316 Kenneth A. Mlclde: 



Another set of needles and pieces of iron wire similarly cleaned 

 would not float at first, but on being kept in a desiccator for 

 two days would float on the surface of distilled water. Similarly 

 some particles of sulphides when washed with alcohol would 

 not float, but on exposure for some time floated. With a pre- 

 liminary Avash in dilute sulphuric acid prior to the other cleans- 

 ing, the behaviour of the needles and wire was the same as in 

 the case of the other method of cleansing. 



This preliminary treatment would remove any oily matter 

 present. When the needles were dried by the aid of a lens and 

 the sun's rays, their floating properties seemed to be improved, 

 If the needles were handled they were found to float much 

 more readily, becoming greasy by contact with the fingers. 



These experiments show that perfectly cleaned needles and 

 iron wire will float on the surface of distilled water under the 

 following condition, viz., (a) if the watefr is allowed to stand 

 for some time in contact with the air, (b) if the needles and 

 wire are allowed to remain exposed to the air for sufficient 

 time. 



In the first case probably a layer of fine dust collects on the 

 surface of the water, and in the second case probably the attach- 

 ment of the air becomes greater after a certain time has elapsed. 



3. Cleaned and uncleaned pieces of iron wire on being- 

 immersed in a saturated solution of carbon dioxide showed the 

 following results, respectively: — 



The cleaned pieces collected very few bubbles on their sur- 

 face, and the uncleaned pieces were at once covered with a 

 frost of bubbles, and caused to float to the surface. If one of 

 the cleaned pieces is rubbed between the fingers it behaves simi- 

 larly to the uncleaned wire, and is caused to float. These ex- 

 periments also show that the gas attachment is enchanced by 

 the presence of some oily material on the surface of the metal. 



In order to compare the amount of gas given off from oiled 

 and unoiled surfaces the following test was carried out: — Tavq 

 cubical pieces of galena of approximately the same size with the 

 same extent of surface exposed were taken, one of which was 

 greased with a very small amount of vaseline. The two pieces 

 of galena were then placed under inverted separating funnels 



