326 Use of alkalized Oxide of Iron in Calico Printing. 



off the liquid, which still had an astringent taste, and pre- 

 served it in a glass. After some time I found in it very 

 beautiful colourless and transparent crystals, which resem- 

 bled alum. Having immersed it in an alkaline solution of 

 prussic acid, its surface became covered with the most 

 beautiful Prussian blue, which sut^'cred itself to be removed 

 by washing without its colour being changed. This blue 

 was reproduced as long as any of the crystals remained. In 

 the air these crystals became yellowish, in consequence, no 

 doubt, of the solar rays having disengaged from them a 

 portion of oxvgen; for when I examined them afterwards^ 

 I found that they were nothing else than hyperoxygenated 

 sulphate of iron, Thi-s salt is insupportably astringent. 

 When diluted with a great deal of water a precipitate is 

 produced, and speedier when the mixture is exposed to 

 heat.. I'he filtered precipitate had a most beautiful yellow 

 colour. A high temperature, however, deprived it of its 

 rust colour, as it by these means lost its excess of oxygen. 



On repeating this experiment I always obtained the same 

 result ; and w hen I exposed the white insipid residuum in 

 a a;lass retort, combined with a Woolf's apparatus, to such 

 a degree of heat as brought it to a state of ignition, the acid 

 was disengaged from it in the form of suljjhureous and 

 sulphuric acid, accompanied with a mixture of oxygen gas. 

 The oxide of iron obtained in the retort after the experi- 

 ment was of a brownish red colqur, and fit for polishing. 



If the quantitv of the sulphuric acid be lessened, there 

 w\\\ be obtained, in like manner, a white pulverulent resi- 

 duum, which, notwithstanding its insipidity, dissolves in 

 an equal part of warm water, and after cooling, and being 

 left some time at rest, produces crystals. 



I'he hyperoxvgenated oxide of iron, obtained by caustic 

 alkali, from Stahl's tincture of iron, or any other acid so- 

 lution of that metal, when precipitated and again dissolved 

 in sulphuric acid, with some excess of the iatter, gives 

 also beautiful crystals of hvperoxygenated sulphate of iron. 



The common sulphate of iron, which is ox)'gcnated by 

 nitrous acid, or by the absorption of nitrous gas, does not 

 crystallize ; and, when the evaporation is not continued to 

 dryness, acfjuires the consistence of syrup or of honey. 

 But if a fifth or a sixth part of concentrated sulphuric acid 

 be added, a confused crystallization is immediately pro- 

 duced which forms a compact mass. This proves that 

 hvperoxygenated crystallized sulphate of iron requires a 

 greater quantity of acid than the common sulphate. 



3 The 



