Miscellanies. 399 



moistened with alcohol, the mercury soon rises, acetic acid is formed 

 without the least trace of carbonic, and in a week or a fortnight the 

 oxygen is completely absorbed. 



In the air, it instantly inflames hydrogen. Its specific gravity is 

 about 16. It is therefore nothing more or less than metallic platina 

 extremely divided, acting like spongy platina, only in a more intense 

 degree. 



Metallic platina precipitated by zinc, from its acid solution pos- 

 sesses the same properties. 



The platina black (to avoid periphrasis) possesses in the highest 

 degree the property of absorbing and retaining a multitude of gases. 



If it is not boiled well in water, or if, before drying it, it is mois- 

 tened with spirit of wine, the latter cannot be expelled entirely even un- 

 der the air pump. If, in this condition, it is heated to the temper- 

 ature of boiling water, it begins to ignite, and burns the paper on which 

 il is placed. Even though entirely deprived of alcohol, and after be- 

 ing dried in an exhausted receiver aided by the presence of sulphu- 

 ric acid, if brought suddenly into contact with air, it becomes occa- 

 sionally so heated by the absorption as to ignite and burn the paper. 



The solution of chloruret of platina in potash, being mingled with 

 a notable quantity of nitrate of copper forms by boiling in spirits of 

 wine, a precipitate which though it contains at least twice as much 

 oxide of copper as platina, retains the property of igniting with al- 

 cohol. 



According to Mr. Doebereiner, one hundred grains of platina 

 black absorb twenty cubic inches of hydrogen gas. This reduced 

 to comparative volumes gives one to seven hundred and forty five, 

 which sufficiently accounts for the great elevation of temperature and 

 ignition with hydrogen or alcohol. 



Even iron, possesses an analogous property. If obtained by the 

 reduction of its oxides by means of hydrogen ; it is in such a state 

 of extreme division as to combine with oxygen, so rapidly as to 

 inflame at the common temperature. 



Both the black and the spongy platina lose the property of infla- 

 ming by continued use, owing to their becoming more dense or less 

 porous, or from having their pores obstructed by foreign matter ; or 

 from the air which they contain losing its oxygen. The method of 

 restoring the property is to boil it in nitric acid, which has no other 

 object than to expel and replace this air. Boiling the sponge in 

 water answers the same purpose. 



