110 Dr. L. Playfair on a 7iexo Fat Acid 



ence between the analyses themselves, which were executed 

 on salts prepared at different times, and with scrupulous at- 

 tention to their purity, lead us to question whether some 

 other formula should not be adopted for it. Salts of silver 

 are generally anhydrous, but this does not always appear 

 to be the case ; for Crasso has lately described* a salt of 

 silver which contains water. Sericate of silver may be an 

 example of a similar compound, corresponding to Johnston's 

 sulphate of lime, in which two atoms of salt are united with 

 one atom of water. This is merely brought forward as a 

 conjecture, want of material having prevented my making 

 any further experiments on this subject. The calculated re- 

 sult, hov/ever, agrees pretty closely with the analysis. 



By calculation. 



56 Carbon 4280-36 49-94 



55 Hydrogen 686'37 S'OO 



7 Oxygen 700-00 8-19 



2 Oxide of silver 2903-22 33-87 



8569-95 100-00 



Hence the formula would be 2 Se Ag 0+ H O. 



Sericate ()fPotas/i. — Th\s compound maybe prepared by 

 melting pure carbonate of potash and sericic acid with a 

 small quantity of water. The mixture must then be gently 

 heated, in order to effect the complete saponification of the 

 acid, and afterwards evaporated to dryness on the water-bath. 

 The residue is now to be digested with absolute alcohol, 

 which dissolves the sericate of potash, but leaves the carbo- 

 nate of potash undissolved. 



Sericate of potash is very soluble both in hot and cold al- 

 cohol and water. When it is dissolved in a hot solution of 

 alcohol, it is partly deposited on cooling in the form of beauti- 

 ful white crystalline scales. It is insoluble in aether. 



We possess no data for determining how we should estimate 

 the carbonic acid in the analysis of a salt of potash formed 

 by an organic acid. Liebig states, in his treatise on Organic 

 Analysis, that the potash remains after the combustion as a 

 carbonate ; and consequently that an atom of carbon should 

 be added to the result of our analysis. But experiments made 

 on this subject by Prof. Redtenbacher, Dr. Varrentrapp and 

 myself, show that this cannot be relied on, when the salt is 

 burned with oxide of copper. Dr. Varrentrapp mixed the 

 carbonates of potash and soda with oxide of copper, and ex- 

 posed them to the action of heat in a common tube of com- 



* Liebig's Annalen, Band xxxiv. 1 . ^9, 



