92 ESSAY V. 



phenomenon, however, it does not follow that it contains no 

 manganese ; the yellowness of the glass is a sign that iron 

 is at the same time present, which is likewise confirmed by 

 the yellow colour of the solution in muriatic acid. Now, 

 since the calx of iron has the same property as gypsum and 

 calx of tin (Sec. XLII. (c)), the red 'colour must also here dis- 

 appear. If only a little nitre be added to the yellow glass, 

 it becomes immediately dark red (Sec. XLII. (d)). Thence it 

 is evident that manganese really enters into the composition 

 of ^potashes. In the ashes of thyme (thymus serpillum), 

 however, I have observed very little ; ashes from wood 

 yield more. 



SECTION XLV.. 



I shall now conclude with an account of some experi- 

 ments which 1 made with a view to discover the constituent 

 parts of manganese. But not having yet been able to 

 produce manganese by art, or to confirm by synthesis what 

 I have learnt by analysis, I am uncertain whether my 

 conclusions, though founded on experiments, are just. I 

 have observed that from phlogisticated manganese, dissolved 

 by vitriolic acid, there separates, after every calcination in 

 the open fire, a quantity of gypsum. The gypsum is indeed 

 in very small quantity ; but I was curious to know whether 

 the manganese loses of its weight in proportion ? This led 

 me to make the following tedious and troublesome experiments 

 with the utmost accuracy : I calcined half an ounce of 

 phlogisticated manganese, purified from all foreign particles, 

 as described (Sec. xix.), upon a finely polished iron plate till 

 it grew quite black. I then dissolved it in diluted vitriolic 

 acid, with the addition of a little sugar, in a sand-heat, till 

 the solution became limpid. After it was cooled, a fine 

 shining powder precipitated, which proved to be selenite ; 



