2(\0 



Calcium Sulphide. 



The calfiuiu sulphide is the luiniuous sulpliide as prepared liy E. H. 

 Sarg( nt & Compauy, Chemists, of Chicago. The sulphide was spread on 

 a cardboard with mucilage and excited by sunlight. A tin can was 

 placed around the iron pipe and aluminum window jilaced in the tin 

 can. \\'ith this aiTangement some of the external heating effects were 

 eliminated. 



.3 7 //M P. 

 60 StC. 



I'hotographs III and IV were taken with the sulphide screen parallel 

 to the aluminum window so that the rays must fall on the back side of 

 the screen while their effect was photographed from the front side. 

 Photograph III was taken with the sensitive plate about 4 cm. from 

 the screen while IV was less than 1 cm. and in no case was the sulphide 

 screen more than 25 cm. from the source. In III the exposuivs were 

 alternated so that 2, 4, 6 and 8 were exposed to all radiations that 

 might come from a Welsbach burner and pass through an aluminum 

 window, while 1, 3, 5 and 7 were taken when a lead screen was placed 



