Cyanides of the Metals. 57 



same field, may lead to a more precise knowledge of their 

 character and constitution. 



2. In systematic works on chemistry reference is made to 

 this subject in a very general way. The sum of such infor- 

 mation may be thus expressed : — " The soluble cyanides of 

 the alkaline metals, potassium, sodium, &c., dissolve the in- 

 soluble cyanides of the metals proper, forming double salts, 

 which are generally crystallizable :" the probable constitution 

 of only a very few of these salts are given. 



3. From the researches of L. Gmelin upon the metallo- 

 cyanurets, which were published many years ago, it would 

 appear that there are two classes of compounds in which other 

 metals are found to replace the iron in the yellow and red 

 prussiate of potash, and to form indeed metallo-cyanurets and 

 sesquicyanurets of potassium, &c. There seems however to 

 be a singular indefiniteness on this subject in chemical works ; 

 for Turner, in his ' Elements,' 5th edition, p. 779, says, that 

 " L. Gmelin has obtained a double cyanuret of zinc and po- 

 tassium, in which the zinc acts as iron in the ferro-cyanurets." 

 He also says, " that a cobalto-cyanuret of potassium, and si- 

 milar double cyanurets of nickel and cobalt, may be prepared 

 in the same manner as the preceding salt;" and further, 

 " that Gmelin procured the cobalto-cyanuret in yellow cry- 

 stals, similar in composition and form to ferro-cyanuret of po- 

 tassium." The salts here described are evidently analogous 

 to the yellow prussiate of potassa, or ferro-cyanuret of po- 

 tassium ; but on referring to Professor Graham's * System,' we 

 find there described salts of cobalt, chromium and manganese, 

 not analogous to yellow prussiate of potash, but similar in 

 symbolic constitution to the red prussiate of potash, that is, 

 metallo-sesquicyanurets having a supposed salt radical in 

 which these metals replace iron to the formation of cobalti-, 

 chromi-, and mangani-cyanogen ; no mention is made what- 

 ever of the existence of compounds similar to yellow prussiate 

 of potash, or of a cobalto-, chromo-, and mangano-cyanogen. 



On turning to Berzelius's Traite, tome ii. p. 115, we find 

 a description of the same zinco-cyanuret of potassium, or, as 

 he names it, cyanuri zincoso-potassique, analogous in compo- 

 sition to the yellow prussiate of potassa, in which zinc is found 

 to replace iron. He says, " The existence of this salt, of which 

 the discovery is due to L. Gmelin, leads us to presume that 

 zinc has a series of double cyanurets, like iron, nickel, &c." 

 Here also Berzelius corroborates the statement made by Dr. 

 Turner, and speaks of these compounds as analogous to the 

 yellow prussiate of potassa, or as metallo-cyanurets. Turner 

 mentions (p. 780) that Gmelin's observations upon the nickel, 

 copper and zinco-cyanurets have been confirmed by a late 



