a strong solution of ammonio- 

 cupric sulphate was placed, as in- 

 dicated, between B and C ; and to 



this was sometimes added a plate 



of violet glass. The spectroscope 



D employed in these observations 



was generally one of Browning's 



with a single prism of very high 



dispersion, giving a range of 



3° 54/ between C and S of the 



solar spectrum ; but a spectro- 

 scope with two similar prisms by 



the same maker and one by 



Desaga of less dispersive power 



were also used occasionally. A 



small direct-vision spectroscope 



was also frequently employed to 



detect the presence of faint lines 



or bands of absorption. 

 For examining absorption-bands, every thing else 



H 2 



capable of holding 

 Fig. " 



remained the 



