S80 On definite Proportions. 



XI. Sulphate of Iron. 



Some crystallized sulphate of iron, which had been ob- 

 tained by dissolving sulphuret of iron in diliiie sulphuric 

 acid, was reduced to a coarse powder, first washed with 

 water, then digested with a little spirit of wine, in ordtr 

 to separate the superfluous sulphuric acid, and dried 

 with blotting paper. That which had crumbled having 

 been rubbed and blown off, lO gr. of this salt were ex- 

 posed in a glass retort to a high temperature, short of 

 ignition. They lost 4*63 gr. of water, I was in hopes 

 that, if all the water were thus driven awav, I should 

 be able to compute, from the analysis of the dry salt, the 

 quantity of oxygen in the protoxide which had entered into 

 combination with the acid ; hut having repeated the ex- 

 periment several times with different results, T found that 

 a part of the acid escaped with the last portions of the wa,- 

 ter, being reduced to the state of sulphurous acid. 



1.) Nine grammes of the crystallized and washed salt 

 were dissolved in water, and mixed with the nitric acid in 

 great excess, being boiled with it until the protoxide was 

 fully oxidated : muriate of baryta was then added : the pre- 

 cipitate when washed and ignited weighed 7'683 gr., con- 

 taining 2-613 of sulphuric acid, or l-06 gr. of sulphur. 

 Sulphuric acid was added, to throw down the superfluous 

 baryta, and then caustic ammonia, which aflT)rded a preci- 

 pitate of 2*59 gr. of red oxide of iron, containing 1 "790 of 

 the metal. Consequently 100 parts of iron had been com- 

 bined with 59 of sulphur. 



2.) Ten gr. of sulphate of iron, treated iu the same way, 

 afforded 8.5 of ignited sulphate of baryta, and 2-87 gr, of 

 oxide of iron. The former corresponds to 2*89 grains of 

 sulphuric acid, or 1*172 of sulphur; the latter to 1*99 of 

 iron. Consequently 100 parts of iron had taken up 38*9 

 of sulphur. 



3.) In both these experiments, notwithstanding the ex- 

 cess of acid, the sulphate of baryta had attracted a portiorj 

 of the oxide of iron, which gave it a yellowish tinge after 

 ignition ; I therefore yaried the process, so as to separate 

 first the iron and then the acid. Ten grammes of sulphate 

 of iron afforded in this manner 2-933 of red oxide of iron, 

 and 8-7 of sulphate of baryta: hence we have 2*03.5 gr. of 

 iron, 2-958 of sulphuric acid, and 1-997 of sulphur; and 100 

 parts of iroq again appear to be united to 58-9 of sulphur. 



These experiments therefore completely demonstrate^ that; 



in 



