EXPERIMENTS IN THE CHEMISTRY. 79 



79. Place on top of the gauze a bit of camphor-gum. Ig- 

 nite it, and the flame will not pass through to the lower side. 

 Then ignite on the lower side, and extinguish the flame on the 

 upper side. 



77. The carbonic acid of a burning candle may be passed 

 through lime-water in the following manner. Take a bottle 

 arranged with tubes, as in the middle one shown in the figure 

 on page 87. From the tall tube at the left suspend a glass 

 funnel with the stem coupled to the tube by means of a piece 

 of rubber tubing. Place under this funnel a burning candle. 

 Partly fill the bottle with lime-water. Then placing the mouth 

 to the right-hand tube, draw out the air from the bottle. This 

 makes a draft over the candle, and draws its invisible smoke 

 through the funnel, down the long tube, and up through the 

 lime-water, which soon becomes milky. 



SO. The compound blow-pipe with gasometers, as shown on 

 page 238, is the most serviceable. If gas-bags are used, the 

 one for hydrogen should be twice the size of the one for oxy- 

 gen. A board should be laid on each bag, upon which weights 

 may be placed, when ready for use, so as to force out the gas 

 steadily. Turn the stop-cock so that the H will pass out 

 twice as fast as the O. Always ignite the H first, and then 

 turn on the O slowly until the best effect is produced. If gas- 

 ometers are used, press the inner receivers down to the bottom, 

 and then pour in water till it reaches nearly the top. The rub- 

 ber pipes may then be attached to the hydrogen or oxygen 

 apparatus, and the gases passed directly into the gasometers. 

 Proper pressure is produced, when the jet is to be ignited, by 

 unloosing the strings from the inner receivers, and thus taking 

 off the " lift" of the weights which equipoise them. Additional 

 pressure is secured by bearing down upon the receivers. All 

 the metals burn in the blow-pipe flame with their character- 

 istic colors. Narrow slips should be prepared for this purpose. 

 A mirror, and a cup for holding the chalk, are necessary to 

 show the lime-light. A piece of hard chalk or lime, whittled 

 to about the size of a pencil, may be held in the flame to illus- 

 trate the principle. 



87. Put in the flask two ounces of common salt and an 

 ounce and a half of black oxyd of manganese. Pour on 



