HERO'S ENGINE. 



41 



steam pressure, the first steam-engine in fact, was constructed on 

 this principle about 120 B.C. by Hero of Alexandria, and termed 

 the JSolipyle. Fig. 20A 

 represents a form of this 

 engine. 



Expt. 35. To make 

 Water Boil by pouring 

 Cold Water over the Ves- 

 sel containing it. This 

 most remarkable paradox 

 results in consequence of 

 the principle that water 

 boils at a lower temperature 

 when the pressure upon it 

 is diminished. Obtain a 

 strong glass flask and an 

 india-rubber cork fitting it 

 tightly. Half fill the flask 

 with water and support it 

 on a retort-stand (fig. 6), 

 and boil it over the gas or 

 spirit-lamp flame, taking 

 care that the cork is not in 

 the neck, so as to give free 

 vent to the steam. After 

 a few minutes, when the 

 steam is issuing vigorously, 

 remove the lamp, and at 

 the same moment cork up 

 the boiling water. Take 

 hold of the flask with a 



Fig. 20 A. Hero's Engine. The ^Eolipyle 

 F. Fire; C. Cauldron for Water; P. "Pipe 

 for Steam ; Q. Globe ; N\ N* Nozzles, 

 Steam Exhaust (from Jamieson's Steam 

 Engine). 



cloth and turn it upside down, supporting it in the ring of the 

 retort-stand (fig. 21). On pouring water slowly on to the upper 

 end of the flask the water in the lower part will commence boiling 

 vigorously, soon stopping if the supply of cold water is discon- 

 tinued, but again commencing to boil on pouring on more water. 

 If the flask be of good glass it will not crack under the operation, 

 which may be repeated at pleasure, heating up the water to boiling 

 again over the ilame (after removing the stopper) when it has be- 

 come too nearly cold to boil, any more under the influence of cold 

 water. 



The principle involved in this experiment is used in preparing 

 a number of articles of food (condensed milk, sugar, extract of 

 beef, &c.), medicinal extracts, and such like substances, where it is 



