498 Lord Blythswood and Mr. H. S. Allen on 



§3. Experiments carried out by the Authors show that it is 

 only necessary to increase the size of the charcoal receptacle 

 in order to produce a high degree of exhaustion in a large 

 discharge-tube without the use of a pump. The first attempt 

 made (Jan. 30, 1905) was to exhaust an old X-ray bulb, three 

 inches in diameter (capacity 250 cc), This was attached to 

 a drying-tube containing phosphorus pentoxide, and to a bulb 

 of capacity 200 cc. containing about 65 grams of charcoal*. 

 The apparatus was set aside for some days before it was used 

 so that the air might be dried. Before the charcoal bulb was 

 cooled, both it and tha discharge-tube were heated strongly to 

 drive off as much gas as possible. The apparatus was then 

 sealed, and when the charcoal bulb was sufficiently cool it 

 was placed in liquid air. During the process of exhaustion 

 the focus tube was heated, and during the later stages the 

 discharge was passed through the tube to drive off gas from 

 the electrodes. 



The tube was sealed off after the charcoal had been cooled 

 for one hour, and the vacuum produced was so good that the 

 tube had to be heated in order to allow the discharge to pass 

 through it. 



A second focus tube, four inches in diameter (capacity 

 675 cc), was successfully exhausted with the same charcoal 

 bulb (Jan. 31). 



§ 4. In the next experiment the drying-tube was discarded 

 altogether, and a new X-ray bulb, five inches in diameter 

 (capacity 1150 cc), was attached to the charcoal absorber 

 (fig. 1). The following notes show the progress of the 

 exhaustion : — 



Commenced to heat discharge-tube and charcoal. 



Apparatus sealed. 



Charcoal bulb placed in liquid air. 



Discharge begins to pass. 



Both electrodes covered with a velvet glow. 



Discharge fills the whole bulb. 



Some green fluorescence. 



Shadow of the electrodes thrown on the tube by cathode 



rays. 

 X-rays beginning. 

 Discharge-tube sealed off. 



The result of this experiment was a somewhat " soft " 

 X-ray tube. 



Several similar X-ray tubes were exhausted, and exhibited 

 the same succession of changes at practically the same time 



* The charcoal used in the experiments we have carried out Avas of 

 two kinds, the first made from lignum vitce, the second from the shell 

 of the cocoanut. The material was packed into an iron pot closed with 

 a lid provided with a small vent hole, and was heated in a gas furnace for 

 some hours. 



11.25 A.M. 



11.35. 



11.45. 



11.50. 



12 NOON. 



12.7 p.m. 



12.9. 



12.12. 



]2.30. 



12.50. 



