CRVSTALLIZATION PRODUCED BY VOLTAIC ACTION. 44.1 



the media of communication must be reversed, «' V c' being put in the 

 place of a b c, and vice versa. In fine, if for the plate of platina there 

 is substituted a plate of oxidable metal, we introduce into the interme- 

 diate solution the reaction of an oxide, which being in its nascent state 

 conduces to the formation of the products. The bare inspection of the 

 figure is sufficient to give an idea of tlie results that may be obtained 

 by making the requisite variations in the solutions. 



Mode of using the Apparatus when the Positive Plate is not oxidable. 

 1st Experiment. We pour into the vessel A' an alcoholic solution 

 of sulpho-carbonate of potash ; into the vessel A a solution of sulphate 

 of copper ; and into the clay of the tube abc a. solution of nitrate of pot- 

 ash : after 24 hours' trial the reaction of the oxygen and the nitric acid 

 on the solution of the sulpho-carbonate is noAv perceptible ; for we ob- 

 serve on the extremity (a') of the platina plate the products already in- 

 dicated (when the operation was supposed to be performed with a plate 

 of lead), that is to say, crystals of sulphur, of neutral carbonate of potash, 

 &c., but no carbonate of lead, because there is no oxide of this metal. 



2nd Experiment. Crystals of Sulphur ; Sulphate and Carbonate 

 of Barytes. — In the preceding apparatus we substitute for the sulpho- 

 carbonate of potash a solution of sulpho-carbonate of barytes : we shall 

 not have long to wait for the appearance of analogous reactions ; a pre- 

 cipitation of sulphur in small crystals, and a formation of sulphate and 

 carbonate of barj'tes in prismatic needles. We should perhaps by this 

 process obtain crystals of some size, if the plate of platina was so bent as 

 to form a spoon, and thus prevent the crystals formed on the surface of 

 the plate from falling to the bottom of the vessel. 



3rd Experiment. Mode of ascertaining the presence of Nitric Acid 

 and that of Hydrochloric Acid in any Solution, even ivhen those tivo acids 

 exist there in very stnall quantities. — For the plate of platina a' b' c' a 

 plate of gold is substituted : there is then poured into the vessel A a so- 

 lution of sulphate of copper ; and into the vessel A', and the clay of the 

 tube abc, a, solution of the compound which is supposed to contain the 

 two acids in combination with bases. As soon as the apparatus begins 

 to operate, the sulphuric acid expels the two acids from their combina- 

 tions, which, together with the oxygen arising from the reduction of the 

 oxide of copper, are carried to the extremity (a') of the plate of gold: 

 the yellow colour which immediately makes its appearance indicates the 

 presence of nitric and hydrochloric acids. This reaction is also obtained 

 when tubes of small dimensions are substituted for the jars. In this pro- 

 cess no part of the acids is lost ; for they are all transferred to the posi- 

 tive pole, and contribute to the production of hydrochlorate of gold. 



4th Experiment. Sulphite of Copper. — The vessel A' is filled with a 

 solution of sulphite of potash, and for the plate of gold a'b'c^ a plate of 



