1816.) Scientific Intelligence. 399 
state it here ; because it is easy, and by far the cheapest mode with 
which | am acquainted. Take one part of green sulphate of iron 
and four parts of black oxide of manganese ; reduce both to powder, 
and mix them well together. Then expose the mixture to a red 
heat in acrucible, The dry mass, when digested in water, lets a 
sulphate of manganese dissolve which is entirely free from iron and 
copper. Care must be taken that the oxide of manganese employed 
be free from lime; otherwise the quantity of sulphate of manganese 
obtained will be small in proportion to the quantity of that earth 
present. 
VII, Native Carlonate of Strontian. 
Some time ago. dissolved 3 oz. 400 gr., or 1840 gr., of the 
native carbonate from Strontian, in Argylshire, in nitric acid, and 
separated the nitrate of strontian by crystallization. After having 
separated three or four different crops of crystals, there remained 
behind a mother liquid, from which I could procure no more nitrate 
of strontian, either by spontaneous crystallization or evaporation. 
I therefore evaporated the whole to dryness, and digested the dry 
mass in alcohol. The alcoholic solution being filtered, a white 
powder remained on the filter, which was nitrate of strontian. On 
being dissolved in water, and evaporated, it yielded crystals of pure 
nitrate of strontian to the very last drop. The alcoholic solution 
was evaporated to dryness, and re-dissolved in water. The colour 
of the solution was yellowish brown; but the tinge, I conceive, was 
owing to part of the alcohol having been altered by the beat; for 
ammonia threw down nothing from the liquid, nor altered its 
colour. Carbonate of soda threw down 26 grains of carbonate of 
lime ; but the liquid remained as deeply coloured as ever. 
It appears from this experiment that native carbonate of strontian 
contains a portion of carbonate of lime, either mixed or in combi- 
nation. As 1840 grains yielded 26 grains of carbonate of lime, it 
follows that in the native carbonate of strontian there is contained 
1°41 per cent. of carbonate of lime. During the evaporation of the 
alcoholic solution, a portion of it was accidentally spilled, by a 
sudden motion of the sand-bath on which it was evaporating. 
Hence the quantity of carbonate of lime was greater than I found ; 
perhaps it amounts nearly totwo per cent. Thus it appears that 
native carbonate of strontian contains as much carbonate of lime as 
arragonite does of carbonate of strontian, 
IX. Weight of an Atom of Strontian. 
The weight of an atom of strontian which I gave in my table 
(Annals of Philosophy, vol. ii. p. 46), being founded on experi- 
ments made with native carbonate of strontian, cannot be quite 
correct. I thought it, therefore, proper to make an experiment 
with artificial carbonate, which I knew to be pure. 1 dissolved 600 
ins of nitrate of strontian in water, and precipitated it by car- 
te of soda. The precipitate, after being well washed and dried, 
weighed $00°8 grains of carbonate of strontian. 100 grains of this 
