Scientific IntelliyeiLce^ Sfc. 233 



VIII. — Gallic Acid in Crystals. 



MuRATORi obtains gallic acid in crystals by forming a decoction of 

 nutgalls, filtering, adding ^ or ^- of its weight of alcohol, in a well 

 closed flask, and allowing it to remain for 15 or 20 days in a cool 

 place. Gallic acid falls to the bottom in the form of a light yellow 

 crystalline mass ; the alcohol should be distilled off, the solution 

 concentrated, -^ or ^ of alcohol again added, and a new quantity of 

 gallic acid thus obtained. — Central Matt., Feb. 1836. 



IX. — Action of Oxalic Acid upon Sulphate of Iron and Sulphate 



of Copper. 



VoGEL, of Munich, has found that as oxalic acid decomposes gypsum 

 in consequence of its affinity for lime, it also completely separates 

 from the sulphuric acid, salts of iron and copper: consequently, 

 it appears to have a greater affinity for these metallic bases, 

 than even the sulphuric acid itself. It is probable, also, that 

 oxalic acid decomposes such sulphuric acid salts as have a base of 

 oxide of zinc, manganese, cadmium, &c., as Kose obtained precipitates 

 from solutions of these salts. The protoxalate of iron is a yellow 

 powder, almost insoluble in water, leaving, when heated in close 

 vessels, a plumbago-looking matter. The oxalate of copper is a 

 blueish white powder, insoluble in water, leaving behind, when 

 heated, metallic copper, with a small quantity of suboxide of copper. 

 — Journ.fur Prakt. Chim., iii. 343. 



X. — Ferrocyanodide of Ammonia. 



It is commonly stated that this salt may be obtained in octahedrons 

 by digesting pure Prussian blue in ammonia. Bunsen has found this 

 not to be the case, and recommends digesting ferrocyanodide of lead 

 with carbonate of ammonia. It is white or yellowish, translucent ; 

 easily soluble in water but not in alcohol. The aqueous solution is 

 decomposed by boiling, and by exposure to the air at common tem- 

 peratures. When the salt is mixed with chloride of sodium ; ferrocy- 

 anodide of ammonia, acid muriate of ammonia, and ferrocyanodide of 

 sodium are formed. It consists of ferrocyanogen 31*93, cyanodide of 

 ammonia 50-92, water 1715. The salt described by Berzelius has 

 a different crystalline form and contains only one atom of water.— 

 Central Matt., Feb. 1836. 



Ferrocyanodide of Ammonia and Muriate of Ammonia is 

 obtained by digesting Prussian blue with ammonia and sal ammoniac, 

 or by crystallizing a solution of sal ammoniac and ferrocyanodide of 

 ammonia. The best proportions are 2 parts Prussian blue, 2 parts 

 sal ammoniac, and 12 parts water j boil the solution, and filter it. 

 To obtain the salt completely pure, it should be evaporated in vacuo 

 over sulphuric acid. The crystals are sharp rhombohedrons with 

 lateral angles = 96"-52, and the angles of the base = 82°-40. The 

 colour is wine or citron yellow. When heat is applied, oxide of 

 iron alone remains. It consists of ferrocyanogen 25*68, cyanodide 

 of ammonia 38*01, muriate of ammonia 25*66, water 10*65 — Ibid. 



