A. W. Peirce — Existence of Selenivmh Monoxide. 167 



minutes and then cooled. At every opportunity of lower tem- 

 perature the selenium vapors would condense into dark metal- 

 lic drops which ran into larger and larger drops, like mer- 

 cury globules, seeming to separate from the dioxide vapors. 

 This treatment was repeated six times at intervals, the contents 

 of the tube showing each time the same phenomena of sub- 

 limation and condensation. Nothing was observable at any 

 time to indicate chemical change in either substance, each 

 maintaining the characteristics of its own sublimation. 



Finally the air pump was again attached and allowed to work 

 until the manometer registered no pressure. Upon breaking 

 the end of the tube by pinching it inside the rubber connector, 

 the height of the mercury column indicated the same pressure 

 as when the tube was originally sealed. When disconnected 

 the tube possessed not the slightest odor. 



This experiment was repeated with the sole modification 

 that the heating was not carried to a temperature so high, and 

 this time 0*0730 grm. freshly prepared dry selenium dioxide 

 and 0*0730 grm. powdered selenium were sealed up in the 

 evacuated tube and heated for seven hours at 180° C. and 

 finally for one hour at 200°. Upon breaking the tube under 

 conditions similar to those of the previous experiment the con- 

 tents showed no pressure and possessed no odor. Obviously 

 no gaseous product was formed under these conditions. 



I have thus been unable to find evidence of the existence of 

 selenium monoxide, either gaseous or solid, and my experience 

 goes to show that the peculiar smell attributed by Berzelius to 

 the monoxide is only developed, as Sacc found, when selenium 

 is heated in presence of moisture, and that a mere trace of 

 moisture is suflicient to produce the odor. 



In conclusion I wish to express my thanks to Prof. F. A. 

 Gooch for many valuable suggestions during this work. 



