OF ARTS AND SCIENCES. 



123 



iu charging the generator. This siphon unquestionably affords the 



most convenient mode of using hydric sulphide; and for a private 



laboratory a single siphon, well charged, 



will afford as ample a supply as will 



ordinarily be needed. It is greatly to be 



hoped that our manufacturing chemists 



may soon find an advantage in supplying 



this important reagent in such an elegant 



form.* 



When the water is charged as directed 

 above, it of course holds in solution, be- 

 sides hydric sulphide, a considerable vol- 

 ume of carbonic dioxide ; and if, under 

 any circumstance, the presence of this 

 last gas would produce an injurious effect, 

 the marble powder can be simply omitted 

 in charging the generator. In almost all 

 cases, however, the carbonic dioxide ex- 

 erts a very beneficial influence, and in 

 several ways. In the first place, it in- 

 sures the non-action of the hydric sul- 

 phide on the metallic surfaces of the ap- 

 paratus. In the second place, it protects 

 the solution from the action of the air 

 when it is drawn into an open vessel, so 

 that after a metallic sulphide has been 

 precipitated by an excess of the reagent, 

 the products may be digested in an open 

 flask or beaker without fear of oxidation. In the third place, the 

 carbonic dioxide adds greatly to the tension of the confined gas, and 

 enables us to develop sufiicient pressure to charge the siphon without 

 unnecessarily increasing the strength of the solution of hydric sulphide. 



Chemical Laboratort of Harvard College, 1876. 



Fig. 9. 



* All the apparatus here described may be obtained from the firm of John 

 Matthews, First Avenue, 26th and 27th Streets, New York, at very reasonable 

 rates. Be careful in ordering to state the use to which the apparatus is to be 

 put, with the caution that no silver plating or lead paint should be used upou it. 



