Molecular Actions of Crystalline Particles, fyc. 105 



round which the crystallization had taken place. Where the 

 centre is not formed by a foreign body of this sort, it has fre- 

 quently been mentioned that it consisted of an opake nucleus 

 of a spongy nature, like congealed snow, which may be easily 

 accounted for. The succession of concentric layers would be 

 caused by the passage of the particles through strata of liquid 

 globules not all at the same temperature; and the radiated 

 structure indicates a gradual increase of crystalline action pro- 

 ceeding from the centre. The temperature of the hail-stones, 

 which has generally been found below the freezing-point, is a 

 further corroboration of this view. 



The formation of butter is likewise in all probability an- 

 other instance of molecular action of the same nature. It is 

 well known that after the cream has been agitated for a cer- 

 tain length of time, the globules suddenly coalesce, and by 

 their union butter is produced. The sudden appearance of 

 this product is the more remarkable, as it takes place at dif- 

 ferent temperatures, although more quickly at some than 

 others, and not gradually, as might have been expected, which 

 precludes the idea of its being owing to any caloric developed 

 by friction. The most minute observations have been unable 

 to show any material alteration in the appearance of the fatty 

 globules at the moment before the butter is formed. Little 

 doubt can be entertained of its being caused by some molecular 

 action, or engendered in the globules by the continued agita- 

 tion they have undergone. 



Some of the most permanent gases likewise exhibit pheno- 

 mena closely allied to the above, by their action on platinum 

 and other metals. According to Dulong and Thenard, pla- 

 tinum foil newly beaten has the property of acting at the com- 

 mon temperature, on a mixture of hydrogen and oxygen; but 

 after a few minutes' exposure to the air, it entirely loses that 

 power, which may however be restored to it in a stronger 

 degree than before by heating it in a covered crucible. If it 

 be kept in a covered vessel, so as to exclude the air, it will 

 retain the power without decrease for four-and-twenty hours. 



Platinum filings, made with an ordinary sized file, have the 

 same property immediately after their formation, and which 

 they retain for above an hour. It has also been observed, that 

 a hollow ball of platinum has the power of condensing and 

 absorbing different gases, which are generally disengaged at 

 a temperature below the boiling-point (Pouillet, Elemens de 

 Physique, § 131). The action of the gases on platinum in all 

 the above cases greatly resembles that of carbonic acid on 

 glass, except that not merely simple lines, but the whole sur- 

 face of the metal exerts its influence, and that the gases them- 

 selves are invisible. 



Phil. Mag. S. 3. Vol. 28. No. 1 85. Feb. 1 846. I 



