462 Scientific Intelligence. [Dec. 



alumina fell, which, as nearly as I could judge by the eye, was 

 as copious as the previous precipitate of peroxide of iron from 

 the same crystal. The salt then was not a simple persulphate 

 of iron. It contained at least two bases. Whether potash or 

 ammonia was present, I did not attempt to determine, as the 

 quantity must have been too minute to be easily appreciated, 

 even supposing it present. I made some trials to obtain a similar 

 salt, by mixing together pertrisulphate of iron and alum, and per- 

 trisulphate of iron and sulphate of alumina ; but neither by 

 spontaneous evaporation, nor by evaporating by the heat of a 

 steam-bath, could I procure any similar octahedral crystals. 

 Hitherto, therefore, the nature of this new salt remains a pro- 

 blem, which I have not been able to solve. 



But I have hit upon a method of procuring aribther species of 

 persulphate of iron, which crystallizes, and possesses some 

 curious enough properties. My method of proceeding was this. 

 I took a solution of protosulphate of iron, which had remained 

 exposed to the action of the air for above a twelvemonth, and 

 was of course almost changed to persulphate. To this solution I 

 added a quantity of sulphuric acid, and then concentrated it 

 upon a steam-bath till its bulk was reduced to less than one half 

 of its original state. On setting it aside for 24 hours, a number 

 of crystals of protosulphate of iron were deposited. The mother 

 liquor, which had a very deep red colour, was poured off these 

 crystals into a Wedgewood evaporating dish, and placed upon a 

 steam-bath at a temperature of rather more than 150°. Here it 

 remained for several days. On looking at it I was surprised to 

 find the colour much lighter, and a deposit of small white, semi- 

 transparent crystals at the bottom of the vessel. These crystals 

 were small, and so much involved in each other that I could not 

 make out their shape in a satisfactory manner, though several of 

 them seemed to be four-sided prisms. 



These crystals had an acid and astringent taste ; when exposed 

 to the air they slowly attracted moisture, and deliquesced. They 

 were soluble in alcohol, and gave that liquid a yellow colour. 

 When put into water they speedily separated into small, shining, 

 white scales, which rendered the water milky ; but they dissolved 

 in that liquid very slowly unless assisted by heat. I put four gr. 

 of the crystals into 200 gr. of water : 24 hours elapsed before 

 the solution was complete. I then added 10 gr. : in 48 hours 

 they were also dissolved : 10 gr. more were added ; and they 

 also took about 48 hours to dissolve completely. 



The solution was at first colourless, but it became distinctly 

 yellow when the quantity of salt dissolved was considerable. 



When the water was evaporated, the salt was obtained unal- 

 tered in small crystals, or more easily in the state of a white 

 crust. 



I took 15 gr. of the crystals, dried at the temperature of 150 3 , 

 and dissolved them in water. The peroxide of iron being precr* 



