38 AGRICULTURAL CHEMISTRY 



easily lost. When all is ready, add, through the thistle tube, 

 about 15 cc. concentrated hydrochloric acid (HC1), and then 

 sufficient water to carry the acid out of the trap of the thistle 

 tube. Do not apply any heat whatever. Do not collect any gas 

 until the generator has been going for about two minutes, and do 



Fig. 17. Apparatus for preparation of hydrogen. 



not attempt to light the gas as it issues from the generator. Col- 

 lect one or two cylinders of gas, adding more acid if necessary, 

 always keeping the cylinders covered, mouth downward, because 

 H is a light gas, and will readily escape if the cylinders are 

 placed right side up. 



When working with hydrogen in the laboratory, the 

 student should always exercise care, because mixtures of 

 hydrogen and oxygen are very explosive. Only a spark 

 or a near-by flame is necessary to bring about an explo- 

 sion. 



Make the following test with hydrogen: Thrust a burn- 

 ing splinter into the mouth of the cylinder of hydrogen, 

 as shown in Fig. 18. 



Questions, (i) What is the color of H ? (2) Odor? (3) Is 

 it a light or heavy gas ? (4) Does it support combustion ? (5) 



