424. B. G. Bredberg on the green Garnet of Sal a. 



specimen belonged to such as were found at a later period in 

 the same part of the mine, in 1800, by the mining-master 

 M. Billow. There was no apparent ground to expect so great 

 a difference as the analyses afterwards indicated in the com- 

 position of two specimens so similar in their appearance, their 

 conduct beibre the blowpipe, and their form, and which had 

 been found in the same mine. 



Analyses. 



In No. 1, the levigated powder was decomposed by con- 

 centrated muriatic acid, in which it was boiled for three days 

 consecutively, after which the silica remained behind in gela- 

 tinous lumps. In No. 2, on the contrary, the mineral was 

 treated with carbonate of potassa, and exposed to a red-heat in 

 a platinum crucible. In other respects both were proceeded 

 with in the following manner : 



The acid fluid, after the separation of the silica, was precipi- 

 tated by a trifling excess of caustic ammonia ; the precipitate, 

 after the lapse of some hours, was placed on a filter, and 

 washed with boiling water, and then boiled for an hour with 

 caustic potassa. The alkaline solution of alumina was super- 

 saturated with muriatic acid, and the earth precipitated by 

 carbonate of ammonia, washed and exposed to a red-heat. 

 The oxide of iron left undissolved by the caustic lixivium, 

 was dissolved in muriatic acid ; the solution mixed with a little 

 nitrous acid was made boiling hot, then neutralised with caustic 

 ammonia, and precipitated with succinate of ammonia. The 

 succinate of iron was converted to a red oxide in an open 

 platinmn crucible. The fluid obtained after tlie first precipi- 

 tation by caustic ammonia was diluted, warmed, and precipi- 

 tated with a solution of oxalate of potassa; the precipitate col- 

 lected on the filter was washed, and exposed to a red-heat in 

 a platinum crucible. In determining the quantity of lime, I 

 tried it, for the sake of certainty, with carbonate of ammonia, 

 and when, after two or three such trials, no alteration in weight 

 took place, the proportion of lime was calculated from the 

 weight of carbonate of lime thus obtained. The solutions, 

 after the separation of the lime and iron, were put together, 

 mixed with a few drops of muriatic acid, in order to keep the 

 difficultly soluble oxalate of magnesia in a state of solution, 

 and afterwards mixed, in a boiling state, witli a sufficient quan- 

 tity of carbonate of potassa. After evajiorating them to dry- 

 ness, and redissolving in Ijoiling water, they yielded magnesia. 

 In No. 1, a trace of manganese was indicated by this process. 

 In No. 2, on the contrary, the earth was scarcely discoloured 

 after ignition. 



The 



