PRECAUTIONS REQUISITE WITH ACTIVE CHEMICALS. 157 



action will take place, and the zinc will burn brilliantly, evolving 

 a large quantity of flakes of " zinc white " or oxide of zinc. 



Caution. In this experiment, as in all others where there is 

 apt to be a sudden develop- 

 ment of heat through chemi- 

 cal action, there is always a 

 possibility of hot particles 

 being violently ejected from, 

 and splashed out of, the Fl - 68 ' Ton S 8 ' 



vessel containing the active substances, whereby a severe burn 

 may be easily occasioned or damage done to the eyesight. The 

 greatest care must, consequently, be taken in performing such 

 experiments ; the hands may be protected by means of a pair of 

 gloves, and the eyes by a large pair of spectacles, or, better 

 still, by holding a pane of glass in the left hand in such a way 

 that the face is shielded thereby from splashes, &c., whilst what 

 goes on can be readily seen through the glass. In carrying 

 out experiments where sodium is required, or phosphorus 

 (which are both substances liable under certain circumstances 

 to set up intensely-vigorous, almost explosive, chemical action, 

 leading to the possible projection of hot burning splashes) 

 these precautions are extremely desirable, as severe injury may 

 easily be occasioned by the incautious employment of dangerous 

 chemicals. 



Another point to be strictly attended to is, that whenever highly 

 active substances are used they should never be employed in any 

 large quantity at a time ; a few grains of such materials may 

 generally be manipulated with tolerable safety, if proper care be 

 taken, whereas much larger quantities would be highly dangerous. 



Separation of Liquids from Solutions by Processes involving 

 Chemical Actions. 



Just as solid substances may be precipitated from fluids (Expt. 

 121), and gases evolved from liquid substances (Expts. 160-162) 

 by chemical actions, so under suitable conditions may liquids be 

 similarly set free by virtue of analogous changes. 



Expt. 170. To set free Liquid Fatty Matter from Hot Soap 

 Solution. Cut up a piece of ordinary household soap weighing 

 about an ounce in small pieces, and put them into a flask con- 

 taining about half a pint of distilled water ; heat the whole on the 

 water bath (Expt. 89), with occasional shaking; the soap will 

 gradually dissolve, forming soap-water such as would be used 

 for blowing soap-bubbles (Chapter XVIII.) Pour into the hot 



