WHEELER & LUEDEKING — IODINE IN BLOWPIPIXG. 677 



and allowing it to set. Before perfectly hard it is cut into conve- 

 nient pieces, about 4 inches long by i J wide, with a knife or spa- 

 tula, cutting it while moist to prevent the breakage of the sheet if 

 attempted when dry. Before the liquid plaster is poured on the 

 flat surface, this must be very slightly oiled to prevent adhesion. 

 (But little oil should be used lest the plaster turn black by its 

 charring.) 



The substance is placed on one end of these tablets, moistened 

 with a few drops of the hydriodic acid and then gently heated in 

 the oxidizing flame. It is necessary to use the oxidizing flame 

 to prevent the deposition of soot, which interferes and tends to 

 mask the films if the reducing flame is employed. 



The hydriodic acid converts most of the metals into iodides, 

 which, on account of their volatility, pass oflMn vapor on heating 

 and are condensed as colored coats on the further end of the ta- 

 blet. The beginner must not confound the brownish coat that 

 is given ofl' by the decomposition of the hydriodic acid itself; 

 this brownish iodine coat will completely volatilize on standing 

 a few minutes, especially if breathed upon. 



The color of the coats produced by the different metals and me- 

 talloids are herewith described. 



COLOR OF THE IODIDE COATS. 



Arsenic — A reddish-orange. 



Lead — A chrome-yellow. 



Tin — A brownish-yellow. 



Silver — A bright yellow while hot; faint grayish-yellow when cold; is 

 close to the assay. 



Antimonv — An orange-red. 



Mercury — Scarlet and yellow, the yellow changing completely to scarlet 

 on standing. 



Selenium — A reddish-brown. 



Tellurium — A purplish-brown. 



Bismuth — A chocolate-brown fringed with red near the assay. 



Cobalt — A greenish-brown edged with green; the brown color is evanes- 

 cent, changing into faint green, especially when breathed upon. 



Molybdenum — A deep ultramarine; is close to the assay, and is the per- 

 manent oxide M02O5. 



Wolfram — A faint greenish-blue ; is a permanent oxide, W02O5 ; is close 

 to the assay, and is brought out stronger by dropping on more acid 

 after the operation. 



