130 SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTEN. [April 7, 



''The tungsten trioxide and sodium carbonate were combined in 

 a glass bulb as in the sketch. A neutral glass is desirable for this 

 purpose, and the bulb should be made of Jena glass, which will 

 withstand the action of alkaline carbonates better than ordinary 

 glass. If sodium carbonate dissolves the glass no error will be 

 introduced, but if carbon dioxide be liberated through such solu- 

 tion, then the glass cannot be used. To determine this point a 

 blank experiment was made, which showed that the total weight of 

 the bulb and sodium carbonate remained unchanged, while 0.0017 

 grams of glass were dissolved ; hence no appreciable evolution of 

 carbon dioxide occurred. However, to prevent any possibility of 

 such loss, a platinum bulb had better be used. 



''It was found that moist sodium carbonate could be heated to a 

 constant weight, by heating for one and a half hours at a tempera- 

 ture of 300° in a vacuum ; and in this bulb the weight after stand- 

 ing several days remained unchanged. To insure complete desic- 

 cation the bulb was always heated double the required length of 

 time. A water pump was used to produce the diminished pressure, 

 and since nothing can be perfectly dried in a vacuum resulting 

 from such a pump, a calcium chloride tower was introduced. But 

 calcium chloride will not perfectly desiccate a gas, so that phos- 

 phorus pentoxide had better be used. However, for the prelimin- 

 ary experiments in hand, calcium chloride was sufficient. 



"The method of procedure was as follows: some sodium car- 

 bonate was introduced into the bulb and heated for three hours at 

 300° in a vacuum. The suction was disconnected, and after cool- 

 ing, the combined weight of bulb, sodium carbonate, and dry air 

 was obtained. Tungsten trioxide was then introduced through a 

 long funnel, the bulb was exhausted, allowed to fill with dry air 

 and again weighed. This gave the weight of tungsten trioxide. 

 The weight of the sodium carbonate, further than being present in 

 excess need not be known. Water was added and the bulb heated 

 in a glass air bath, so that the course of the reaction could be 

 watched. The mixture slowly effervesced, and when the action 

 had ceased the vacuum apparatus was attached, and the water dis- 

 tilled off. This water was tested and found to be neutral. The 

 calcium chloride tower was now introduced, and the residue, con- 

 sisting of a mixture of sodium tungstate and carbonate, was heated 

 for three hours at 300° in a vacuum. After cooling and thus allow- 

 ing the bulb to fill with dry air, it was detached and weighed. 

 This loss in weight gave the carbon dioxide evolved. It may be 

 added that the entire bulb should be inside the air bath, until the 

 water has been removed ; and then the upper portion be placed 

 outside and the temperature increased to 300°. In this way no 

 moisture will condense in the head, and the stopper remaining per- 

 fectly dry will not become jammed. The stopper should not be 

 lubricated. 



"The following results were obtained, from impure material. 



