Volume Changes attending Mixture. 501 



into that region, condensed, and floated on the heavier and 

 more aqueous portion. Such a layer is rather apt to be over- 

 looked, but its growth may be watched in comfort after the 

 temperature has fairly begun to sink. 



§ 259. It should also be remarked that whdle a 12*64- 

 per-cent. solution at 180° has only a slight etching-action on 

 glass, the 62*35-per-cent. solution caused the surface of the 

 glass (soft German) to peal off in visible scales when heated 

 to 150°-160°, acting like a caustic alkali. This may be the 

 reason of the bursting of the 75*76-per-cent. tube, which had 

 a wall-thickness of 2*5 millim. and an internal diameter of 

 9 millim. It is well to remember, therefore, that a tube 

 which has withstood a pressure due to a certain temperature 

 may afterwards give way when even at a lower one. 



§ 260. I have not succeeded in separating ethylamine from 

 water by heat in closed vessels. But by the closest analogy 

 we must expect both that body and ammonia itself to leave 

 the water with which they are combined as subcryohydrates 

 (§§ 235, 233); and at some very high temperature and pres- 

 sure to exhibit nearly complete insolubility with that liquid. 

 All of these liquids contract with water and evolve heat. 



§ 261. Tetrethylammonium Oxide. — Looking on aqueous 

 ammonia as being a solution in water of the oxide NH 4 HO, the 

 comparison between ethyl-, diethyl-, and triethyl-ammonium 

 oxides on the one hand, and tetrethyl-ammonium oxide on 

 the other, in regard to their solubilities in water being affected 

 by heat, should present many points of interest both to the 

 physicist and to the chemist. The following experiment may 

 be noted ; for although it brings us but little further in the 

 immediate direction of our inquiry, it confirms the statement 

 that a solution of tetrethylammonium is decomposed on con- 

 centration by evaporation. A 10-per-cent. solution heated in 

 an oil-bath to 180° gives off a permanent gas which ultimately 

 may burst the tube. This is no doubt defiant gas. At the 

 same time oily drops which float are formed in the tube; 

 on cooling, they disappear. This is evidently triethylamine 

 containing water; the reaction being 



(C 2 H 5 ) 4 , NHO = (C 2 H 5 ) 3 , HNHO + C 2 H 4 . 

 And it appears that this known decomposition is brought 

 about by heat alone without concentration. 



§ 262. Tetramethylainmonium Oxide (a 10-per-cent. solu- 

 tion) does not show any separation at 200°, but begins to 

 solidify at —16°. The tetrethyl compound of the same 

 strength also solidifies in an ice-salt cryogen. 



§ 263. Ethylic Ether may be here mentioned as a liquid 

 which, though only slightly soluble in w T ater, forms with it a 



