24 An Account of some coloured Svotv and Hoar-frosts 



opaline by the use of tlie ammoniacal oxalate in powder. It 

 was, in short, in appearance similrir to that of snow or common 

 hail. Nevertheless, thrcce kilogrammes of this water, Mhich I 

 reduced bv evajjoration to one decagramme, immediately as- 

 sumed all the qualities of s|)ring water kept long in open vessels. 



The dry sedimcut (the proportional quantity of which with 

 the li([uid I could not precisely ascertain, hut which uiight he 

 about one gramme to three kilogrammes of hail or snow,) was 

 of great tenuity, had an eaithy appearance, was soft to the 

 touch, and was of a dark nankeen yellow colour : it had neither 

 smell nor taste, and v.as completely incomlnistihle when ignited 

 bodies were applied to it. 



It was rough on th.e tongue, shrunk up in the blow-pipe, and 

 became of an ochery red. It gave nothing to boiling water, 

 even after long digestion. I tried the isolated action of the 

 sulphuric, nitric and muriatic acids on this substance. All these 

 acids produced a brisk but short effervescence : they dissolved a 

 part of the substance, and refused to dissolve the rest. 



The solutions are of a fine citron yellow, and the first por- 

 tions of acid employed were the highest coloured. The tone 

 of colour becomes lower v.hen the solution cools. 



All of them give a white precipitate upon the addition of 

 oxalate of ammonia ; and after this re-agent has ceased to jiro- 

 duce the effect, we obtain a precipitate, also white, but more 

 considerable, by means of carbonate of potash. 



The calcareous prussiate forms in it at first a reddish shade, 

 which turns to deep yellow, and afterwards becomes clear : then 

 a small quantity of bhie prussiate is precipitated. The nitric 

 solution is rendered turbid by the nitrate of silver : if we dry it, 

 it presents a v.'hite and not very combustible residue, to which 

 there must be an addition of acid to make it become soluble in 

 water. 



The sulphuric solution wh-n pushed to evaporation over the 

 fire becomes of a deep yellow, and emits sulphifrous acid gas. 

 When the matter is dried, if we pass distilled water into it and 

 filter it, the substance separated from the li(|Uor has the colour 

 of bister, is shining and acid, attracts humidity from the air, and 

 assumes in some measure the aspect of artificial tannin. Its 

 small quantity did not permit me to examine it. The filtered 

 liquid is white and acid : by the addition of a little potash, it 

 crystallizes in tetrahedral pyramids joined by their bases. The 

 carbonisation of the sulphuric -solution is not obtained, if we 

 previously throw on the earthy sediment a little nitric or muria- 

 tic acid. 



In general we may say that the acids succeed but imperfectly 

 in dis&olving it, notwithstanding the action of heat. A consi- 

 derable 



