408 Dr. Forchhammer on a Salt composed of [June, 



oxide was afterwards dissolved in muriatic acid, and again tried 

 with nitrate of barytes, which occasioned a degree ofturbidness 

 that indicated rather more sulphuric acid than would have been 

 required to saturate the very slight trace of alkali. 



it was thus proved by direct experiments that three parts of 

 sulphuric acid are combined with peroxide of iron and one part 

 with ammonia ; it is extremely probable that the excess of 

 sulphuric acid in the last experiment is derived from some per- 

 sulphate of iron uncombined with ammonia, and upon this also 

 depends the yellow colour, and this, as already mentioned, may 

 be removed by repeated crystallization, a little subsulphate 

 being deposited. The salt which I have now described is com- 

 posed of 



Persulphate of iron 41-807 comp. of 25-337 acid + 16-470 oxide 

 Sulph. of ammonia 12*366 8*649 acid + 3-717 amm. 



Sulphate of alumina 0-870 0-610 acid + 00-260 alum. 



55-043 



Although the quantity of water contained in the salt appeared, 

 as already stated, to be 43-48 per cent, by direct experiment, yet 

 it is well known to be difficult to deprive a salt of all the water, 

 unless it be heated to redness, which the nature of this salt 

 would not admit of. If we assume the ammonia or the sulphuric 

 acid combined with it to be one atom, 23 atoms of water will sup- 

 ply the loss in the analysis, for it would amount to 44*947, and 

 the loss is 44*457. It is, however, to be observed, that the esti- 

 mate of 23 atoms of water would agree with the analysis of the 

 salt, upon the supposition that the whole quantity of sulphuric 

 acid belongs to it ; but this is not the case ; for it contains some 

 persulphate of iron which is not combined with ammonia, and 

 which is not united with the same proportion of water as the 

 triple salt. 



On closely examining the crystals, I observed that they efflo- 

 resce slightly, and become brown on the surface. In order to 

 decide the question, I employed Dr. Thomson's method of cal- 

 culating the exact quantity of nitrate of barytes necessary to 

 decompose the whole of the sulphate of ammonia andiron. On 

 the supposition that it contains 24 atoms of water, 11-83 parts 

 of sulphate of iron and ammonia would exactly decompose 13-06 

 of nitrate of barytes, and if only 23 atoms of water, then 11-61. 

 of the triple salt would be required to decompose the same 

 quantity of the nitrate. The crystals employed in this experi- 

 ment were rendered perfectly colourless by repeated crystalliza- 

 tion, and when decomposing such a portion of them by means 

 of that quantity of nitrate of barytes which indicates the presence 

 of 24 atoms of water, I found so little sulphuric acid remaining 

 unacted upon, that when more nitrate of barytes was added no 

 turbidness was occasioned for several minutes. This slight 



