358 M. Walmstedt's Researches on 



its weight of carbonate of potash. Of the purity of the silica, 

 as it is usually separated, I convinced myself by repeatedly 

 fusing it with potash : I renewed its separation and conversion 

 tofluidity, and treateditwith caustic ammonia, which only occa- 

 sioned a slight flocky precipitate, and this probably resulted only 

 from the corrosion of the filter. And when phosphate of soda 

 was added to it, not the least trace of a precipitate appeared. 



I now boiled the very acid solution, which had been sepa- 

 rated from the silica and was of a greenish yellow colour, for 

 an hour with nitric acid, precipitated it with a little caustic 

 ammonia, boiled the dark-red precipitate half an hour in 

 caastic alkali, and from the alkaline solution mixed with mu- 

 riatic acid I precipitated by carbonate of ammonia some in- 

 considerable flakes of alumina. The remainder which had 

 not been taken up in the caustic alkali was dissolved in mu- 

 riatic acid, and the iron, after a more perfect neutralization, 

 precipitated by means of succinate of soda. When I poured 

 over the precipitate, after it had been well washed, weak so- 

 lution of ammonia, and then evaporated it by a gentle heat, I 

 could not once remark that the platina crucible had been 

 attacked. On re-dissolving the oxide of iron in muriatic acid, 

 there was a residuum for the most part of one and even two 

 milligrammes of gelatinous silica. 



The colourless fluid which had been separated I now 

 mixed with some drops of oxalate of potash and ammonia, 

 but was unable, even after it had been digesting anany days 

 on a warm stove, to discover any trace of a precipitate. Pe- 

 ridot is, however, not free from lime. I next united the solution 

 with the fluid that had been taken from the succinate of iron, 

 precipitated the magnesia with carbonate of potash, accord- 

 ing to the manner laid down by Bonsdorfi^, ascertained the 

 weight of the earth which was ignited, and again dissolved it in 

 muriatic acid, when some fumes of chlorine were disengaged, 

 but this not till towards the conclusion. After the distillation, 

 till I dried it and dissolved it in water acidulated with muriatic 

 acid, silica remained, which never weighed more than 0*6 per 

 cent, and often much less. I now mixed the solution with 

 hydro-sulphuret of ammonia, again dissolve<l the dark-colour- 

 ed precipitate in muriatic acid, and at last precipitated it l)y 

 boiling it with cai-bonate of potash. As the hydro-sulphuret 

 of ammonia contained a solution of magnesia, I mixed it with 

 sulphuric acid till the existing combinations were completely 

 destroyed ; I tlien dried it by evaporation, and heated the 

 residuum till the excess of sulphuric acid had disappeared. 

 As the mass of salt was dissolved by a concentrated sokrtion 

 of gypsum, no doubt remained of the presence of lime, while 



n hUiall, 



