152 Dr TURNER'S Chemical Examination 



vent the tube from bending while softened by the heat, two or 

 three pieces of tobacco-pipe were tied to it longitudinally by 

 means of iron-wire. But when it was wished to prepare the 

 oxide at a very high temperature, the material was put into a 

 small tube of porcelain, and then introduced into a gun-barrel 

 which was exposed to a full white heat in a common wind-fur- 

 nace. A supply of hydrogen gas was procured in the usual 

 manner from zinc and dilute sulphuric acid ; but before coming 

 in contact with the oxide of manganese, it was purified by being 

 transmitted through a strong solution of potash, and then dried 

 by the chloride of calcium. At the close of the process, the prot- 

 oxide was of course preserved in an atmosphere of hydrogen gas 

 until it was quite cold. 



The abstraction of oxygen commences at a temperature be- 

 low that of redness ; and when the peroxide is employed, it be- 

 comes red hot by the caloric evolved during the formation of wa- 

 ter, considerably before the tray which supports it is rendered 

 luminous by the heat of the fire. It appears nevertheless from 

 all my experiments that a strong heat is requisite in order to 

 convert all the red oxide into the protoxide. When the process 

 is conducted at a low red heat, I uniformly found that on putting 

 the product into dilute sulphuric acid, which instantly dissolved 

 all the protoxide, a portion of the red oxide came into view. 

 This affords a sure criterion of the operation being complete ; 

 for the pure protoxide dissolves without residue in dilute sul- 

 phuric acid, and yields with it a perfectly colourless solution. 

 There seems to be no risk of decomposing the protoxide by the 

 employment of a high temperature. I have exposed the recently 

 prepared protoxide a second time to the action of hydrogen gas 

 and a long continued bright red heat without the weight being 

 changed in the slightest degree ; and after exposure to the same 

 gas and a full white heat for an hour, it dissolves in dilute sul- 

 phuric acid without the slightest effervescence. 



