WATER. 205 



506. The explosion may be avoided, 



How may the . ' 



explosion be and a gradual combination of the gases ef- 

 fected, by evaporating a few drops of pla- 

 tinum solution in the test-tube, and igniting the residue 

 previous to the commencement of the above experi- 

 ment. A ball of fine iron wire is then crowded into 

 the end of the tube. The mixture of gases being 

 finally introduced, the least touch of flame upon the 

 end of the tube is sufficient to effect a gradual combi- 

 nation. For an explanation of the agency of plati- 

 num in the above experiment, the student is referred 

 to the chapter on metals. The iron wire serves to 

 prevent ignition, and consequent explosion, by appro- 

 priating part of the heat produced by the combination 

 of the gases. The form of the experiment last de- 

 scribed, is the only one that can be recommended to 

 the student. With the security against explosion 

 which it affords, a test-tube filled with the mixed gases 

 may be submitted to experiment. Where very accu- 

 rate results are sought, the process must be conducted 

 in a carefully graduated tube. By employing mercury 

 instead of water, the water produced in the experiment 

 may be seen. 



507. FOURTH METHOD. Still another 



Give the meth- . . 



od by oxide of method is illustrated in the figure. It con- 

 essential- 



ly, in the production of 

 water from its elements as 

 before ; furnishing, at the 

 same time, the means of as- 

 certaining the proportional weight of the gases, which 

 have taken part in its formation. The tube most 



