Journal of Applied Microscopy. 553 



rugated at the side by cutting out pieces, is a convenience, but not a necessity. 

 Such a stopper may be of cork or wood, or, what is best, of rubber. It should fit 

 with sufficient tightness to prevent the submerged bottle from coming loose, 

 spilling the zinc, and rising as a result of the buoyancy of the contained gas. A 

 glass or rubber tube (such as shown in the illustration at D) is passed through 

 a hole in the cork so that the end within the bottle reaches to the bottom of 

 the bottle, B; the length of the projecting end of the tube will depend 

 upon the depth of the outside container, and the distance to which it will be 

 desired to conduct the gas to other apparatus. It is best to make this tube of 

 glass, although rubber tubing will do ; where fragility is an objection, lead might 

 be substituted, although the authors have never used anything but glass. The 

 conducting tube, D, should have an internal diameter of .5 to 1 cm., and should 

 be sufficiently heavy not to break easily. The outside container, A, may be a 

 wooden bucket, crockery jar, ordinary battery jar, or Whitall-Tatum museum 

 jar, with a perforation in the lid through which the tube can be passed ; a large 

 sized Millville gas jar, such as made by Whitall-Tatum, will be found most con- 

 venient. We used such a jar for some time, but it was accidentally broken, and 

 since that time we have used an ordinary museum jar ; when the apparatus is 

 not in use we lift out the bottle containing the zinc and set it to one side, and 

 stopper the jar containing the sulphuric acid. To use the apparatus, a sufficient 

 quantity of scrap zinc, or zinc turnings, is placed in the bottle, B, the bottle is 

 then laid upon its side to permit of the insertion of the tube and stopper. The 

 bottle is now turned upside down as in the illustration, and inserted into the 

 diluted sulphuric acid in the outside container. The height of the liquid in the 

 outside container should be so adjusted that when the bottle containing the zinc 

 is pushed down as far in the sulphuric acid as it will go (and the acid permitted 

 to rise to its own level within the bottle containing the zinc), the acid will not 

 come nearer than two cm. of the end of the tube within the bottle, B. The object 

 of this precaution is, of course, apparent. Should the acid be admitted suffi- 

 ciently near the bottom of the bottle (which is now the top) it would run over 

 into the tube and form a trap at the bottom, or if the tube is small it might be 

 carried orr into the apparatus with which the tube is connected. At the external 

 end of the tube a piece of thick rubber tubing, E, is attached, and a Mohr's 

 pinch-cock, F, is adjusted so as to collapse it. The rubber tubing may be 

 attached to anaerobic culture apparatus of any kind, or to any other piece of 

 apparatus which it may be desired to use. If, at any time, the exit of the gas 

 from the tube be prevented, the acid is forced away from the zinc by the con- 

 tinued generation of gas, and in a very short time chemic action is arrested. 

 The apparatus may be used for the generation of sulphuretted hydrogen, or, with 

 slight modification, of carbon-dioxid, etc. 



The points which have recommended the apparatus to us are : (1) its sim- 

 plicity, (2) its cheapness, (3) any student can make such apparatus from 

 materials always available, (4) it may, by some of the suggestions already given, 

 be kept practically always ready for use, (5) it is not easily broken, and all the 

 parts may be replaced quickly and cheaply, (6) it is efficient. 



