Proceedings of the P olytechxic Association. 1031 



On THE FrrMiNG of Certain Acids. 

 Mr. C. Tomlinson answers an inquiry in the London Chemical 

 JVews : " Why hydrochloric acid fumes when let out into the air, 

 while ammonia, which has a much stronger affinity for water does 

 not V From his communication we extract the following : " I 

 took the specific gravity of the solution of ammonia, and found it to 

 be 0.SS9. Twenty-four drachms of this were put into a flask, and heated 

 over a spirit lamp. It at once entered into quick ebullition, and there 

 was a great head of gas bubbles from which very large bubbles expan- 

 ded and burst. The thermometer rose slowly to 100 degrees Fahren- 

 heit. When the lamp was removed the boiling ceased instantly, but 

 two or three rapid streams of small gas bubbles continued to be dis- 

 charged for some time from black specks in the glass which acted as 

 nuclei. When the temperature was at 160 degrees the .lamp was 

 removed, and the solution left to coul. It smelt of ammonia; the 

 lamp was replaced, and no gas bubbles were given off until the tem- 

 perature had again risen to about 160 degrees. The appearance of 

 ebullition was less marked than befoi'e, and the temperature rose to 

 208 degrees, at which it became stationary (barometer 28.69) inches. 

 Wlien cold, only ten drachms remained of the twenty-four. The spe- 

 cific gravity was now 0.997. The liquid had a faint smell of ammo- 

 nia, and a slight action on tumeric paper ; but on putting the glass in 

 another room, where the liquid could not re-absorb the ammonia, it 

 lost, in the course of a few hours, all smell ; it had no action on tumeric 

 paper ; it was, in fact, brought back to pure water. If a similar 

 experiment be made with a strong solution of hydrochloric acid, it will 

 be found impossible to boil away all, or nearly all the acid gas. If 

 we operate on the acid solution of the specific gravity of 2.21, it will 

 part with gas until it has a density of 1.10 (at 60 deg.), when it will 

 have a boiling point of 232 degrees Fahrenheit, and will distil 

 unchanged. We see, then, that ammoniacal gas and hydrochloric 

 acid gas are greedily absorbed by water ; there must be some impor- 

 tant difi'erence in the constitution of the respective solutions. We 

 have seen the alkaline solution is much lighter than its own bulk of 

 water ; the acid solution much heavier; that the presence of ammo- 

 niacal gas in water lowers its boiling point, while the presence of 

 hydrochloric acid in water has a contrary effect. Hence the mode of 

 combiTiation between ammonia and water must be different from that 

 between hj-drochloric acid and water. The one must be a case of 

 simple adhesion, the other of true eliemical combination .as well a& 



