134? Dr. Stenhouse on the. 



cause no precipitate. Parakomenic acid also closely resem- 

 bles komenic acid in its silver salts, of which it appears to 

 form two. When a solution of the acid is added to nitrate of 

 silver it occasions a copious white granular precipitate, and 

 when the acid has been previously neutralized with ammonia 

 it gives with nitrate of silver a yellow gelatinous precipitate. 

 I attempted to determine the atomic weight of parakomenic 

 acid from a small quantity of these salts, but the results were 

 unsatisfactory, and unfortunately I have not yet been able to 

 procure enough of the acid to enable me to repeat them. 



I may mention however that both salts gave less of silver 

 in the 100 parts than the corresponding salts of komenic 

 acid. Both acids also give a similar deep red colour with 

 persalls of iron, and on standing for a few hours they both 

 yield a quantity of small, hard, jet-black crystals, of which, in 

 the instance of komenic acid, a description and analysis is 

 herewith subjoined. The crystals formed by parakomenic 

 acid cannot be distinguished by their appearance and general 

 properties from those of komenate of iron, though the compo- 

 sition is probably different. 



Komenate. of Peroxide of Iron. 



When persulphate of iron is added to a cold and pretty con- 

 centrated solution of komenic acid, the liquid becomes of a deep 

 blood-red colour. After standing for some hours it grows 

 paler, and a considerable quantity of very small jet-black 

 crystals are slowly deposited on the sides and bottom of the 

 vessel. These crystals have a considerable resemblance to 

 coarsely-pounded charcoal, but they possess a much higher 

 lustre. In chemical authors komenic acid is said to form a 

 very soluble salt with peroxide of iron. This is a mistake, 

 however, and can only have arisen from the circumstance that 

 this black powder is so unlike a salt, that it has hitherto been 

 overlooked. The crystals are very hard, are gritty between the 

 teeth, and have scarcely any taste. They are difficultly so- 

 luble in either cold or hot water. When rapidly washed with 

 cold water it runs off' nearly colourless, but if the water is kept 

 for some time standing over them, it becomes of a pink colour. 

 Their solution in boiling water has a pale red colour. Their 

 powder is dark reddish-brown. They were dried at 212° F. 

 and subjected to analysis. Percent. 



I. 0-4230 gramme gave 00784 peroxide of iron = 18-53 

 II. 0-4690 0-086 =1831 



III. 0-4325 0-081 =18-72 



IV. 0-3434 0-064.5 =18*76 



I. 0-3534 gramme, when ignited with chromate of lead, gave 



0*450 carbonic acid and 00953 water. 



