288 Prof. G. Wiedemann on the Magnetic 



II. 



Iron contained in 



10 cub. centinis. fe : SO3. x. y. 

 gram. 



0-603 100: 75-9 53*2 0*62 



0-589 84-0 45-2 0-65 



0-577 92-6 33-2 0-72 



0-566 99-6 25-5 0-75 



0-560 103-8 19-6 0-77 



0-554 108-2 18-4 0-75 



0-540 117-6 13-8 0-71 



0-515 135-2 10-7 0-66 



0-494 153-1 7-4 0-60 



From these observations it follows: — 



(1) If to a watery solution of colloid ferric oxide in a little 

 sulphuric acid continually larger amounts of hydrate of sul- 

 phuric acid be added, the quantity of ferric sulphate in the 

 solution gradually increases, while a portion of the colloid 

 oxide and a part of the sulphuric acid persist uncombined 

 beside it. Even when the quantities of sulphuric acid and ferric 

 Oixide correspond to the same number of equivalents, only about 

 75 per cent, of them are combined, while 25 per cent, of the 

 equivalents of sidphuric acid and ferric oxide are free in the 

 solution. If the amount of sulphuric acid is less than corre- 

 sponds to one equivalent of the dissolved ferric oxide, then the 

 quantity of ferric sulphate formed increases at first somewhat 

 more slowly than corresponds to the accession of sulphuric 

 acid, then gradually approaches a maximum ; so that half an 

 equivalent of acid added to the solution besides the first engages 

 about 15 per cent, more, a further half-equivalent about 4 per 

 cent, more, of the equivalent of ferric oxide. On employing 

 about 4 equivalents of sulphuric acid to 1 equivalent of ferric 

 oxide, nearly all the oxide combines with the acid ; the maxi- 

 mum is so nearly reached that the deviation from it is covered 

 by the errors of observation. 



(2) With variation of the water-content of the solutions, 

 whether the same number of equivalents of ferric oxide and 

 sulphuric acid or different proportions of them be employed, 

 the proportion of the ferric sulphate formed, on the one hand, 

 and of the free acid and free oxide, on the other, do not change 

 very considerably. From this proposition, if it may be ex- 

 tended beyond the limits of the experiments, it follows directly 

 that, if on the employment of equal numbers of equivalents of 

 base and acid the salt formed were insoluble (instead of being- 

 soluble like ferric sulphate), after the separation of the formed 



