OF ARTS AND SCIENCES. 121 



washed out. If the valve becomes clogged, it can generally be cleared 

 by developing pressure in the generator by means of a small charge 

 of ground marble. Otherwise, after the pressure has been relieved, 

 and the upper valves and bungs closed, the discharge valve must be 

 cautiously removed, and an opening forced through the lower bung. 

 Such details are necessary in order that others may profit by our ex- 

 perience ; but, lest the details should convey the impression that the 

 apparatus is complicated, and that the process requires skilled labor, 

 it may be stated that in this laboratory the apparatus is entirely iu 

 charge of a laboratory servant, and may be managed by any workman 

 of ordinary intelligence. It does not require more than four hours to 

 work over a single charge, and this yields 75 litres of hydric sulphide 

 solution under a pressure of 120 lbs. According to our experience, 

 this supply lasts with a class of one hundred students in qualitative 

 analysis about a month. For laboratories where the classes are much 

 smaller than this, we should recommend the smallest size generator, 

 which may be used with a single six-gallon fountain. The smaller 

 apparatus is managed in precisely the same way as the larger, only 

 taking one half the quantity of materials. It is important as before 

 to wash out in the first place all the air, and to maintain a small cur- 

 rent of gas through the vent valve of the fountain while the pressure 

 in the apparatus is rising. This of course entails some loss of hydric 

 sulphide ; but the chief loss is caused by the venting of the generator, 

 and all this gas may be utilized for the preparation of alkaline sul- 

 phides as described above, or this waste gas may be used for washing 

 out the air from a second fountain, and thus preparing it for a subse- 

 quent charge. 



For dispensing the reagent in our qualitative laboratory, we place 

 the fountain iu a cupboard and connect it by a block-tin tube with a 

 so called "draught column," Fig. 7, in the ventilating hood above. 

 From this each student draws the reagent as it is required. In quan- 

 titative work we may draw the charged water directly from the fountain 

 into the midst of the solution to be treated, using simply a common 

 rubber hose terminated by a glass tube which dips under the surface 

 of the liquid : the hose is attached to the nipple of a cajj which 

 screws on to the valve of the fountain, and by confining two or more 

 disks of linen cloth between the cap and the head of the valve (like 

 washers) we can filter the solution as it flows out. It is more con- 

 venient, however, to distribute the reagent to advanced students in the 

 well-known soda-water siphon, Fig. 8. These require no description, 

 but as the simple apparatus used for filling the siphon is not yet 

 a familiar object in chemical laboratories, we give a figure of the 



