On definite Proportions. 281 



in the sulphate of the protoxide of iron, the sulphur and 

 ^ron are in the same proportion as the sulphuret at a mi- 

 nimum. 



The slight excess of M5 of sulphur undoubtedly depends 

 .on some t'ritiing error in the exptrimenls, or in the data; 

 perhaps, lor instance, from having assumed a little too 

 much sulphur in the sulphate of baryta. 



Thenard has described six diflerenl combinaiions of iron 

 with the sulphuric acid, {Amu Ch. Ivi. 59.) and among 

 them a supersulphate of the protoxide. It is obtained by 

 addmii concentrated sulphuric acid to a solution of neutral 

 sulphate of ihe protoxide. Although 1 had often seen salts 

 precipitated from their solutions by acids, without receiving 

 an excess of acid, for instance the muriates of baryta and 

 of copper by the muriatic acid, yet T determined to examine 

 the lact more accurately. The fine grained white salt, 

 which J obtained in this manner, was freed from the acid 

 .which adhered to it by water and spirit of wine, then dried, 

 dissolved, and decomposed. It appeared to contain exactly 

 ^he same proportions of its component parts, as the neutral 

 s^alt ; and when it was evaporaied in a retort, it afforded 

 crystals of the same kind. Consequently Thenard'^ super- 

 fulphate is nothing more than the neutral salt, its \vhiteness 

 dcpendijig only an the state of powder in which it is thrown 

 down bv the acid. Here therefore we could not expect to 

 Cnd a combination answering to the sulphuret at a maxj- 

 pnim. 



Thenard, who considers the neutral salt which T have 

 examined as acidulated, although in a lower degree than 

 that which is thrown down by the acid, describes a neutral 

 sulphate of an emerald green colour, which is obtained 

 when dilute acid is boiled with an excess of iron filings. 

 The sulphate, which I employed in my analysis, had been 

 boiled with iron filings as long as there was any action be- 

 tween them, and yet u was by no means this emerald green 

 fait. 



I now kept a solution of neutral sulphate of the protoxide 

 of iron in a gentle heat for several davs in an open vessel, 

 and as it evaporated, I added water gradually. During this 

 operation a yellow powder was precipitated. The salt 

 V hich was left at last crystallized in oblique rhombs, and 

 had an emerald colour. A part of this salt I took out; the 

 remainder I boiled with nitric acid, and afterwards exposed 

 it in a platina crucible to a heat approaching to ignition. 

 This mass, freed from nitric acid, was dissolved in water; 

 il deposited a red powder, which I afterwards found to be 



sub- 



