218 [Dec. 12, 



thin globe of glass upon the form of fig. 2 while in a molten state, and 

 cutting off the superfluous portion when cold (see fig. 5). 



The most useful form of vessel is that of fig. 5. In some cases 

 I have employed vessels similar to that of fig. 1, with a series of 



Fig. 3. Fig. 4. Fig. 5. 



annular spaces within each other, to as many as twelve, and to a size 

 of 8| inches diameter*. 



3. Nearly fill the inner circular space and the annular groove with 

 pure mercury, and cover the mercury to about half an inch or more 

 in depth with a filtered solution composed either of 10 grains of cya- 

 nide of mercury and 100 grains of hydrate of potash dissolved in 2J 

 ounces by measure of hydrocyanic acid containing 5 per cent, of an- 

 hydrous acid; or of 10 grains of cyanide of mercury dissolved in a 

 mixture of 3 ounces of hydrocyanic acid and ^th of an ounce of strong 

 aqueous ammonia : the latter solution must be used directly after it 

 is made, because it soon decomposes and loses its vibrating power. 



4. Take either two or three of Grove's cells, containing platinum 

 plates about 6 inches long and 4 inches wide, connect them intensity 

 fashion, and immerse the positive terminal platinum wire in the cir- 

 cular pool of mercury, and the negative wire in the annular 

 ring of mercury, or five Smee's cells, the acting surface of each 

 silver plate being equal to 30 square inches, charged with one 

 measure of sulphuric acid and nine of water, will do equally well. 

 The polar wires should be guarded from contact with the electrolyte 

 by small tubes of glass melted upon them, and reaching nearly to 

 their extreme points, to prevent dissolving of the platinum and evolu- 



* I beg to acknowledge the assistance I have received from Messrs. Osier, glass 

 manufacturers, and their talented manager, Mr. Percivall, in the construction of 

 these and other glass vessels of novel shapes. The above cups may be also ob- 

 tained of Messrs. Elliott, Brothers, 30 Strand, London, 



