380 ^^ "^"^ OXIBES OF IRON. 



Pepys 27'63 grains. The above experiments of mine were 



made at the temperature of 45°. If the vapour of water 



be subfractcd according to Mr. Dalton's formula, it will 



diminish the weight of the oxigen about one thii;d of a 



,^ , .^ grain. It follows prctly nearly from these data, that black 



contain.s27-5of oxidt- of iron is composed of 100 parts by weight of iron 



^1''^''^"° and 27-5 of oxigen. Bergman, Berthollet, Vandermonde, 



ajid Monge made many experiments on the quantity of 



hidrogcn gas given out, when jron is dissolved in diluted 



sulphuric acid; but their results difler so much among 



themselves, owing probably to the great difference in the 



purity of the different specimens of iron employed, that no 



satisfactory consequences can be deduced from them. 



Irn^i wire bum- ^' ^Vf'cn iron wire is burnt in oxigen gas, it is conTerted 



f<l in oxigen into black oxide. Mr. Lavoisier made many e?cperiments 



^'^^ ' on this combustion, from which he concluded, that 100 



parts of iron combine with between 32 and 35 parts of 



oxigen*. I repeated this experiment several tfraes, wrth 



every possible precaution to insure accuracy. All the 



trials corresponded so nearly, that it will be only necessary 



to state one of them. 11*81 grains of iron wire were burnt 



in oxigen gas. The black oxide formed weighed 15-01 



grains. Hence 100 parts of iron would by this process 



The result have been converted into 127*09 grains. This result agrees 



afjr.it'd with thepcjjj-iy ^,jth the preceding. The proportion of oxigen, 



preceding. , . , , , . • 1 ,1 . • • ■ 1 ,. . 



wlucn appears to combine with the iron, is indeed a little 



lower. But the reason I believe to be, that, during the 

 combustion of the iron, small particles of it are dis- 

 sipated in sparks, which cannot afterward be colleeted and 

 weighed. This quantity is indeed very minute ; but still it 

 is something, and maj be seen very well, when we exa. 

 mine the cloth upon which the oxide is washed. If it 

 amounted in the preceding experiment to the 20th part of 

 a grain, it would bring up the proportion of oxigen to 

 27*5, the same which was deduced from the hidrogen gas 

 emitted during the solution of iron in diluted sulphuric 

 acid. 

 The black ox- 3. When black oxide of iron is dissolved in nitric acid, 

 ide dissolved in ^^^ solution evaporated to dryness, and the dry mass exposed 



* Annales de Chimie, torn. 1, 19. 



to 



