66 THE FOOD OF PLANTS 



in the side tube, bubbles of gas collecting in the neck 

 of the bottle instead. Any young healthy plant (flower 

 or weed) will do for this experiment. 



Experiment 6. The cork should be cut in half and 

 fitted round the stem, so as not to injure the young bark. 



Experiment 8. In some experiments where heating 

 is necessary a spirit-lamp is described as being used, in 

 others a Bunsen burner. If gas is available, a Bunsen 

 burner, provided with a rose, will be found the most con- 

 venient. When gas cannot be obtained, a spirit-lamp 

 will do instead for most of the experiments. When a 

 high temperature is required, as in the burning to ash of 

 the leaf, or the heating to redness of the soil, a spirit- 

 lamp will not do. Petroleum blowpipes can now be 

 obtained which are perfectly suitable for this purpose, or 

 a small charcoal fire will do as well. 



Filter -paper is usually sold cut into circular disks. 

 One of these should be folded in half, and then folded 

 again into a quarter of the original size, then opened 

 with the finger so as to form a little cone-shaped bag, and 

 slipped into the glass funnel, and held there while it is 

 moistened with a little water. It will then stay in position. 



Experiment 12. The soil may take several hours 

 to settle and leave the water clear, and is so finely divided 

 that some of it will pass through the filter-paper if we 

 try to filter it. This experiment therefore requires some 

 patience. 



Experiment 14. Condensers of various forms, and 

 made of different materials, will do for this experiment. 

 The one shown in the diagram is made of glass. A 

 piece of stout block-tin tubing, surrounded by an outer 

 tube of sheet-tin, does very well. The can described in 

 Experiment 30 may be used to supply water to condense 

 the steam, the tap being connected to (a) by a piece of 

 india-rubber tubing. 



Another tin can, with a block-tin tube passing through 

 a cork, can be used as a boiler. In fact, with the assist- 



