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PROCEEDINGS OF THE AMERICAN ACADEMY 



simplify the apparatus, and to depend upon the purity of materials 

 rather than on the completeness of purifying methods for obtaining 

 pure hydrogen. Meanwhile, for reasons stated below, the writer had 

 reduced very materially the scale of his operations, and this rendered 

 unnecessary the large generator we had first employed. 



The second apparatus that was constructed is represented in Fig. 5. 

 Of this, the generator, in which hydrogen is made from pure zinc and 

 hydrochloric acid, is the same as that described by Julius Thomsen.* 

 The Wolff bottle is filled with pure granulated zinc, and the upper 

 bottle contains pure hydrochloric acid diluted about one half. By 

 means of a glass stopcock the acid is allowed to flow into the zinc 

 drop by drop, and in this way the current of hydrogen can be quite 



Fig. 5. 



closely regulated. Tubes protected by stopcocks are provided for 

 adding fresh charges of acid, and for drawing off the solution of zinc 

 chloride ; also a tube connecting the upper part of the two bottles 

 enables the operator to effect these transfers without introducing any 

 air. The gas from this generator passed first through a long potash 

 tube inclined at about 10° to the horizon, then through a tube about 

 three feet long filled with calcic chloride, then through a glass tower 

 filled with glass beads drenched with sulphuric acid, and lastly through 

 a second tower filled with phosphoric pentoxide. As many of the 

 joints as possible were made by fusing together the glass, and all the 

 others were protected by a cement consisting of equal parts of pitch 

 and gutta-percha. It will be noticed that an overflow is provided at 

 the point where the potash tube connects with the calcic chloride tube, 



* Thermochem. Untersuch., vol. i. p. 28. 



