OF ARTS AND SCIENCES. 119 



off the solution when made. But since a solution of hydric sulphide 

 is rendered turbid if left in contact with eveu a small quantity of air, 

 and since a variable amount of free hydrogen is always formed by the 

 action of sulphuric acid on common sulphide of iron, it was necessary 

 for our purpose to add to the ordinary fountain a vent cock as shown 

 in the last figure. This enables us to connect together several foun- 

 tains after the manner of Woolf's bottles as already described, and, by 

 passing the current of gas through the whole line, to drive out all the 

 air originally in the apparatus, as well as the free hydrogen subse- 

 quently evolved. Moreover, in the preparation of the solution of 

 hydric sulphide, the generator should be much larger relatively to 

 the fountains than in the preparation of soda-water. Thus we use 

 for charging the so-called six-gallon steel fountains, the "Upright 

 Generator " known as No. 40, which has a capacity below the diaphragm 

 of sixty litres. It should be here stated that the fountains are only 

 rated at two thirds of their total capacity, which is the volume of soda 

 water which is ordinarily made in them. They should never be more 

 than thi-ee-fourths filled with water. But, even with this liberal 

 allowance for gas room, the six-gallon fountains referred to will hold 

 twenty-five litres of water. It may also be stated, although the fact 

 must be evident, that a single large fountain will not give as good 

 results as several small ones of equal capacity ; since in expelling the 

 air and free hydrogen, as we have described, there would be a consid- 

 erable loss of material, if only one fountain were used. Still, in labora- 

 tories where the consumption is not great, the loss is not important ; 

 and the smallest " Upright Generator," with one six- gallon fountain, 

 will be found to be a perfectly satisfactory apparatus. 



Assuming first that the larger apparatus is used, the method of 

 charging is as follows : The large generator is too heavy to be readily 

 moved, and should be placed so that the discharge valve will empty 

 directly into a drain. Water also should be brought to the apparatus by 

 hose, — if possible, both hot and cold water, — not only for convenience 

 in charging, but also in washing. Finally, there ought to be a good 

 flue in the neighborhood, into which the waste gas may be discharged. 

 The apparatus having been thus established, the three fountains — first 

 rinsed out — are filled each with twenty-five litres of distilled water, 

 and, the valves having been secured, the fountains are connected with 

 each other and the generator by means of stout rubber hose as already 

 indicated, and the vent valve of the last fountain is connected with 

 the flue by a length of common gas hose. The generator is then 

 charged as follows : The handle is first placed so as to uncover the 

 bungs and cover the slits in the diaphragm. Through the bung A is 



