1901.] SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTEN. 141 



atomic value of any element. Splendid as is the work of 

 Schneider, worthy as it is of high praise, there still remains the 

 fact, not to be pushed aside, that between the minimum and maxi- 

 mum values there is a difference of more than a unit. The atomic 

 value given by Schneider, Hardin and others for tungsten is 

 184 — the mean of very widely differing series. Cognizant of these 

 facts, with faith in the greater purity of our material, steps were 

 taken to repeat several older procedures. 



Preparation of Tungsten Hexachloride. 



Chlorine, free from oxygen and moisture, is absolutely essential 

 to obtain this compound pure and in comparatively large amounts. 

 The product must also be sublimed repeatedly in an atmosphere of 

 chlorine, without exposure to the air. The first condition, 

 although apparently simple, is really very difficult to attain ; and 

 after much experimenting, we cannot say that we got chlorine 

 absolutely free from moisture. But the quantity of oxychloride 

 formed along with the hexachloride may be taken as an index of 

 the amount of moisture (also oxygen) in the chlorine. 



The generator was charged with material sufficient to yield 

 chlorine an entire day without the addition of acid and consequent 

 introduction of air into the apparatus. When the flow of gas com- 

 menced to grow less only the gentlest heat was applied for a few 

 minutes to the generator. The chlorine was most completely dried 

 by conducting it through three six-inch U-tubes connected in 

 series, containing pumice stone saturated with pure concentrated 

 sulphuric acid, and in the bend sufficient acid to fill the bottom of 

 the tubes, thus causing the gas to bubble through the acid before 

 each new preparation. Indeed, it was about every fourth day that 

 a renewal was made. Only traces of oxychloride were observed. 

 The reaction of chlorine and metal took place in a combustion 

 tube of soft glass, 15 to 18 mm. in diameter and 4^ feet in length. 

 The tube was contracted in two places to the thickness of a lead 

 pencil, thus making three sections, of which the first was 3 feet in 

 length, the second i foot and the last ^ foot. A porcelain boat 

 carried the tungsten metal. The chlorine was passed through the 

 apparatus for two hours before any heat was applied. This was 

 done to expel the air. Then the burners of the furnace (to within 

 three of the boat) were lighted, beginning with those most distant 

 from the boat, the flames being small. The tube beyond the boat 



