26 Mr. C. Tomlinson on the Action of Solid Nuclei. [May 8, 



exposing them for a short time to the heat of the kitchen oven or to 

 the name of a spirit lamp, or even to the temperature of boiling water. 

 For this last purpose a test-tube was thrust through a flat cork, rest- 

 ing on the mouth of a large flask containing water, which was kept 

 bciling. The bottom of the tube containing the plaster, &c, did not 

 pass beyond the centre of the flask. In about ten minutes the nuclei 

 were thus rendered inactive, and they did not recover their activity 

 in atmospheres of carbonic acid, nitrogen, hydrogen, and nitrous 

 oxide, after several days or even weeks. But they frequently became 

 active in oxygen, and generally so in oxygen or air ozonised by the 

 action of phosphorus, and always so by a short exposure to the outer 

 air, when the wind was northerly or easterly. Inactive plaster of 

 Paris has been exposed all night to the air of my garden during 

 a south-west wind, without becoming active. Fragments of pumice ex- 

 posed to the air of my laboratory for days together, without becoming 

 active, have regained their activity within ten minutes on being 

 exposed to the open air during a northerly wind. Snow was also 

 found to be active. 



The details of a few experiments may not here be out of place. 

 The wind at Highgate, from the 28th March to the 8th April, was 

 southerly and westerly. During all this time some plaster of Paris, 

 rendered inactive by heat, was freely exposed on a flat glass plate 

 to the open air of my garden, and remained inactive. On the 9th 

 the wind passed round to the east, and remained so during some hours, 

 gently blowing ; the plaster became active on solutions of sodic sul- 

 phate and sodic acetate. 



Fragments of pumice, meerschaum, and coke, rendered inactive by 

 the heat of the oven, were put into carbonic acid on the 28th March, 

 where they remained until the 9th April, when they were still found 

 to be inactive on solutions of sodic sulphate. They were exposed 

 to the air of my garden, and became active in rather more than two 

 hours. 



A similar result was obtained with inactive fragments that had been 

 kept in nitrous oxide. 



Mr. Grrenfell (" Chemical News," xxxix, 16) is of opinion that the 

 action of nuclei in bringing about the solidification of these solutions 

 is entirely due to absorption. In one of his ingenious experiments, 

 filtering paper, folded a number of times into a long spill, is passed 

 clown the neck of the flask so as to touch the solution, the effect being 

 to render it solid either at once or after some time. 



I repeated this experiment, with this modification, namely, that of 

 placing the spills in the kitchen oven for about a quarter of an hour ; 

 they were then passed down the narrow necks of some flasks which 

 they fitted with friction, and the ends were made to dip just below the 

 surface of a solution of sodic acetate (3 to 1). One of the flasks was 



